I gratefully acknowledge the work of the many astronomers, past and present, 
who have contributed positions that I quote for the galaxies, clusters, and 
nebulae.  This is a list of references to their work that I have used.

I must note in particular the list of Galactic globular clusters assembled by 
William Harris (AJ 112, 1487, 1996; 2010 edition is online at 
http://physwww.mcmaster.ca/~harris/mwgc.ref); Bill's Bibliography file 
includes many papers that I had not seen with data for globulars.


N.B.  Quoted and estimated standard deviations are usually internal errors, 
      exclusive of systematic errors.  There are thousands of examples of 
      positions for the same object differing by much more than the quoted 
      errors.

2MSP     2MASS Point Source Catalog (PSC), 2000.  On-line version via VizieR.  
         Note that there are far fewer problems with the point source 
         positions than there are with the extended source positions.  
         Positions going into means calculated for e.g. globular clusters are
         probably for individual red giant stars; enough are usually available
         to insure a reliable mean position.
        *Standard deviation 0.18 arcsec.  
2MSX     2MASS Extended Source Catalog (XSC), 2003.  Some positions from the 
         1st or 2nd Incremental Releases, 1999 and 2000, via NED, but most
         from the on-line version at VizieR.
        *Standard deviation 0.30 arcsec, but much larger accidental errors can
         occur.  I checked all of these before entering them here.  The 
         problems (due to edge-of-scan effects) are largely overcome in the 
         Full-Sky release of 2003, but some remain.
6dF      D. Heath Jones, et al., MNRAS 399, 683, 2009.  The 6dF Galaxy Survey.
         The positions are from the input lists, though with unexplained 
         frequent changes of a few tenths of an arcsecond.  The major lists 
         are 2MSP and 2MSX, which see in this file.  Other positions are from 
         SuperCOSMOS, the Shapley Supercluster Survey, the Horologium sample, 
         ROSAT, HIPASS, IRAS FSC, SUMSS/NVSS radio sample, DENIS, Hamburg-ESO 
         QSO Survey, and the NRAO-VLA Sky Survey.  References for most of 
         these are in Jones et al., MNRAS 355, 747, 2004, with the remainder 
         in this 2009 paper.  The positions are included here as pointers to
         the 6dF redshifts; they are the reference positions for placing the 
         fibers in the spectrograph.
        *Standard deviation typically better than 1.0 arcsec, though depend on 
         the position source.
AA       Arthur Auwers, AN 58, 369, 1862; micrometric observations, usually
         re-reduced.
        *Standard deviation about 2 arcsec at a guess.
AAS      A.A. Schoenmaker, quoted in dBW and vdK2,3 (which see; also see
         van Herk and Schoenmaker, IAU Circular 2334, 1971 and A&A 17, 146,
         1971 for repeat of N5055).  Optical positions for a few bright
         galaxies.
        *Standard deviation about 0.5 arcsec.
AC       R.W. Argyle and E.D. Clements, Observatory 110, 93, 1990.  N = 32
        *Standard deviation about 0.2 arcsec.  
AC22     AC 2000.2.  Stars; and a few planetaries, courtesy Brian Skiff.
         Proper motion almost always ignored.
        *Standard deviation around 0.2-0.3 arcsec at B1950.0.
ACR      R.C. Stone, J.R. Pier, and D.G. Monet, AJ 118, 2488, 1999.
         Astrometric Calibration Regions around the celestial equator.  A few
         galaxies picked up among the 1.2 million stars.  These are tightly
         tied to the ICRS.
        *Standard deviation around 0.03 arcsec (that is not a typo:  0.03"!)
AE       R. W. Argyle and P. Eldridge, MNRAS 243, 504, 1990.  Seyfert
         galaxies.  N = 72
        *Standard deviation about 0.15 arcsec.  
AGK2     A. Kopff and J. Peters.  AGK2.  Astron. Rechen-Inst. Veroff. 16, 
         No. 71.  Positions for objects that can be fairly represented by 
         stars.
        *Standard deviation about 0.3 arcsec (but with systematic errors).
AGK3     AGK3 (check SIMBAD or VizieR for the complete reference).  Positions
         for stellar objects.
        *Standard deviation about 0.3 arcsec (but with systematic errors).
AH       Brent A. Archinal and Steven J. Hynes.  "Star Clusters", 2003, 
         Willmann-Bell, Richmond, VA.  Positions for Galactic, LMC, SMC, M31, 
         and Fornax open and globular clusters.  Positions for Galactic
         globulars are almost always from Source SW (which see), while many 
         open clusters have positions from Source BSV.  The latter are flagged 
         "[From Skiff]"; the systematic RA difference is probably due to
         round-off in a precession routine.  Other position sources are 
         sometimes noted in the comments column.
        *Standard deviation varies, depending on cluster size and position 
         source.
AK       A. N. Argue and C. M. Kenworthy, MNRAS 160, 197, 1972.  NGC 1275.  
         N = 1
        *Standard deviation about 0.2 arcsec.  
AK90     O.B. Aaquist and S. Kwok.  A&AS 84, 229, 1990.  Position for NGC 6807
         pulled in by B.A. Skiff.
        *Standard deviation a few arcsec at a guess.
ALS      Albert Le Sueur, unpublished discoveries with the Great Melbourne
         Telescope, recovered by Steve Gottlieb in 2018 (see sources "Mel" and
         "SGMT" for more information).
        *Standard deviation varies from roughly 8-10 arcsec (for measured
         offsets) to 2+- arcmin (for estimated positions).
AM       H.C. Arp and B.F. Madore.  "Catalogue of Southern Peculiar Galaxies 
         and Associations," Cambridge U. Press, 1987.
        *Standard deviation around 15-20 arcsec.
AMo      R.W. Argyle and L.V. Morrison, IAUC 5976, 1994.  Offsets (9"w, 7"n;
         see Treffers etal. IAUC 5946) from SN 1994D in NGC 4526 for nucleus.
         SN pos is 12 31 29.945 +07 58 36.87 (n=18) +-0.06 arcsec.
        *Standard deviation about an arcsec; depends on offset.
ANS      A.N. Skinner in T.H. Safford, Ann. Rep. Dearborn Obs. 1885-6, p. 37,
         1887 (see source THS below).  Five galaxies (NGC 577, 7416; IC 138,
         210, 1528).
        *Standard deviation 1-2 arcminutes.
APAS     APASS:  The AAVSO Photometric All-Sky Survey.
         See https://www.aavso.org/apass
        *Standard deviation less than an arcsecond for most objects.
APM      S. Maddox et al, MNRAS 243, 692, 1990.  APM Galaxy Catalogue, 1996
         version.  Selected galaxies only.
        *Standard deviation 0.5 arcsec for small galaxies, up to 8-10 arcsec
         for large galaxies.  Use 3 arcsec for the time being.
APMN     Northern APM scans from POSS1 copy plates.  Seems to be free from the
         systematic errors that plague the southern APM positions.
        *Standard deviation for small galaxies 0.2 arcsec, probably around 1-2
         arcsec for large ones.
APMb     J. Loveday et al, MNRAS 278, 1025, 1996.  Selected galaxies from the
         APM Bright Galaxy Catalogue.  Many galaxy images are contaminated by 
         superposed star images, and many others have just plain wrong 
         positions.
        *Standard deviation around 3 arcsec.  I have weeded out those 
         positions with occasional much larger errors.
APMn     A. Naim et al, MNRAS 274, 1107, 1995.  830+- galaxies in the south-
         equatorial zone.  Same problems as the APM Bright Galaxy Catalogue 
         (APMb here, which see), though superposed stars are less frequent.
        *Standard deviation around 8-10 arcsec.
AO       Aoki et al (1991, PASJ 43, 775; pos for IR nucleus of NGC 891)
        *Standard deviation a few arcsec.
AR       R. J. Allen and E. Raimond, A&A 19, 317, 1972.  Maffei 2.  N = 1
        *Standard deviation 2 arcsec.  
ASec     A. Secchi.  AN 66, 11, 1866.  About a dozen objects found by Brother
         Ferraro at College Roman, most now unidentifiable.  Nominal 
         positions.
        *Standard deviation many arcminutes, or more.
Ames     A. Ames, HA 88, No. 1, 1930.  Virgo Cluster survey on four Bruce
         refractor plates.  Only positions that Ames measured herself used 
         here.  She took most NGC/IC positions from the NGC/IC itself. 
        *Standard deviation 20 arcsec at a guess.
AvdM     Anderson, J. and R.P. van der Marel.  ApJ 710, 1032, 2010.  Position
         for Omega Cen (NGC 5139) from HST astrometry and photometry of 
         235,000 stars within 2.5 arcminutes (core radius) of the center.
        *Standard deviation about 1.0 arcsecond.
Bar      E.E. Barnard, various publications.  Micrometric observations, 
         re-reduced w.r.t. modern comparison positions when possible, 
         precessed otherwise.  (See also EEB, below).
        *Standard deviation a few arcsec.
Bax      J. Baxendell.  Nominal position for NGC 7088, a non-existent nebula.
        *Standard deviation meaningless.
Be       L. Becker, Annals of the Edinburgh Observatory No. 1, page 1, 1902.
         Meridian circle observations.
        *Standard deviation around 5 arcsec at a guess.
Beck     S.C. Beck et al.  ApJ 457, 610, 1996.  2-cm and H-alpha peaks for NGC 
         5253; astrometry based on GSC stars.
        *Standard deviation 1-2 arcsec in both coordinates.
Bids     Bidschof, AN 3520.  Micrometric measurements at Vienna Obs.  
         Precessed from 1890.0.
        *Standard deviation around 2 arcsec.
Big      G. Bigourdan, visual micrometric measurements (1884 - 1907) reduced
         by me w.r.t. SAO, AGK3, GSC, or AC positions, taking proper motion
         into account when possible.  
        *Standard deviation varies, usually about 2 arcsec, but is larger for 
         objects with poorly-defined or faint nuclei.
Bige     G. Bigourdan, estimated offset.  
        *Standard deviation anywhere from 3 to 30 arcsec.
Bign     Bigourdan's nominal position for objects not found by me.
        *Standard deviation meaningless unless the objects can be recovered.
Bond     G. P. Bond, AN 1453.  Micrometric observations with the 16-inch 
         Harvard refractor, c. 1850s.  Most are stars.
        *Standard deviation around 20 arcsec at a guess.
Bord     M. Rapaport et al.  A&A 376, 325, 2001.  Bordeaux meridian circle
         positions, extracted by Brian Skiff.
        *Standard deviation around 0.05-0.10 arcsec.
BAA      Brent A. Archinal, private communication (but also see source AH).
         Open clusters.
        *Standard deviation 5-30 arcsec depending on cluster size.
BASm     B. Skiff, means from several different sources, usually for 
         planetaries.
        *Standard deviation around 1-2 arcsec.
BASs     B. Skiff, place holder until I can run down the source that Brian
         used.
        *Standard deviation a few arcsec.
BC       R. Buta and H. Corwin, Ap. J. Suppl. 62, 255, 1986.  Means of several
         sources (calculated by me).  Hercules Cluster.  N = 35
        *Standard deviation better than 1 arcsec.  
BCG      E.J. Barton, R.R. De Carvalho, and M.J. Geller.  AJ 116, 1573, 1998.
         About 500 galaxies in or near compact groups.
        *Standard deviation 2-3 arcsec.
BCGP     Barbieri, C., Capaccioli, M., Ganz, R., and Pinto, G.  AJ 77, 444,
         1972.  Radio sources.
        *Standard deviation about 0.4 arcsec.
BCHR     H. Baumgardt, P. Cote, M. Hilker, M. Rejkuba, S. Mieske, 
         S.G. Djorgovski, and P. Stetson.  MNRAS 396, 2051, 2009.  "Assumed"
         position for NGC 2419; no reference or procedure given.
        *Standard deviation "assumed" to be on the order of 1-2 arcseconds.
BD       Bonner Durchmusterung.  A few BD stars (referred to by e.g. Barnard 
         for IC 4690, and possibly by Tempel for NGC 464).
        *Standard deviation around 0.5 arcmin.
BEE      R.G. Bower, R.S. Ellis, and G. Efstathiou.  MNRAS 234, 725, 1988.
         Galaxies in Abell 2029.
        *Standard deviation around an arcsecond, at a guess.
BGEJ     S.F. Beaulieu, G. Gilmore, R.A.W. Elson, R.A. Johnson, B. Santiago,
         S. Sigurdsson, N. Tanvir.  AJ 121, 2618, 2001.  NGC 6553 from stellar
         distribution near main sequence turnoff; from HST images.
        *Standard deviation 1-2 arcseconds at a guess.
BH       S.W. Burnham and G.W. Hough, AN 106, 64, 1883.  Seven "New Nebulae".
        *Standard deviation around an arcminute at a guess.
BHSB     H. Baumgardt, M. Hilker, A. Sollima, and A. Bellini.  MNRAS 478, 
         1520, 2018.  Positions for Galactic globular clusters, taken from
         GRAD or from W.E. Harris, AJ 112, 1487, 1996.  Convenience!
        *Standard deviation 2-3 arcseconds.
BI       W.A. Baan and J.A. Irwin.  ApJ 446, 602, 1995.  1412.1 and 1655.2 MHz
         observations of the unresolved nuclear source in NGC 3079.
        *Standard deviation around 0.3-0.4 arcsec.
BJM      B.J. McNamara.  PASP, 83, 491, 1971.  Crab pulsar from Lick 36-inch
         plates.
        *Standard deviation around 0.1 arcsec.
BPP      L. Basso, G. Palumbo, R. Primavera, G. Vettolani, and M. Vigotti.
         A&AS 83, 569, 1990.  CGCG galaxies, Paper 4 (see VPS).  Paper copies 
         of microfiche scanned, proofed.
        *Standard deviation depends on size of galaxy, varies from 1 arcsec to 
         5 arcsec.
BSP      Brian Skiff, private communication.  NGC/IC objects, primarily from
         DSS via SkyView.
        *Standard deviation depends on size of object.  For stellar objects, 
         it is around 2 arcsec.  See source BSV.
BSV      Brian Skiff, private communication.  Open clusters and central stars
         of planetaries, measured using SkyView, precessed from J2000.0.
        *Standard deviation depends on size of object.  For planetaries, it is 
         around 2 arcsec; for small compact clusters, around 5 arcsec; for 
         large scattered clusters, around an arcmin.
BSa      B. Santiago, private communication.  SEGC galaxies, measured with
         an overlay.  N = 20
        *Standard deviation about 10 arcsec.
BSc      E. Bica and H. Schmitt, ApJS 110, 41, 1995.  SMC clusters and
         nebulae, from ESO IIIa-F sky survey films.
        *Standard deviation about 10 arcsec.
BTC      Bordeaux Transit Circle.  See 2001A&A...376..325R.  Courtesy Brian
         Skiff; a few planetaries.
        *Standard deviation 0.1 arcsec at a guess (I obviously haven't seen 
         the paper yet.)
CMC      Carlsberg Meridian Transit CCD (CMC-15) drift scans, -40 to +50 
         degrees.  See also D.W. Evans, M.J. Irwin, and L. Helmer; A&A 395, 
         347, 2002.  
        *Standard deviation between 0.035 and 0.10 arcsec for stellar objects,
         probably 0.1 to 0.3 arcsec for galaxies.
Car9     G. Carraro.  AJ 137, 3809, 2009.  Estimated position for AM 4.
        *Standard deviation around 3-5 arcseconds at a guess.
Cer      V. Cerulli, AN 139, 47, 1895; NGC 5898, 5903 micrometrically 
         measured, precessed from equinox 1895.
        *Standard deviation probably 2-3 arcsec
Com      A. Ainslie Common.  Copernicus 1, 50, 1881.  40 nebulae found with a
         36-inch silvered-mirror reflector.  Positions read from setting 
         circles.
        *Standard deviation a few arcminutes.
Cope     Ralph Copeland, found with LdR's 72-inch.  Originally adopted only 
         for missing objects, now used for comparison with modern positions.
        *Standard deviation depends on origin of position; micrometric:  a few
         arcseconds; estimated positions:  a few arcminutes.
CB2,CB2o J.J. Condon and J.J. Broderick.  AJ 102, 1663, 1991.  6-cm and 
         optical positions for galaxies identified with IRAS sources.
        *Standard deviations:  less than 1 arcsec for 6-cm, 0.5 arcsec for
         optical positions given to 0.1 arcsec, 3-5 arcsec for optical given
         to 1 arcsec.
CBF      R. Chandar, L. Bianchi, H.C. Ford.  ApJS 122, 431, 1999.  M33 on HST
         WFPC2 frame.
        *Standard deviation around 0.2-0.3 arcsec.
CCA      W. Cotton, J.J. Condon, E. Arbizzani.  ApJS 125, 409, 1999.
         All UGC galaxies, from DSS.  NGC/IC identifications are mine.
        *Standard deviation:  1.2 arcsec (though CCA added in an additional
         error as a function of diameter as well; I've included their nominal 
         error as a note).
CCBD     J.J. Condon, M.A. Condon, J.J. Broderick, and M.M. Davis.  AJ 88, 20,
         1983.  Optical positions for flat-spectrum radio sources.  Four 
         NGC/IC objects included.
        *Standard deviations:  1 arcsec.
CCR,CCO  J.J. Condon, M.A. Condon, G. Gisler, and J.J. Puschell.  ApJ 252, 
         102, 1982.  6- or 21-cm positions (CCR), or optical positions (CCO) 
         for bright spirals.
        *Standard deviations:  1 arcsec (optical), "smaller than 1 arcsec" 
         (radio).
CDC      P.C. Crane, J.R. Dickel, and J.J. Cowan, ApJ 390, L9, 1992.  3.6 cm
         position for the nucleus of M31.
        *Standard deviation 0.4 arcsec.
CFB,CFBo J.J. Condon, D.T. Frayer, and J.J. Broderick.  AJ 101, 362, 1991.
         6-cm and optical positions for UGC galaxies which are strong radio
         sources.
        *Standard deviations:  less than 1 arcsec for 6-cm, 0.5 arcsec for
         optical positions given to 0.1 arcsec, 3-5 arcsec for optical given
         to 1 arcsec.
CGS      Luis Ho, et al. ApJS 197, A21, 2011.  The Carnegie-Irvine Galaxy
         Survey.  589 bright or large southern galaxies observed with the 
         2.5-m Las Campanas telescope; positions found using Astrometry.net.
         Positions for interacting galaxies are means.  Classifications are 
         from RC3.
        *Standard deviation claimed to be 0.1 arcsecond.  That's for stellar
         objects; for galaxies with nuclei, an informal eyeball comparison 
         suggests 0.3 to 0.5 arcseconds, with an offset to the west of 0.2 to 
         0.4 arcseconds.
CHDM     J.G. Cohen, S. Hsieh, S. Metchev, S.G. Djorgovski, and M. Malkan.
         AJ 133, 99, 2007.  2MASS positions for 11 Galactic globular clusters.
        *Standard deviation around 2-3 arcseconds, except for NGC 6541 -- that
         is place 40 arcsec too far north.
CHFP     C.H.F. Peters, Copernicus 1, 51, 1881.  Positions for a few objects
         determined from his own star charts.  See also "Pe".
        *Standard deviation on the order of 1 arcmin at a guess.
CK       J. Condon and D.L. Kaplan, ApJS 117, 361, 1998.  Optical positions of 
         planetary nebulae measured on DSS.  
        *Standard deviation 1-2 arcsec for stellar planetaries, 5-10 arcsec 
         for larger objects.
CLGE     H.N. Cohn, P. M. Lugger, J.E. Grindlay, and P.D. Edmonds.  ApJ 571, 
         818, 2002.  Terzan 5 from centroiding on HST images.
        *Standard deviation 1 arcsecond.
CP       C. Pollas, Observatoire de la Cote d'Azur, IAU Circulars Nos. 5076,
         5141, 5147, 5421; parent galaxies of SNe.
        *Standard deviation probably 1-2 arcsec
CSD      E. Corbelli, E. E. Salpeter, and J. M. Dickey, ApJ 370, 49, 1991.
         Positions for galaxies in two rich clusters, including Abell 400.
        *Standard deviation a few arcsec.
CSe      C. Seligman, "Celestial Atlas" at 
         http://cseligman.com/text/atlas/ngc00.htm .  A few positions sent to 
         me beginning in 2013, generally corrections to some of my older or
         approximate places (e.g. IC 336).
        *Standard deviation varies, indicated by precision given, one or two 
         in the last place given.
CSP      C. S. Pierce, Harvard Annals, Vol 8, Part 1.  Used only when the
         object is not found (e.g. NGC 1170).
        *Standard deviation 1-2 arcminutes at a guess for verified objects.
CW       Carl Wirtz, Strassburg Annals, 1911.  Precessed from 1900, or
         occasionally re-reduced from the original micrometric offsets.
        *Standard deviation a few arcsec.
d'A      Heinrich d'Arrest, "Siderum Nebulosorum, Observationes Havnienses 
         ...", 1867.  Observed positions precessed from 1861.  Originally 
         included here only for nebulae not found, now often quoted for 
         comparison with modern positions.
        *Standard deviation around 0.5 arcminute.
dA1      Heinrich d'Arrest, "Resultate aus Beobachtungen der Nebelflecken und
         Sternhaufen -- First Series", Abhandlungen der K. Sachsischen 
         Gesellshaft de Wissenschaft, 5, 293, 1856.  Observations with the
         12-cm refractor at Leipzig, 1855-6; and previous observations 
         collected for about 230 objects.  Positions for equinox 1850 quoted
         for comparison with other observers.
        *Standard deviation around 10 arcseconds at a guess.
dBW      A.G. de Bruyn and A.G. Willis.  A&A 33, 351, 1974.  6-cm positions 
         for NGC 2782 and NGC 4151 (RA's only, not included here, for N1068, 
         N3227, and N7469).
        *Standard deviation 1 arcsec or better.
Den      Denning, private communication to Dreyer; taken from NGC.  
         This source will be replaced; positions are place-holders for now.
        *Standard deviation around 2-3 arcmin.
Djo      S. Djorgovski.  ApJ 317, L14, 1987.  Three obscured globular 
         clusters:  Djorg 1, Djorg 2 = ESO 456-SC038, and NGC 6540 = Djorg 3.
        *Standard deviation "about 3[arcsec] in either coordinate."
DAD      D.A. Dale, AJ, in press.  DSS positions for galaxies in clusters.
        *Standard deviation around 1 arcsec.
DC       L. L. Dressel and J. J. Condon, Ap. J. Suppl. 31, 187, 1976.
        *Standard deviation around 4 arcsec.
DDA+     R. J. Diaz, H. Dottori, M. P. Aguero, E. Mediavilla, I. Rodrigues, 
         and D. Mast, ApJ 652, 1122, 2006.  Position(s) for M83.
        *Standard deviation better than an arcsecond.
DDB      D. D. Balam.  IAUC 6427.  Positions for parent galaxies of SNe.
        *Standard deviation better than 0.5 arcsec.
DEN3     DENIS, Release 3, 2005.  Positions for galaxies, via B. Skiff.
        *Standard deviation about 2 arcsec for brighter galaxies.
DFOT     M. Doi, M. Fukugita, S. Okamura, and K. Tarusawa. ApJS 97, 77, 1995.
         Galaxies brighter than B = 16 within 5 degrees of the Coma Cluster.
        *Standard deviation around 1 arcsec.
DJS[o|r] D.J. Saikia et al.  MNRAS 245, 397, 1990.  Optical and radio 
         positions for nuclear hot spots in NGC 1808.
        *Standard deviation 0.5 arcsec.
DKM1     D. K. Milne, A.J. 78, 239, 1973.  Planetaries.  
        *Standard deviation 6-8 arcsec.
DKM2     D. K. Milne, A.J. 81, 753, 1976.  Planetaries.  
        *Standard deviation 6-8 arcsec.
DLW      D. L. Welch, AJ 101, 538, 1991.  SMC clusters.
        *Standard deviation 5 arcsec.
DM       S. Djorgovski and G. Meylan, 1993, in Structure and Dynamics of
         Globular Clusters, ASP Conference Series No. 50, ed. Djorgovski, S.
         and Meylan, G., ASP (San Francisco), p. 325.  Globulars.  
        *Standard deviation a few arcsec.
DMC      W.S. Dias, H. Monteiro, T.C. Caetano, J.R.D. Lepine, M. Assafin, and
         A.F. Oliveira.  A&A 564, A79, 2014.  See also A&A 389, 871, 2002 and
         the online catalogue at http://www.wilton.unifei.edu.br/ocdb/ .
         Open cluster parameters.
        *Standard deviation 1-3 arcminutes at a guess, dependent on the 
         cluster size.
DS       Delisle Stewart, HA 60.  677 nebulae found on 24-inch Bruce reflector 
         plates taken at Arequipa, Peru.  Used only when the nebula is not
         found or otherwise questionable.  Given to 0.1 minute and 1 arcmin in 
         HA 60.
        *Standard deviation 2-3 arcmin at a guess.
DSFA     M. Cragin, J. Lucyk, B. Rappaport.  The Deep Sky Field Guide to 
         Uranometria 2000.0, 1993, Willmann-Bell (Richmond, VA), quoted by
         B.A. Archinal in Star Clusters (see source AH), for NGC 1881.
        *Standard deviation unknown, probably an arcminute or so.
DWFo     M. J. Drinkwater, R. L. Webster, P. J. Francis, J. J. Condon, 
         S. L. Ellison, D. L. Jauncey, J. Lovell, B. A. Peterson, and 
         A. Savage, MNRAS 284, 85, 1997.  Optical positions for Parkes radio
         sources, taken from the COSMOS/UKST Southern Sky Catalogue, corrected
         for systematic plate-to-plate errors; or from APM scans of the POSS1.
        *Standard deviation 0.8 arcsec.
DWFr     M. J. Drinkwater, R. L. Webster, P. J. Francis, J. J. Condon, 
         S. L. Ellison, D. L. Jauncey, J. Lovell, B. A. Peterson, and 
         A. Savage, MNRAS 284, 85, 1997.  Radio positions for Parkes radio
         sources, observed at the VLA or at the ATCA.
        *Standard deviation about 0.3 - 0.5  arcsec.
dEn      W. d'Engelhardt, monograph.  Micrometric positions for a few NGC and
         IC objects, precessed from 1885.0.
        *Standard deviation 3-5 arcsec at a guess.
ECP      Edward C. Pickering, Harvard Circular No. 5 (NGC 5253) and ApJ 12, 
         52, 1900 (IC 4850).
         Miscellaneous positions, usually measured on Harvard plates.
        *Standard deviation a few arcsec at a guess.
EDC      E. D. Clements, MNRAS 197, 829, 1981. Seyfert Galaxies.  N = 14
        *Standard deviation around 0.15 arcsec.  
EEB      E.E. Barnard, NGC or IC positions precessed, or precessed from his
         published papers if clearly not micrometrically measured.  Some are
         precessed from his "A Photographic Atlas of Selected Regions of the 
         Milky Way" (see it http://www.library.gatech.edu/barnard/).  Some of
         these are for objects not found in any of Barnard's papers published 
         prior to 1908, but others appeared as listed below.  Some positions 
         are exact and may have been micrometrically measured, but most are 
         clearly estimates (NGC 2226 is an example).  I've found one (IC 5259) 
         that is 2.5 min off in RA, and another (IC 5366) that may be 2 
         degrees off in Declination.
         Published papers:  
           For NGC objects:
           AN 2490, 2588, 2624, 2687, 2690, 2691, 2756, 2819, and 2995; 
           Observatory 8, 122, 1885 (= No. 96); Sidereal Messenger 1, 135; 1, 
           168; 1, 238, 1882; 2, 226; 2, 259; 2, 287, 1883; 3, 60; 3, 91; 3, 
           96; 3, 184; 3, 189; 3, 254; 3, 314, 1884; and 4, 39, 1885 (in an 
           article by Swift).
        *Standard deviation varies, but take an arcminute.
EHDS     E. Hummel and D.J. Saikia, A&A 249, 43, 1991.  1.49 GHz and 4.86 GHz
         positions for NGC 4388 and NGC 4438. 
        *Standard deviation 0.5 arcsec at a guess.
EHJ      M. Elmouttie, R.F. Haynes, K.L. Jones, M. Ehle, R. Beck, J.I. 
         Harnett, and R. Wielebinski, MNRAS 284, 830, 1997.  3-cm peak for NGC 
         4945.
        *Standard deviation 2-3 arcsec at a guess.
EHo      Eric Holmberg, Double Galaxy Catalogue, 1937.  Delta RA, delta Dec
         from main galaxy to companions, reduced to RA and Dec by me adopting
         a good position for the main galaxy.  
        *Standard deviation about 10 arcsec.
EJS      E. J. Shaya, et al.  A.J. 111, 2212, 1996.  N = 1.  NGC 1316
        *Standard deviation probably 0.5 arcsec or so.
En       R. Engelmann, AN 104, 193, 1883.  Meridian circle observations.
         Precessed from equinox 1870.0.
        *Standard deviation around 3-5 arcsec; there is probably a systematic 
         offset.
EPA      E. P. Austin, Harvard Annals, Vol. 13, Part 1, 1882.  A few nebulae, 
         most near NGC 3309 and 3311, some micrometrically measured, some not.
        *Standard deviation looks to be on the order of 1-2 arcmin, even for
         the micrometric positions.
ESH      Edward S. Holden.  Publ. Washburn Obs. 1, 73, 1882; 2, 101, 1884; and
         Newcomb, S. USNO Astron. Meteor. Obs. for 1875, 15, 285, 1878 (for 
         NGC 7581; though this observation was perhaps made by H. Tuttle).  
         Twenty five new nebulae and clusters found with the 15.5-inch Clark 
         refractor in 1881 and 1882 (and NGC 7581 with the 26-inch Clark 
         refractor at USNO) with notes on known nebulae; three are not in the
         NGC:  two clusters and Barnard 92, an absorption cloud.
        *Standard deviation a few arcmin; positions given to full seconds
         and full arcminutes, or to full minutes and full arcminutes for three
         objects.
ESO      Andris Lauberts, The ESO/Uppsala Survey of the Quick B Atlas of the
         Southern Sky (Garching: ESO), 1982.  This reference is being replaced
         by the more explicit ESOB as I find them.
        *Standard deviation about 5-6 arcsec.
ESOB     Andris Lauberts, The ESO/Uppsala Survey of the Quick B Atlas of the
         Southern Sky (Garching: ESO), 1982.  
        *Standard deviation about 5-6 arcsec.
ESOLV    A. Lauberts and E. Valentijn, Surface Photometry of the ESO/Uppsala
         Galaxies (Garching: ESO), 1989.  Positions revised from ESO, newly
         measured, or offset from ESO-B position.  
        *Standard deviation about 6-8 arcsec.
EWSo     R.D. Ekers, J.V. Wall, P.A. Shaver, W.M. Goss, R.A.E. Fosbury, 
         I.J. Danziger, A.F.M. Moorwood, D.F. Malin, A.S. Monk, and J.A. 
         Ekers.
         MNRAS 236, 737, 1989.  Optical positions for radio galaxies.
        *Standard deviation 1-1.5 arcsec.
EWSr     R.D. Ekers, J.V. Wall, P.A. Shaver, W.M. Goss, R.A.E. Fosbury, 
         I.J. Danziger, A.F.M. Moorwood, D.F. Malin, A.S. Monk, and J.A. 
         Ekers.
         MNRAS 236, 737, 1989.  6.1-cm positions for radio galaxies.
        *Standard deviation 0.3-0.5 arcsec.
FAB      F.A. Bellamy.  MN 64, 662, 1904.  Position for IC 4996, derived from
         an approximate mean for positions of 103 stars in an area about 15 
         arcmin across.
        *Standard deviation 2-3 arcmin.
FAST     R.C. Stone, J.R. Pier, D.G. Monet, AJ 118, 2488, 1999.  FASTT transit 
         circle.  Courtesy of Brian Skiff; a few planetaries, and the 
         occasional galaxy.
        *Standard deviation (internal) claimed to be at least 0.05 arcsec for 
         the faintest stars, probably 2-3 times that for external comparisons.
FBP      C.B. Foltz, B.M. Peterson, and T.A. Boroson.  Astron. J. 85, 1328,
         1980.  Markarian 701-797.  
        *Standard deviation 1-2 arcsec.
FBi      F. Bidschof. (Ann. K. K. Univ.-Sternw. Wein, 14, 1, 1900).
         Micrometric measurements, precessed from 1897.0.
        *Standard deviation 2-3 arcsec at a guess.
FC       H. Ferguson, A.J. 98, 367, 1989, from hand measures of Las Campanas 
         2.5-m plate.  Fornax Cluster.  (This and sources FSn and FSs replace 
         source HF.)
        *Standard deviation 20 arcsec at a guess.
FCJL     H.C. Ford, P.C. Crane, G.H. Jacoby, D.G. Lawrie, and J.M. van der 
         Hulst.  ApJ 293, 132, 1985.  6 and 20-cm observations of NGC 5194.
        *Standard deviation 0.04 arcsec.
FGLM     E.B. Fomalont, W.M. Goss, A.G. Lyme, R.N. Manchester.  MN 210, 113, 
         1984.  Crab pulsar from VLA observations.
        *Standard deviation 0.1 arcsec
FK5      Fifth Fundamental Catalogue.  Positions for a few bright stars.
        *Standard deviation 0.1 arcsec
FKL      K.C. Freeman, B. Karlsson, G. Lynga, J.F. Burrell, H. van Woerden,
         and W.M. Goss.  A&A 55, 445, 1977.  Optical position for the Circinus
         Galaxy.
FMu      Frank Muller, micrometric measurements, re-reduced using modern
         positions for comparison stars.
FMS      D. Froebrich, H. Meusinger, and A. Scholz.  MNRAS 377, L54, 2007.
         IR position for FSR 1735, a recently discovered Galactic globular
         cluster candidate.
        *Standard deviation 5 arcsec at a guess.
FPB      C.B. Foltz, B.M. Peterson, and T.A. Boroson.  AJ 85, 1328, 1980.
FSn      H. Ferguson, A.J. 98, 367, 1989, from unsaturated PDS scans of IIIa-J 
         plate.  Fornax Cluster.
        *Standard deviation 3 arcsec.
FSs      H. Ferguson, A.J. 98, 367, 1989, from saturated PDS scans of IIIa-J 
         plate.  Fornax Cluster.
        *Standard deviation 10 arcsec at a guess.
FT       J.R. Fisher and R.B. Tully. (A&A 44, 151, 1975). DDO galaxies.
        *Standard deviation 10 arcsec.
Fin      W. H. Finlay.  A few nebulae found with the 6- and 7-inch refractors 
         at Cape Town in the 1880's.  Positions reported here only if the 
         objects are not found.
        *Standard deviation a few arcminutes at a guess.
Gai1     Gaia DR1, A&A 595, A4, 2016.  Note that the epoch is 2015.0, not 
         2000.0 -- proper motion is available only for Tycho-observed stars.  
         Positions for fainter objects are precessed to equinox J2000.0.  I am
         replacing these with Gaia DR2 and EDR3 positions whenever possible.
         See https://www.aanda.org/articles/aa/pdf/2016/11/aa28714-16.pdf and
         http://www.cosmos.esa.int/web/gaia/home for more information.
        *Standard deviation for point sources claimed to be better than 13 mas 
         at m_G = 20.5 at epoch J2015.0, dropping to 0.3 mas at m_G = 17.5 and 
         brighter.
Gai2     Gaia DR2, 2018.  A&A, 616 (special issue), March 2018.  J2000.0 
         positions, parallaxes, and proper motions for 1.332 billion sources; 
         another 361 million ("mostly faint") sources have only mean epoch 
         J2015.5 positions.  See 
         <a href ="https://www.cosmos.esa.int/web/gaia/home"><b>the Gaia web 
         site</b></a> and 
         <a href="https://www.aanda.org/articles/aa/pdf/forth/aa32727-18.pdf">
         <b>Lindegren et al., 2018</b></a> for more information.  The data 
         have been completely reprocessed with more observations added.  Many 
         DR1 sources have disappeared (e.g. NGC 0503) -- search the position 
         files for the note "Not in Gaia DR2." for them.  As if to compensate, 
         many new sources appear in DR2 (e.g. NGC 0505).  Note, too, that 
         there is apparently a 30 <i>micro</i>arcsecond offset from the ICRS
         in the DR2 positions.  This is far below the 10 <i>milli</i>arcsecond
         precision I have chosen for display in the position files.
        *Standard deviation 0.55 mas at m_G = 20 at epoch J2015.5, and better 
         at brighter magnitudes.  Proper motion errors are about 1.1 mas/yr in
         both coordinates at m_G = 20, so position errors at J2000.0 are on 
         the order of 17 mas at m_G = 20.  At m_G = 13, the standard deviation
         is around 0.023 mas at J2015.5, proper motion s.d. 0.05 mas/yr, and 
         parallax s.d. 0.03 mas.  All these values are for point sources.  
         Galaxy nuclei probably have larger errors, 10 mas at a guess.
Gae3     Gaia Early Data Release 3 (EDR3), 2020.  Available at CDS (via VizieR 
         for my work) 3 December 2020.  Improved positions, parallaxes, and 
         proper motions based on 34 months of data.  The reference epoch is 
         J2016.0.  Documentation is available at CDS where this is catalogue 
         number I/350.  Also see the documentation at 
         https://gea.esac.esa.int/archive/documentation/GEDR3/index.html for
         details.  Many sources missing from DR2 have been restored in EDR3 --
         I have filled them in.  The "early" data release of DR3 includes the
         final positions, parallaxes, and proper motions.  The "final" data
         release of DR3, scheduled for sometime in 2022, will have some 
         additional data:  radial velocities, spectra, solar system data,
         variability information, multiple star results, and additional 
         astrophysical parameters based on the spectra.
        *Standard deviation claimed as 0.01-0.02 mas at m_G < 15, 0.05 mas at 
         m_G = 17, 0.4 mas at m_G = 20, and 1.0 mas at m_G = 21 for point
         sources.  The documentation cited above has more detail and caveats.
         I caution again that galaxy nuclei probably have larger errors than
         stellar point sources.
GrV      G. Grueff and M. Vigotti.  A&AS 6, 1, 1972.  Positions for B2 radio 
         sources identified with galaxies.
        *Standard deviation 2-3 arcsec.
GC       J.R. Glanfield and M.J. Cameron. Aust. J. Phys. 20, 613, 1967.
         139 Bright galaxies south of +20 degrees.
        *Standard deviation 15 arcsec.
GD       Glen Deen, private communication.  Numbers in comments column are
         major diameters if unlabeled.
        *Standard deviation 5-6 arcsec at a guess.
GDC      [Unknown source].  Position for IC 2373 = UGC 04409.
GGH      N.A. Grogin, M.J. Geller, and J.P. Huchra.  ApJS 119, 277, 1998.
         Galaxies within 15 degrees of 3C 273, most from CGCG.
        *Standard deviation 1-2 arcsec.
GGN      S. Garcia-Burillo, M. Guelin, and N. Neininger, IRAM preprint No. 
         416, 1996 (to appear in A&A).  Kinematic center of NGC 5907 from 
         high-resolution CO(1-0) observations.
        *Standard deviation on the order of 1 arcsec.
GH       Gallouet and Heidmann (A&A Suppl. 3, 325, 1971). RC1 galaxies, -2deg
         to +26deg.  
        *Standard deviation 4-6 arcsec.
GHD1     Gallouet, Heidmann, and Dampierre (A&A Suppl. 12, 89, 1973).  RC1
         galaxies, +26deg to +90deg.
        *Standard deviation 4-6 arcsec.
GHD2     Gallouet, Heidmann, and Dampierre (A&A Suppl. 19, 1, 1975).  RC1
         galaxies, -2deg to -33deg.
        *Standard deviation 4-6 arcsec.
GJM      L.J. Greenhill, D.R. Jiang, J.M. Moran, M.J. Reid, K.-Y. Lo, and
         M.J. Claussen.  ApJ 440, 619, 1995.  Water maser in the nucleus of
         NGC 4258.
        *Standard deviation 0.1 arcsec.
GMH      L.J. Greenhill, J.M. Moran, and J.R. Herrnstein.  ApJ 481, L23, 1997.
         VLBA position for the water maser in the nucleus of NGC 4945.
        *Standard deviation 0.1 arcsec.
GMKM     P. Goudfrooij, J. Mack, M. Kissler-Patig, G. Meylan, and D. Minniti.
         MNRAS, 322, 643, 2001.  Optical position for NGC 1316, "derived from
         archival HST/WFPC2 images".  
        *Standard deviation on the order of 0.3 arcsec at a guess.
GMS      G. M. Searle, micrometric observations in HA 60.  Re-reduced when
         offsets given.
        *Standard deviation about 2 arcsec at a guess.  
GPB      R.E. Goodson, J.J. Palimaka, and A.H. Bridle.  AJ 84, 1111, 1979.
         Radio sources and a few companions.
        *Standard deviation about 0.4 arcsec.
GR       G. Rumker.  AN 1508, 1866.  Ring micrometer measurements with a 
         4-inch, F15 refractor of known nebulae and a "nova" (NGC 1724).
        *Standard deviation a few arcsec.
GRAD     R. Goldsbury, H.B. Richer, J. Anderson, A. Dotter, A. Sarajedini, and
         K. Woodley.  AJ 140, 1830, 2010.  Positions for Galactic globulars 
         from ellipse fitting to inner 2 arcminutes on Hubble ACS images.
        *Standard deviation on the order of an arcsecond, perhaps better.
GRP      L. Gregorini, H.R. de Ruiter, P. Parma, E.M. Sadler, G. Vettolani, 
         and R.D. Ekers.  A&AS 106, 1, 1994.  Optical positions for "dumbbell"
         galaxies in rich southern clusters.
        *Standard deviation about 2 arcsec.
GSC      Guide Star Catalog, V1.1 (Space Telescope Science Institute, 1991).
        *Standard deviation 1-2 arcsec.  The final digits (0.01 sec, 0.1 
         arcsec are barely significant, and are carried for roundoff 
         protection.
GSC2     Guide Star Catalog, V2.2 (Space Telescope Science Institute, 2001).
        *Standard deviation 0.2-0.3 arcsec for stellar images.
GSC3     Guide Star Catalog, V2.3 (Space Telescope Science Institute, 2006).
        *Standard deviation 0.2-0.3 arcsec for stellar images.
GSCm     Mean of "several" objects from Guide Star Catalog, V1.1 (STScI, 
         1991), typically for double or multiple stars.
        *Standard deviation 2-10 arcsec, depending on separation.
GSCA     GSC-ACT.  Re-reduction of GSC 1.1 by Bill Gray using ACT stars as the
         reference frame.  Also called GSC "1.3" by CDS.
        *Standard deviation about 0.3-0.4 arcsec for stellar objects.
GSCM     Dan Moaz, et al.  1996ApJS..107..215M.  "An Atlas of HST UV Images of
         Nearby Galaxies."  From GASP images; intensity weighted centroids, 
         similar to GSC.  N = 110
        *Standard deviation 1-2 arcsec, though occasional accidental errors 
         due to distorted isophotes can be up to 5 arcsec.
GSCT     D.A. Turnshek, et al. A.J. 99, 1243, 1990.  3 globulars, 2 galaxies,
         from the Guide Star Catalog "using the Center of Gravity centroiding
         method, mean error 1 arcsec."  For stellar objects, yes, but not for
         these five "non-stellar" objects.
        *Standard deviation 5-10 arcsec.
GSWr/o   R.D. Gehrz, R.A. Sramek, and D.W. Weedman.  ApJ 267, 551, 1983.
         6 and 20-cm observations of NGC 3690e and w (incorrectly called NGC 
         3690 and IC 694), and H-alpha peaks (read from their maps).
        *Standard deviation better than 0.3 arcsec for the radio observations,
         0.5 for the optical.
GVW      G.V. Williams.  IAUC 6427.  Positions for nuclei of SN parent 
         galaxies.
        *Standard deviation better than 0.5 arcsec.
GWH      G. W. Hough, AN 106, 63, 1883 (AN 2524).  Nebulae found in May 1883 
         while searching for Comet d'Arrest.
        *Standard deviation a few arcminutes.
GYSB     P. Guhathakurta, B. Yanny, D.P. Schneider, and J.N. Bahcall.  AJ 111,
         267, 1996.  M15
        *Standard deviation about 0.3 arcsec.
Ha10     W.E. Harris.  http://physwww.mcmaster.ca/~harris/Databases.html .
         Positions for Galactic globular clusters (BH 176, ESO 452-SC011, and
         Palomar 15) "measured from DSS R image[s]".
        *Standard deviation probably a few arcseconds.
Hart     E. Hartwig, AN 112, 407, 1885.  Five new nebulae found with the 
         18-inch refractor at Strassburg, micrometrically measured.
        *Standard deviation about 5 arcsec.
Harv     Harvard Annals, Vol. 8.  Nominal position for NGC 3097, now lost.
        *Standard deviation an arcminute or so for other objects from this
         source.
Hee      D.S. Heeshan. ApJ 151, L135, 1968.  NGC 1052.
        *Standard deviation around 0.5 arcsec.
Hi06     Hilker, M. A&A 448, 171, 2006.  Positions for Galactic globular 
         clusters (Arp-Madore 1, Palomar 3, and Palomar 14) from VLT Johnson
         BV images of probable member stars.
        *Standard deviation about 2 arcseconds.
Hip      Hipparcos.  See M.A.C. Perryman et al., A&A 323, 49L, 1997 and 
         F. van Leeuwen, A&A 474, 653, 2007.  These stars essentially define 
         the ICRS, the optical portion of the ICRF.
        *Standard deviation 0.01 arcsec or less.
Hu       Edwin Hubble, Publ. Yerkes Obs. 4, Part II, 1917.  Photographic
         positions, refered to AGK1 stars, precessed.
        *Standard deviation about 5 arcsec.
HC       My own measurements with an engineering scale, astrometrically
         reduced, generally on the PSS prints, sometimes from the IIIa-J 
         Southern Sky Survey films.  
        *Standard deviation about 5 arcsec.
HC2m     My own measurements using IPAC Skyview with 2MASS J-band images for 
         galaxy nuclei (intensity-weighted centroids using Skyview's "examine" 
         command).  Most of the nuclei are stellar in the 2MASS frames.
        *Standard deviation 0.15 arcsec internal, in both RA and Dec, from 
         measurements of Tycho-2 stars in the same 2MASS frames.
HC2s     My own measurements using GSFC SkyView with 2MASS J-band images via 
         WWW, picked right off their image display.  See source HCsv for 
         comments on accuracy.  The 2MASS positions from SkyView do not have 
         the 1+- arcsecond offset to the north that the HCsv positions do. 
        *Standard deviation probably around 0.5 arcseconds, but this is an
         estimate.
HCcd     My own measurements using CCDSoft's "Centroidal Coordinates" feature;
         or, if noted "eyeball" in the Notes column, estimated by eye usually
         because the "Centroidal Coordinates" failed.  Both methods are 
         dependent on CCDSoft's interpretation of the DSS astrometry, and are 
         offset from the "true" position by 1.7 arcsec to the south.  I 
         collected these to verify positions for objects with only one 
         measurement, and picked up others in the field of the target object.
        *Standard deviation about 2 arcsec for well-defined stellar images or
         small galaxies, up to an arcminute or more for large clusters.
HCds     My own measurements using IPAC Skyview with DSS images downloaded 
         from GSFC's SkyView or STScI.  Precision for all measurements is 
         0.1 seconds and 1 arcsecond.  (Previous releases gave intensity 
         weighted centroids using Skyview "examine" command to 0.01 seconds 
         and 0.1 arcseconds, even though the extra digits were not 
         significant.  Positions from the "pick" command have always been
         given to 0.1 seconds and 1 arcsec.)  Note that an early version of 
         Skyview had a bug in the "examine" command such that the centroids 
         were calculated incorrectly (R. B. Hartley, private commumication).  
         The introduced error, however, must have still been within the 
         standard deviation quoted below (see Corwin et al, PASP 110, 779, 
         1998; the paper was written before the bug was found).  Nevertheless, 
         informal comparison with positions from e.g. 2MSP, UCAC, and SDSS has 
         shown that the errors in the HCds positions are considerably larger 
         than calculated earlier.
        *Standard deviation (calculated) 0.8 arcsecond for well-defined images 
         (for "examine"-derived positions), 1.0-1.2 arcsec for "pick"-derived
         positions (see the Corwin et al paper cited just above), 2-5 arcsec 
         for large or overexposed images (both methods).  A more realistic
         estimate for the standard deviation would be on the order of 1.5-2
         arcseconds for the "examine"-measured positions.
HCe      My own measurements for very large diffuse nebulae or large open
         clusters.  Positions are the estimated center of gravity of the 
         object's image on the POSS prints or DSS, and are adequate for 
         identification.  
        *Standard deviation about a few arcminutes.
HCht     My own measurements from HST images.  Details are in the Notes for 
         each object.
        *Standard deviation about 0.1 arcsec, dominated by systematic error.
HChw     My own measurements in 1970-71 for NGC/IC objects on the Hodge-Wright
         LMC Atlas charts.
        *Standard deviation about 10 arcsec.
HCm      Means from several sources, determined by me.
        *Standard deviation usually better than 1 arcsecond, but depends on 
         sources used and centering.  If the mean is for two or more objects,
         the standard deviation is of course dependent on the mean seperation.
HCo      My own measurements, offset from GSC stars unless noted, generally on
         the PSS prints, sometimes on the IIIa-J Southern Sky Survey films.  I 
         have replaced all of these positions.
        *Standard deviation around 2 arcsec if the GSC star/galaxy is within
         2 arcmin of the object, around 4-5 arcsec for larger distances.
HCos     My own measurements, offset from SAO stars, generally on the PSS
         prints, sometimes on the IIIa-J SSS films.  All are now replaced or
         rejected.
        *Standard deviation is around 10-15 arcsec; larger accidental errors 
         are not uncommon.
HCp      My own measurements using the Edinburgh XY machine, astrometrically
         reduced w.r.t. SAO stars.  Indus Supercluster galaxies.
        *Standard deviation better than 2 arc second, but subject to 
         systematic errors in the SAO positions.
HCns     My own measurements using IPAC Skyview with NEAT/SkyMorph images
         downloaded from GSFC's SkyView.  See HCds for more info.
        *Standard deviation probably 1-1.5 arcsec.
HCps     My own estimates using Pan-STARRS1 images downloaded from the PS1 
         image server at STScI; nuclei or hotspots centered in a 6-arcsecond
         window.
        *Standard deviation 0.5 arcsec at a guess.
HCrs     My own measurements using RealSky images.  RealSkyView positions are
         given to 0.1 sec and 1 arcsec, Skyview positions to 0.01 sec and 0.1
         arcsec.  Reference system is AGK3.
        *Standard deviation around 1-2 arcsecond for small galaxies, 2-3 
         arcsec for larger or brighter ones using RealSkyView.  Probably a bit 
         better for positions from Skyview (but see HCds above).
HCsc     My own measurements on SuperCOSMOS images.
        *Standard deviation probably 0.3 to 0.4 arcsec, from comparison with
         my 2MASS measurements (source HC2m, which see).
HCsd     My own measurements using GSFC SkyView with downloaded SDSS images,
         or picked off magnified SDSS DS9, 12, or 13 images.  These, of 
         course, rely on the SDSS astrometric calibration; that has proved to
         be excellent in most fields.
        *Standard deviation around 0.3 arcsecond.
HCsv     My own measurements using GSFC SkyView with the DSS via WWW, picked
         right off their image display.  Accuracy is dependent, of course, on 
         their calibration.  If the position is given to a precision of 0.01 
         seconds of time and 0.1 arcseconds, the display has been expanded 
         enough to show individual pixels.  In those cases, the standard 
         deviation in position is on the order of 1 arcsecond (or perhaps 
         less).  For stellar images and galaxy nuclei, there is a systematic 
         offset toward the north of about 0.8 arcseconds and toward the west 
         of about 0.05 seconds of time; the source of this offset is unknown, 
         but it persists across the sky.  Open cluster positions are for the 
         apparent centroid of the stellar distribution; dimensions of those 
         clusters are referred to that position.  Globular cluster positions 
         are estimated for the center of the "core" of the cluster.  Compact 
         clusters almost always have overexposed cores; scattered clusters 
         sometimes have no obvious cores.  In both cases, the estimated 
         positions are considerably more uncertain than suggested here.
        *Standard deviation around 1 arcsecond for precision given to 0.1
         arcsecond, 2-3 arcseconds otherwise.
HCSb     My own measurements on B-band FITS images from the SINGS survey.  See
         R.C. Kennicutt et al. PASP 115, 928, 2003.
        *Standard deviation a few tenths of an arcsec; depends on SINGS
         astrometric calibration.
HCSD     My own measurements on SDSS images from their server, using their
         astrometric calibration, reading the position from their image.  
         These positions are for unusual objects that have few or no automated
         positions measured.  NGC 3664A is an example.
        *Standard deviation probably around an arcsecond.
HCvl     My own estimates on DSS images via VizieR's current version of
         Aladin-Java.
        *Standard deviation looks to be around 1-2 arcsec; dependent, 
         of course, on the astrometric calibration that the VizieR folks used.
         Round-off digits carried along.
HDW      E. Hummel, R.-J. Dettmar, and R. Wielebinski.  A&A 166, 97, 1986.
         NGC 55.  Center of maximum HI symmetry coincides with blue-light peak
         (see G. de Vaucouleurs, ApJ 133, 405, 1961).
        *Standard deviation 5-10 arcsec at a guess.
HEDM     Deidre A. Hunter, Bruce G. Elmegreen, Trent J. Dupuy, and Michael
         Mortonson.  AJ 126, 1836, 2003.  Clusters in the Magellanic Clouds.
        *Standard deviation 3-5 arcsec at a guess.
HH       Herbert Howe, Monthly Notices series from 1898 to 1900:  
         MNRAS 58, 356, 1898; 58, 515, 1898; 58, 523, 1898; 60, 129, 1899;
         60, 130, 1899; 60, 611, 1900; 61, 29, 1900.  A description of his
         micrometer is in MNRAS 60, 140, 1899.
         Visual micrometric positions precessed from equinox 1900.0.  Standard 
         stars and offsets are not given.
        *Standard deviations are around 5-10 arcsec at a guess.
HHD      E. Hummel, J.M. van der Hulst, and J.M. Dickey.  A&AS 134, 207, 1984.
         VLA 2, 6, and 20-cm observations of 16 galaxies.
        *Standard deviation 0.1 arcsec.
HHKK     E. Hummel, J.M. van der Hulst, W.C. Keel, and R.C. Kennicutt, Jr.
         A&AS, 70, 517, 1987.  1.49 GHz VLA observations of 75 galaxies.
        *Standard deviations are better than one arcsec.
HJKC     R.L. Hurt, T.H. Jarrett, J.D. Kirkpatrick, R.M. Cutri, 
         S.E. Schneider, M. Skrutskie, W. van Driel.  AJ 120, 1876, 2000.
         Positions for a galaxy (2MASX J0730080-220105) and two globular 
         clusters (2MASS GC01 and 2MASS GC02) near the Galactic plane.
        *Standard deviations 1-2 arcseconds.
HK       H. Kobold, Strassburg Annals, 1909.  Visual micrometric precessed 
         from equinox 1900, or re-reduced taking proper motion into account
         if possible.  Noted if not re-reduced.
        *Standard deviation 2-3 arcsec.
HKA      P. Hickson, E. Kindl, J.R. Auman, Ap.J.Suppl. 70, 687, 1989.
         Galaxies in compact groups.  
        *Standard deviation 2-3 arcsec.
HR       W. K. Huchtmeier and O.-G. Richter.  A General Catalogue of HI
         Observations of Galaxies.  New York: Springer-Verlag, 1989.  Interim
         source; most positions are not original.
        *Standard deviation around 10 arcsec.
HSA+     C. Hazard, J. Sutton, A.N. Argue, C.M. Kenworthy, L.V. Morrison, and
         C.A. Murray.  Nature (Phys. Sci.) 233, 189, 1971.  3C 273.
        *Standard deviation 0.2 arcsec.
HS1      H. Schultz,  Monograph, AN 1541, AN 1555.   Micrometric positions, 
         re-reduced with modern positions for the reference stars.  All 
         positions here are also in HS2, but the offsets are given here.
        *Standard deviation 2-3 arcsec.
HS2      H. Schultz,  MNRAS 35, 135, 1875.  Micrometric positions, precessed.
        *Standard deviation 2-3 arcsec.
HSOY     M. Altmann, S. Roeser, M. Demleitner, U. Bastian, and E. Schilbach.
         A&A 600, L4, 2017.  PPMXL was compared with Gaia DR1 to derive 
         interim proper motions until Gaia DR2 appeared.  Thus, "HSOY" is an
         acronym for "Hot Stuff for One Year".  As with UCAC5, there seem to
         be fewer galaxies represented in HSOY than in the input catalogues,
         USNO-B1.0 and 2MASS which led to PPMXL, and Gaia DR1.
        *Standard deviation is "well below 0.1 arcsec".
HWD      H.W. Duerbeck, Space Science Reviews 45, 1, 1987.  Catalogue of
         Classical Novae.  
        *Standard deviation unknown, probably depends on original source.  
         Those that I've checked on DSS are within an arcsec.
HZ       A. Hill and D. Zaritsky, AJ 131, 414, 2006.  SMC clusters from
         photometric scans.
        *Standard deviation 10-20 arcseconds, probably goes with cluster
         diameter.  There are occasional blunders, too (e.g. NGC 294).
I1       S. Ishikawa, Ann. Tokyo Astron. Obs., 2nd Ser., 21, 437.  Virgo
         Cluster area dwarves.  
        *Standard deviation appears to be about 2 arcsec.
IC       J. Dreyer, Index Catalogues.  These positions were determined by 
         Dreyer himself from charts or written descriptions of the nebulae in
         their fields (see e.g. IC 360, IC 5132, IC 5133).
        *Standard deviation varies depending on original source, typically a
         few in the last digit given.
ICRF     C. Ma et al., "The Second Realization of the International Celestial 
         Reference Frame by Very Long Baseline Interferometry", IERS Technical
         Note No. 35, 2009; and A.L. Fey et al., AJ 150, 58, 2015.
         These are the 3414 compact radio sources, including 295 "defining"
         sources, in distant galaxies and quasars that define the ICRS.  A few 
         represent the nuclei of NGC galaxies.
        *Standard deviation on the order of 40 microarcseconds.
IDB      R. Garnier, G. Paturel, C. Petit, M.C. Marthinet, and J. Rousseau.
         "An Image Database."  Positions derived from scanned images of POSS1.
        *Standard deviation appears to be around 5-10 arcsec.  Large 
         accidental errors are common, however, and many "galaxies" are 
         actually stars or have stars nearby included in the image.
IPds     Igor Pesenson.  Measurements using IPAC Skyview "pick" command with 
         DSS images clipped from 10X compressed CD-ROMs.
        *Standard deviation 1.2 arcsecond for small, well-defined images, 2-5 
         arcsec for larger galaxies.
IR       Isaac Roberts.  IC objects found on his 20-inch reflector plates.
        *Standard deviation varies depending on size of object.
IRAS     IRAS Point Source or Small-Scale Structure Catalogues. 1987.
         I'm replacing these with optical positions.
        *Standard deviation about 15 arcsec, but varies widely depending on 
         number of scans, position on sky, etc.  
Inn      R.T.A. Innes, MNRAS 58, 329, 1898; MNRAS 59, 339, 1899; and MNRAS 62, 
         468, 1902; observations with a 7-inch refractor at Cape Town.  About 
         a dozen objects; some micrometric measurements, some circle settings.
        *Standard deviation varies, depending on observing method.
J        S. Javelle, from IC.  Re-reduced using modern positions for 
         comparison stars.  
        *Standard deviation around 4-5 arcsec, but there are occasional 
         blunders in these lists.
JA       Jason Adamik, private communication via Glen Deen.
        *Standard deviation 5-6 arcsec at a guess.
JB       J. G. Bolton, PASP 80, 5, 1968.  N = 1 (N1068)
        *Standard deviation around 0.5 arcsec.
JBGS     D.L. Jauncey, M.J. Batty, S. Gulkis, and A. Savage, AJ 87, 763, 1982.
         Optical positions for Parkes radio sources.
        *Standard deviation "estimated" at 1 arcsecond.
JCR,JCO  J.J. Condon. ApJ 242, 894, 1980.  6-cm and optical positions for
         compact radio sources and nuclei of bright spirals.
        *Standard deviations:  1 arcsec (optical), 0.3 arcsec (radio).
JFJS     J.F.J. Schmidt, AN 57, 161, 1862; AN 64, 1, 1865; and AN 70, 343, 
         1868; micrometric observations, precessed.
        *Standard deviation 2-4 arcsec at a guess, but there may be systematic 
         errors, too.
JFJs     J.F.J. Schmidt, AN 64, 1, 1865.  Nominal position for NGC 4471, not
         micrometrically measured.
        *Standard deviation 30 arcsec at a guess.
JFSF     J.F.J. Schmidt, AN 88, 138, 1876 (AN 2097).  Nominal positions for 
         Fornax Cluster objects, apparently not micrometrically measured.
        *Standard deviation 1 arcmin at a guess.
JG       W. Jaffe and G. Gavazzi, AJ 91, 204, 1986.  Coma Supercluster.
        *Standard deviation around 2 arcsec when position is given to 0.01 
         seconds and 0.1 arcsec.  A few positions are apparently accurate to 
         0.1 second and 1 arcsec, and 1 second and 0.1 arcmin; these are 
         obviously less accurate.  Positions apparently accurate to 0.1 minute
         and 1 arcmin are from CGCG, and were not entered into the position 
         files.
JGr      J. Gretchen, priv. comm. via B. A. Skiff.  Nuclei of bright galaxies,
         from multiple short exposure CCD frames with a 15-cm reflector 
         (3 arcsec/pixel), reduced wrt GSC 2.2 stars.
        *Standard deviation 0.2-0.4 arcsec.
JGL      J.G. Lohse, from NGC (not otherwise published).  Originally used when 
         the object is unrecoverable, now includes identified objects for 
         comparison with modern positions.
        *Standard deviation 2-3 arcminutes.
JGV      W. Jaffe, G. Gavazzi, and E. Valentijn, AJ 91, 204, 1986.  Groups in
         the Coma Supercluster.
        *Standard deviation around 2 arcsec.
JH       J.F.W. Herschel.  Phil. Trans. 123, 359, 1833; and "Results ... Cape
         of Good Hope ...", 1847.  Quoted primarily for star clusters and 
         diffuse nebulae.
        *Standard deviation about an arcminute.
JJ       J.E. Jones and B.T. Jones, MNRAS 191, 685, 1980.  Fornax Cluster.
        *Standard deviation around 10 arcsec.
JJJT     G.C. Joshi, Y.C. Joshi, S. Joshi, R.K. Tyagi, New Astron. 40, 68, 
         2015.  Position and parameters for NGC 110.
        *Standard deviation an arcminute at a guess.
JK       James Keeler, Lick Obs. Publ. 8, 1908.  Measured on Lick Obs.
         36-inch reflector plates.  
        *Standard deviation 2-3 arcsec, may have systematic errors depending
         on the (unspecified) reference star system -- but doesn't look like 
         it.
JL       J. Lunt, MNRAS 62, 468, 1902.  Discovery positions for five IC 
         objects, given to 0.1 minutes of time, 1 arcminute; and two others
         given to 0.1 seconds of time, 0.1 arcminute.  Only the position for
         IC 2621 is close; the others are up to 30 arcminutes off.
        *Standard deviation varies, but is large, on the order of several 
         arcminutes.
JMcA     P.A. Jones and W.B. McAdam, ApJS 80, 137, 1992.  Optical positons for 
         southern radio sources.
        *Standard deviation 0.5 arcsec.
JMS      J.M. Schaeberle, PASP 4, 85, 1892.  Position for IC 405, probably for
         1900, from a 6-inch "Willard lens" plate taken at Lick Obs in March
         1892.
        *Standard deviation a few arcminutes.
JPa      J. Palisa, AN 116, 337, 1887; AN 135, 341, 1894; AN 143, 49, 1897.  
         Micrometric positions for a few NGC/IC objects, precessed.
        *Standard deviation 2-3 arcsec at a guess.
JPL      JPL HORIZONS ephemeris system applied to Comet C/1898 M1 Giacobini
         which is probably IC 4977 (which see).
        *Standard deviation a few arcseconds at a guess.
JSMo     D.L. Jauncey, A. Savage, D.D. Morabito, R.A. Preston, G.D. Nicolson,
JSMr     and A.K. Tzioumis.  AJ 98, 54, 1989.  Optical positions for a few
         radio sources with NGC identifications.
        *Standard deviation probably around one arcsec for optical positions,
         and around 0.3 arcsec for radio positions.
JT       Juan Thome, Cordoba Durchmusterung.  Positions for a few IC objects.
        *Standard deviation 30 arcsec at a guess.
Knn      n = 1,17.  Kiso Ultraviolet Galaxy, list nn.  Complete list in 
         B. Takase and N. Miyauchi-Isobe, Publ. Natl. Astron. Obs. Japan, 3, 
         169, 1993.  Positions for pairs not used.  Here are the individual
         references:
         K01      1984AnTok..192.595T
         K02      1985AnTok..202.237T
         K03      1985AnTok..202.335T
         K04      1986AnTok..212.127T
         K05      1986AnTok..212.181T
         K06      1987AnTok..212.251T
         K07      1987AnTok..212.363T
         K08      1988AnTok..222..41T
         K09      1989PNAOJ...1...11T
         K10      1989PNAOJ...1...97T
         K11      1990PNAOJ...1..181T
         K12      1991PNAOJ...2....7T
         K13      1991PNAOJ...2...37T
         K14      1991PNAOJ...2..239T
         K15      1992PNAOJ...2..399T
         K16      1992PNAOJ...2..573T
         K17      1993PNAOJ...3...21T
         K10a     1997PNAOJ...4..153M
        *Standard deviation claimed to be 0.5 arcsec for stars; it is 1 arcsec
         for the smaller galaxies, and will be worse for the larger ones,
         probably on the order of 2 - 3 arcsec.
Ka83     J.D. Kaler.  ApJ 271, 188, 1983.  Positions for planetary nebulae, 
         brought in by B.A. Skiff.
        *Standard deviation a few arcsec at a guess.
Ko+      G. Kojoian and colleagues, VV galaxies, unpublished.
        *Standard deviation varies from 2 arcsec to more than 20 arcsec 
         depending on size of galaxy.
KAR      P.C. van der Kruit, R.J. Allen, A.H. Rots.  A&A 55, 421, 1977.
         Optical position for NGC 6946.
KCA      G. Kojoian, P.A. Chute, C.A. Aumann.  AJ 89, 332, 1984.
         Markarian 1400-1500.  
        *Standard deviation 1-2 arcsec.
KD       King, I.R. et al. 1993, ApJ, in press (reported in DM, which see).
         Globulars.  
        *Standard deviation a few arcsec.
KEBA     G. Kojoian, R. Elliott, M. Bicay, and M. Arakelian, AJ 86, 820, 1981.
         Arakelian galaxies.  N = 203.  
        *Standard deviation "about 1.5 arcsec," but large accidental errors 
         are relatively common (perhaps up to 5% of the list).
KEB1     G. Kojoian, R. Elliott, and M.D. Bicay.  Astron. J. 86, 816, 1981.
         Markarian 1096-1302.  
        *Standard deviation 1-2 arcsec.
KEB2     G. Kojoian, R. Elliott, and M.D. Bicay.  Astron. J. 87, 1364, 1982.
         Markarian 1303-1399.  
        *Standard deviation about 2 arcsec.
KET1     G. Kojoian, R. Elliott, and H.M. Tovmassian.  Astron. J. 83, 1545,
         1978.  Markarian 508-700.  
        *Standard deviation about 5 arcsec.
KET2     G. Kojoian, R. Elliott, and H.M. Tovmassian.  Astron. J. 86, 811,
         1981.  Markarian 798-1095.  
        *Standard deviation 1-2 arcsec.
KGM      P.T. Kondratko, L.J. Greenhill, J.M. Moran, et al.  ApJ 638, 100, 
         2006.  VLA positions of water masers in Seyfert galaxies.
        *Standard deviation 0.3 arcsec.
KGo      P. Kilmartin and A. Gilmore, IAUC 5951, 1994.  Offsets (9"w, 7"n; see
         Treffers etal. IAUC 5946) from SN 1994D in NGC 4526 for nucleus.  SN
         pos is 12 31 29.92 +07 58 36.5 +-0.3 arcsec.
        *Standard deviation about one arcsec; depends mostly on offset.
KHJ      Arnold R. Klemola, Robert B. Hanson, and Burton F. Jones.  AJ, 94, 
         501, 1987.
         Lick Northern Proper Motion Program: NPM1 Reference Galaxies.  N =
         50,517.  Mostly faint (B > 16) galaxies, but many brighter, serving
         as reference sources for the Lick Proper Motion survey.  About 1900
         NGC and IC galaxies included.
        *Standard deviation 0.2 - 0.3 arcsec.
KHo,KHr  W.C. Keel and E. Hummel.  A&A 194, 90, 1988.  Optical and 6-cm 
         positions for NGC 2655.
        *Standard deviation close to 1 arcsec.
KIBO     R. Kurtev, V.D. Ivanov, J. Borissova, and S. Ortolani.  A&A 489,
         583, 2008.  Position for the Galactic globular cluster GLIMPSE C02.
        *Standard deviation a few arcseconds.
KJBR     S. Koposov, J.T.A. de Jong, V. Belokurov, H.-W. Rix, D.B. Zucker,
         N.W. Evans, G. Gilmore, M.J. Irwin, and E.F. Bell.  ApJ 669, 337,
         2007.  Two low-luminosity Galactic globular clusters, Koposov 1 & 2.
        *Standard deviation 
KK       V.E. Karachentseva and I.D. Karachentsev.  A&AS 127, 409, 1998.
         A list of new nearby dwarf galaxy candidates.
        *Standard deviation around 5-10 arcsec at a guess.
KKP      I. Karachentsev, V. Karachentseva, S. Parnovsky.  Flat Galaxy 
         Catalogue, AN 314, 97, 1993 (revised version with better positions
         published in 1999; see NED for the full reference).
        *Standard deviation around 15 arcsec, but frequent larger blunders.
KLSn     n = 1,i. R. Kirshner, B. Leibundgut, and C. Smith, IAU Circular No.
         4900, 4982, 1989-90.  Two (so far) galaxies with supernovae.
        *Standard deviation "better than 2 arcsec."
KMBD     H.A. Kobulnicky, A.J. Monson, B.A. Buckalew, J.M. Darnel, and 25
         more.  AJ 129, 239, 2005.  Position for the Galactic globular cluster
         GLIMPSE C01.
        *Standard deviation on the order of 2-5 arcseconds.
KMGW     F. Kerber, R.P. Mignani, F. Guglielmetti, and A. Wicenec.  A&A 408,
         1029, 2003.  Positions for Galactic planetary nebulae taken from GSC2
         or estimated on DSS2.
        *Standard deviation about 0.4 arcsec for GSC2 positions, 2-5 arcsec
         for estimated positions.
KMH[KA]  M. Kontizas, D.H. Morgan, D. Hatzidimitriou, and E. Kontizas.  A&AS,
         84, 527, 1990.  Clusters in LMC.  "KMHK" is used for positions from
         the original paper.  "KMHA" is used when brought in from Archinal and
         Hynes, Star Clusters (AH, which see).
        *Standard deviation a few arcsec.
KOS      R. Kirshner, A. Oemler, and P. Schechter.  A.J. 83, 1549, 1978.
         Galaxies in 8 high-latitude fields.  
        *Standard deviation about 6-8 arcseconds at a guess.
KP       J. Koornneef and S.R. Pottasch.  A&A 335 277, 1998.  Position for
         the central star of NGC 650/651.
        *Standard deviation 0.005 arcsec internal, about 0.2 external.
KPR      N.V. Kharchenko, A.E. Piskunov, S. Roser, E. Schilbach, and R.-D.
         Scholz.  A&A 440, 403, 2005.  New open clusters found in the "All-Sky
         Compiled Catalogue of 2.5 Million Stars" (ASCC-2.5).
        *Standard deviation probably 2-3 arcmin.
KPS      N.V. Kharchenko, A.E. Piskunov, E. Schilbach, S. Roser, and R.-D.
         Scholz.  A&A 558, A53, 2013.  Catalogue of basic parameters for star
         clusters in the Milky Way.
        *Standard deviation 1-3 arcminutes at a guess, dependent on the size
         of the cluster.
KR       K. Reinmuth, reported by B. Skiff for PNe.
        *Standard deviation around 1 arcsec
KRL      L. Kohoutek, M.L. Roth-Hoeppner, and S. Laustsen.  A&A 162, 232, 
         1986.  Position for the central star of NGC 2818.
        *Standard deviation 0.2 arcsec internal, 1 arcsec external.
KSG      R.A. Knop, B.T. Soifer, J.R. Graham, K. Matthews, D.B. Sanders, and
         N.Z. Scoville.  AJ, 107, 920, 1994.  VV 114 = IC 1623, 3 components,
         optical peaks from CCD maps.
        *Standard deviation around one arcsec.
LaC      N.-L. de la Caille.  Mem. Acad. Roy. Sci., 1755, pp. 286-296 (via K.
         Glyn Jones, "The Search for the Nebulae", 1975, pp. 44-49).
         Southern nebulae and clusters, positions measured with a 0.5-inch 
         refractor.
        *Standard deviation probably 2-3 arcminutes.
Las      W. Lassell.  AN 27, 171, 1848 (= AN 635).  Discovery position for
         NGC 3121.
        *Standard deviation around one arcminute at a guess.
LdR      Lord Rosse (prepared for publication by J.L.E. Dreyer).  
         "Observations ...", Sci. Trans. Dublin Roy. Soc., Vol. II, (Ser. II), 
         1880.
        *Standard deviation varies from a few arcsec for micrometrically-
         measured objects to a few arcmin for those roughly estimated on a
         single night.
LdRo     Lord Rosse (see above) offset, referred to object as noted.  
         [This source removed March 2017; all are now simply "LdR", which 
         see.]
        *Standard deviation depends on accuracy of reference object.  Lord 
         Rosse's and his assistants' measurements are usually good to 3-4 
         arcsec, but larger errors occasionally exist.
Le[n]    F.P. Leavenworth, in AJ 7, 9, 1886 (n = 1) and AJ 7, 57, 1887 (n = 
         2).  Faint nebulae found with the 26-inch refractor at Leander
         McCormick Observatory.  Originally quoted only when the object could 
         not be identified; now often quoted for comparison with modern
         positions.
        *Standard deviation around 1 minute of time in RA (though a large
         number of objects are roughly 2 minutes of time too far east), 2-3 
         arcmin in Dec.
Lo1      W. Lorenz, Strassburg Annals, micrometric observations.
        *Standard deviation 3-4 arcsec at a guess.
Lo2      W. Lorenz, Publ. Astrophys. Obs. Konigstuhl-Heidelberg 6, 19, 1911;
         photographic astrometry for about 180 bright nebulae.
        *Standard deviation 1-2 arcsec at a guess.
LB       R. Love (Nature(PS), 235, 53, 1972) and Bottinelli et al (A&A 12, 
         264, 1971).  N = 1 (Maffei 2).
        *Standard deviation around 10 arcsec.
LBN      B. Lynds.  ApJS 12, 163, 1965.  List of bright nebulae found on 
         POSS1.
        *Standard deviation a few arcminutes.
LCRS     S. Shectman, et al.  ApJ 470, 172, 1996.  Las Campanas Redshift 
         Survey.
        *Standard deviation around 3 arcsec, including systematic errors 
         within individual scans.
LEDA     Accurate positions for MCG galaxies from the Lyon Extragalactic
         Database maintained by G. Paturel, C. Petit, and colleagues.  Many of
         these are from other sources quoted here, but many are new
         measurements on DSS images.  Most of the problems with PGC are
         cleaned up here.
        *Standard deviation is heterogeneous, but is typically a few 
         arcseconds, exclusive of misidentifications.
LGDC     J.-F. Le Campion, M. Geffert, M.R. Dulou, and J. Colin.  A&AS 95, 
         233, 1992.  Accurate position for NGC 7094, brought in by B.A. Skiff.
        *Standard deviation about 0.5 arcsec at a guess.
LHH      P.O. Lindblad, et al. A&AS 120, 403, 1996.  NGC 1365, reduced w.r.t.
         "... a number of Perth standard stars."  The Perth stars are on the
         FK4 system, so the near-exact agreement with Gaia is accidental.
        *Standard deviation a few tenths of an arcsecond at a guess.
LJG      L.J. Greenhill, reported in D.A. Smith and A.S. Wilson.  ApJ, 557, 
         180, 2001.  Radio position for the Circinus galaxy.
        *Standard deviation = 0.1 arcsec.
LK       L. Kohoutek, positions for planetaries, reported by B.A. Skiff.
        *Standard deviation around 1 arcsec
LMc      Micrometric positions from Leander McCormick observers (Ormond Stone, 
         Frank Muller, Francis Leavenworth) in Leander McCormick Publ., Part 
         6, 1893.
        *Standard deviation probably 5-7 arcsec.
LSFV     B. Lanzoni, N. Sanna, F.R. Ferraro, E. Valenti, G. Beccari,
         R.P. Schiavon, R.T. Rood, M. Mapelli, and S. Sigurdsson.  AJ 663,
         1040, 2007.  Center of gravity of NGC 1904.
LT       Lalande, J. de, & Taylor, J. E. 1847. "A catalogue of those stars in 
         the Histoire celeste francaise of Jerome Delalande: for which tables
         of reduction to the epoch 1800 have been published by Professor
         Schumacher ..." accessed March 2017 via Google. (See also J. Lequeux,
         A&A, 567A, 26, 2014.)  Position for NGC 6210 = Lalande 30510.
        *Standard deviation about 4.5 arcsec according to Lequeux.
Mar      A. Marth.  Nebulae found with Laselle's 48-inch reflector at Malta.
         Positions quoted when the nebula is not found, or is questionable.
        *Standard deviation 2-3 arcmin, but larger accidental errors occur.
Mark     E.J. Cooper, "A Catalogue of Stars Near the Ecliptic ...", Vol. 4,
         p. 183, 1856 (the "Markree Catalogue").  The position for NGC 7447 is
         quoted by Auwers in his appendix of new nebulae attached to his 
         reduction of WH's catalogue.
        *Standard deviation probably around 10 arcseconds for identified
         objects.
McB      M. L. McCall and R. J. Buta, AJ 109, 2460, 1995.  Maffei 1 and two
         companions.
        *Standard deviation 0.5 arcsec.
McN      R. H. McNaught, University of Adelaide, Uppsala Schmidt plates or UK
         Schmidt plates for SNe or parent galaxies.  From IAU Circulars Nos. 
         4726, 5071, 5077, 5132, 5334, 5428, 6088.
        *Standard deviation 0.5 arcsec.
Mel      R.L.J. Ellery, (1885) "Observations of the Southern Nebulae made with 
         the Great Melbourne Telescope from 1869 to 1885. Part I. Melbourne."  
         A few objects found or sketched by Pietro Baracchi, Joseph Turner, 
         and/or Albert Le Sueur -- three in the LMC not included in the NGC -- 
         are here.  Many others, also not in the NGC, were never published; 
         see sources "PB", "Tur", and "ALS".
        *Standard deviation probably 1-2 arcmin.
Min      R. Minkowski, AJ 66, 558, 1961.  Positions for 19 galaxies in A2199;
         offsets from NGC 6166 reduced using GSC position.  MCG picked up them
         all from this paper.
        *Standard deviation 5 arcsec.
Mo       C. Monnichmeyer, Publ. Bonn Obs. No. 1, 1895; micrometric
         observations, re-reduced using modern positions.
        *Standard deviation about 2 arcsec.
Mu[n]    Frank Muller, in AJ 7, 9, 1886 (n = 1) and AJ 7, 57, 1887 (n = 2).
         Faint nebulae found with the 26-inch refractor at Leander McCormick 
         Observatory.  Originally quoted only when the object could not be 
         identified; now often quoted for comparison with modern positions.
        *Standard deviation around 1 minute of time in RA (though a large
         number of objects are roughly 2 minutes of time too far east), 2-3 
         arcmin in Dec.
MAMG     D.E. McLaughlin, J. Anderson, G. Meylan, K. Gebhardt, C. Pryor,
         D. Minneti, and S. Phinney.  ApJS 166, 249, 2006.  Position for 
         NGC 104 from HST images.
        *Standard deviation 0.5 arcsec.
MAPS     Minnesota Automated Plate Scanner.  See R.L. Pennington, R.M. 
         Humphreys, S.C. Odewahn, W. Zumach, and P.M. Thurmes, PASP 105, 521, 
         1993 for a description.  
        *Standard deviation about 0.8 arcsec for small images.
MB       M.D. Bicay, thesis, 1988.  (NED refcode is 1988StanU.T00M....B)
        *Standard deviation 10 arcsec.
MCG      Morphological Galaxy Catalogue, B.A. Vorontsov-Velyaminov and 
         colleagues.  Used only for missing objects or (primarily) defects on
         the POSS1 prints.
        *Standard deviation 2-3 arcmin for defects.
MFG      G. Marconi, P. Focardi, L. Greggio, Ap. J. 360, L39, 1990.  One
         incorrect measurement for DDO 210, rejected.
        *Standard deviation meaningless
MFSK     N. Metcalfe, R. Fong, T. Shanks, and D. Kilkenny.  MNRAS 236, 207,
         1989.  Nine UKST fields to B_J ~16.8.  Previously catalogued galaxies
         included.
        *Standard deviation about 2 arcsec.
MG       A.D. Mackey and G.F. Gilmore.  MNRAS 338, 85 and 120, 2003. 
         Positions for "rich" clusters in the Magellanic Clouds.
        *Standard deviation a few arcseconds, though Mackey and Gilmore claim
         repeatability of +- 1 arcsecond with their centering algorithm.
MGGP     R.P. van der Marel, J. Gerssen, P. Guhathakurta, R.C. Peterson, K.
         Gebhardt.  AJ, Dec 2002.  M15.
        *Standard deviation 0.2-0.3 arcsec.
MJC      M.J. Cameron. CSUAC No. 219, October 1970.  121 galaxies with Dec <
         +20 deg and mpg < 12.5.
        *Standard deviation 10 arcsec.
MKA      M. Malkan, D.E. Kleinmann, J. Apt.  ApJ 237, 432, 1980.  UKS 1,
         Liller 1, Terzan 2 (Galactic globulars).  
        *Standard deviation 6-8 arcseconds at a guess.
MLFD     P. Miocchi, et al.  ApJ 774, 151, 2013.  "Centers of gravity" for 26
         Galactic globular clusters from star counts.  12 positions from other 
         sources; see Table 1 in the paper for those sources.  I'll get to
         them.
        *Standard deviations given as 0.1 to >2 arcseconds; look to be on the
         order of 2-3 arcseconds from an informal comparison with other 
         positions collected here.
MMDD     Meylan, G., Mayor, M., Duquennoy, A., and Dubath, P.  A&A 303, 761,
         1995.  NGC 5139; no details given, so I presume this is an estimate.
        *Standard deviation probably on the order of a few arcseconds.
MW       Max Wolf.  Positions from various AN articles for "nebulae", some for
         objects not found on DSS images or POSS1/SERC prints/films, others 
         for large diffuse nebulae.  Most of the missing objects are probably 
         defects on the early Heidelberg plates.
        *Standard deviation a few arcminutes at best for the (usually) very
         large objects.
MW05     Max Wolf, MN 65, 528, 1905.  IC 2118 position, measured by me on  
         Wolf's sketch (Plate 16).
        *Standard deviation probably 2-3 arcmin.
MW08     Max Wolf, AN 4207, 1908.  IC 4895 discovery position.
        *Standard deviation 1 arcmin at a guess.
MW92     Max Wolf, AN 3130, 1892.  Estimated positions for IC 443 and IC 444.
        *Standard deviation 10 arcmin at a guess.
MW1      Max Wolf, Konigstuhl Nebulae, List 1, Publ. Astrophys. Obs. 
         Konigstuhl-Heidelberg, 1, 11, 1902.  154 entries precessed from 1875.
         (N.B.  for List 2, see Schwassmann, source Sn.)  The positions from 
         this series were keyed by Evelyn Deen, and proofread by Glen and 
         Evelyn Deen.  When an object from this series has been verified on a 
         print of the original plate, the comments column has the type from 
         the POSS1 followed by the comment "(verified)".  Not all the plates 
         from this paper have survived, but those that have, have arrowhead 
         marks made by Wolf himself showing his nebulae.
        *Standard deviation 3-5 arcsec.
MW3      Max Wolf, Konigstuhl Nebulae, List 3, Publ. Astrophys. Obs. 
         Konigstuhl-Heidelberg, 1, 125, 1902.  Measured on 16" Bruce refractor 
         plates; precessed from 1875.  Coma Cluster; not included in the IC.
         Dreyer preferred to leave the list "... to the few photographic
         observers likely to study this small part of the heavens ..."
        *Standard deviation 3-5 arcsec.
MW4      Max Wolf, Konigstuhl Nebulae, List 4, Publ. Astrophys. Inst.
         Konigstuhl-Heidelberg, 2, 57, 1906.  272 objects, precessed from 
         1875.  There are no marks on Wolf's plate or the contact print of it 
         that I have, but I have confirmed all objects with DSS2B/R images.
         Those objects not in NGC are in IC2.
        *Standard deviation 3-5 arcsec.
MW5      Max Wolf, Konigstuhl Nebulae, List 5.  Publ. Astrophys. Inst.
         Konigstuhl-Heidelberg, 2, 77, 1906.  239 objects precessed from 1875.
         Most are in IC2, a few are in NGC.  There are many plate defects and 
         faint stars, double stars, etc. in these lists, but the true nebulae 
         have good positions.  Wolf's marks still exist on the original plate, 
         so the contact print I have has enabled me to verify all the objects 
         on POSS1 prints or DSS images.
        *Standard deviation 3-5 arcsec.
MW6      Max Wolf, Konigstuhl Nebulae, List 6.  Publ. Astrophys. Inst.
         Konigstuhl-Heidelberg, 2, 89, 1906.  204 objects precessed from 1875.
         Again, most are in IC2 and have Wolf's marks on the contact print I 
         have of the original plate.  I have verified all objects on POSS1 
         prints or DSS images.
        *Standard deviation 3-5 arcsec.
MW7      Max Wolf, Konigstuhl Nebulae, List 7.  Publ. Astrophys. Inst.
         Konigstuhl-Heidelberg, 3, 77, 1909.  310 objects precessed from 1875.
         Most are IC2 objects, with a few NGC's mixed in.  As with List 4, 
         there are no marks on the contact print I have of the original plate.
         But I have confirmed all objects with DSS2B/R images.
        *Standard deviation 3-5 arcsec.
MW8      Max Wolf, Konigstuhl Nebulae, List 8.  Publ. Astrophys. Inst.
         Konigstuhl-Heidelberg, 3, 87, 1909.  A few NGC and IC objects 
         precessed from 1875.
        *Standard deviation 3-5 arcsec.
MW16     Max Wolf, Konigstuhl Nebulae, List 16.  Veroff. ... Heidelberg, 8, 
         No. 11, p. 18, 1928.  Precessed from 1900.
        *Standard deviation 1-2 arcsec.
MW17     Max Wolf, AN 205, 79, 1917.  Photographic position for NGC 6946,
         precessed from equinox 1917.0.
        *Standard deviation probably around 1 arcsec.
MWP      C. Moss, M. Whittle, and J.E. Pesce.  MNRAS 300, 205, 1998.  Galaxies
         in Abell 1367, measured on POSS prints.  Includes types from a IIIa-J
         Palomar Schmidt plate.
        *Standard deviation less than 2 arcsec.
NG       E. Noyola and K. Gebhardt, AJ 132, 447, 2006.  Galactic globulars.
        *Standard deviation on the order of an arcsecond, perhaps better.
NGB      E. Noyola, K. Gebhardt, and M. Bergmann, ApJ 676, 1008, 2008.  
         NGC 5139.  Refers back to Noyola and Gebhardt 2006.
        *Standard deviation on the order of an arcsecond, perhaps better.
NH       S.G. Neff and J.B. Hutchings.  AJ 103, 1746, 1992.  6- and 20-cm
         positions for IRAS galaxies.
        *Standard deviation 0.5 arcsec.
NGC      J.L.E. Dreyer, NGC.  MemRAS 49, 1, 1888.  Used when there is no other
         source for the position for an object (e.g. NGC 5469), or when the 
         NGC position differs from the expected input position (e.g. NGC 6618
         = M 17).  Some of these come from Dreyer himself working from 
         published or unpublished sources, others from the original observers 
         (e.g. Lohse for NGC 793 and others; Tempel for e.g. NGC 1443, NGC 
         5469 and others).
        *Standard deviation on the order of a few arcmin.
NMP      N.M. Parrish.  Observations of nebulae, re-reduced wrt modern star
         positions, quoted in Ormond Stone, "Southern Nebulae", Publ. Leander
         McCormick Obs, Vol. 1, p. 173, 1893.  RA's determined by clock, Dec's
         by micrometer.
        *Standard deviation, a few arcsec.
OBBa     S. Ortolani, E. Bica, and B. Barbuy.  A&A 361, L57, 2000.  Position
         and parameters for ESO 280-SC006, a Galactic globular cluster.
        *Standard deviation 10 arcsec at a guess.
OBBb     S. Ortolani, E. Bica, and B. Barbuy.  ApJ 646, L115, 2006.  Position
         and parameters for ESO 456-SC078, a Galactic globular cluster.
        *Standard deviation 10 arcsec at a guess.
OCW      O. C. Wendell, Harvard Circular 42, 1899.  Micrometric position for
         IC 4816 = Nova Sgr 1898.  This is the discovery position.
        *Standard deviation probably a few arcsec.
OFKB     J.C. O'Brien, K.C. Freeman, P.C. van der Kruit, and A. Bosma.  A&A 
         515, A60, 2010.  HI position for IC 5052.
        *Standard deviation a few arcsec.
OGLE     G. Pietrzynski, M. Udalski, M. Kubiak, M. Szymanski, P. Wozniak, and 
         K. Zebrun.  Acta Astronomica 48, 175, 1998; and 49, 521, 1999.  
         Clusters in the Magellanic Clouds. 
        *Standard deviation probably a few arcsec.
OSt[n]   Ormond Stone, in AJ 7, 9, 1886 (n = 1) and AJ 7, 57, 1887 (n = 2).  
         Faint nebulae found with the 26-inch refractor at Leander McCormick 
         Observatory.  Originally quoted only when the object could not be 
         identified; now often quoted for comparison with modern positions.
        *Standard deviation around 1 minute of time in RA (though a large
         number of objects are roughly 2 minutes of time too far east), 2-3 
         arcmin in Dec.
OStM     Ormond Stone, in Publ. Leander McCormick Obs. 1, 173, 1893.
         Micrometric positions for about 400 "Southern Nebulae".  There are a 
         few "novae", most of which ended up in IC1.  While many of the 
         objects have good positions here, at least a few (e.g. IC 339, 
         IC 346) have errors of unknown origin, perhaps from misidentified
         comparison stars.
        *Standard deviation a few arcseconds aside from the blunders.
Pds      G. Paturel, C. Petit, Ph. Prugniel, and R. Garnier.  A&AS 140, 89,
         1999.  DSS positions for miscellaneous galaxies.  n = 17335.
         Identifications for many galaxies -- especially the Zwicky compacts 
         -- are suspect and need to be checked.
        *Standard deviation 1-2 arcsecond for well-defined images, 2-5 arcsec
         for larger galaxies.
Pds2     G. Paturel, et al.  A&AS 144, 475, 2000.  See Pds above.
        *Standard deviation 1-2 arcsecond for well-defined images, 2-5 arcsec
         for larger galaxies.
Pe       Peters, C.H.F.  Copernicus 2, 54, 1882; micrometric observations,  
         precessed (see also CHFP).
        *Standard deviation probably around 3-5 arcsec at a guess.
Pec      Pechule, various articles, primarily in AN.  See IC1/2 for a list.
        *Standard deviation 2 arcsec at a guess.
Pick     E.J. Pickering, AN 105, 335, 1883.  Nominal position for NGC 6766;
         claimed to be an emission-line nebula, but there are no planetaries 
         or other obvious nebulae nearby.
        *Standard deviation about an arcminute for identified planetaries in
         this list.
Po       Porter, Cinncinati Obs., micrometric observations re-reduced.
        *Standard deviation around 1-2 arcsec.
Pr       D. Proust, Meudon Observatory, IAU Circular No. 5134.
        *Standard deviation probably 1-2 arcsec.
PA       C. Pollas and D. Albanese, IAU Circular No. 5040.  NGC 5917.
        *Standard deviation probably 1-2 arcsec.
PB       Pietro Baracchi, unpublished discoveries with the Great Melbourne
         Telescope, recovered by Steve Gottlieb in 2018 (see sources "Mel" and
         "SGMT" for more information).
        *Standard deviation varies from roughly 8-10 arcsec (for measured
         offsets) to 2+- arcmin (for estimated positions).
PC       L. Padrielli and R.G. Conway.  A&AS 27, 171, 1977.  4C sources 
         identified with galaxies.
        *Standard deviation 0.8 arcsec.
PCR      P. Parma, R.A. Cameron, and H.R. de Ruiter.  AJ 102, 1960, 1991.
         Optical positions for "dumbbell" galaxies which are radio sources.
        *Standard deviation 2-3 arcsec.
PEES     B.A. Peterson et al.  MNRAS 221, 233, 1986.  Optical positions from
         Southern Sky Survey IIIa-J plates.
        *Standard deviation "better than 1 arcsec."
PES      B.E.J. Pagel, M.G. Edmunds, G. Smith.  MNRAS 193, 219, 1980.  Optical
         position for NGC 1313 and several HII regions in it.
        *Standard deviation a few arcseconds.
PKe      P. Kempf. (Publ. Astrophys. Obs. Potsdam, No. 29, 1892).  Micrometric
         measures, precessed, not re-reduced unless noted.
        *Standard deviation 2-3 arcsec at a guess.
PK67     L. Perek and L. Kohoutek.  Catalogue of Galactic Planetary Nebulae,
         1967.  Positions brought in by B.A. Skiff.
        *Standard deviation a few arcsec at a guess.
PJ       A. Picard and H.M. Johnston.  A&AS 112, 89, 1995.  Positions for 19
         Galactic globular clusters, referred to Hipparcos stars.
        *Standard deviation 2-3 arcseconds.
PL       M. Postman and T. Lauer.  ApJ 440, 28, 1995.  Positions from DSS for
         brightest galaxies in Abell clusters.  Precessed from J2000.0.
        *Standard deviation 1.0 arcsec.
PPAO     S. Piatek, C. Pryor, T.E. Armandroff, and E.W. Olszewski.  AJ 123, 
         2511, 2002.  Draco Dwarf.  Center of isopleths from star counts.
        *Standard deviation "about 0.1 arcminutes".
PPM      Positions and Proper Motions (S. Roeser and U. Bastian, Heidelberg,
         1991). M31, M32, M92, N2261, N6543.  And a few others.
        *Standard deviation about 0.2 arcsec.
PMXL     S. Roeser, M. Demleitner, and E. Schilbach.  PPMXL (AJ 139, 2440, 
         2010).  USNO-B1.0 and 2MASS PSC combined on the ICRS.
        *Standard deviation 0.1 to 0.3 arcsec.
PS1      The Pan-STARRS1 Surveys, Chambers, K.C., et al. 2016, 
         arXiv:1612.05560.  Positions north of -30 degrees, pulled in from
         either the Pan-STARRS website (http://archive.stsci.edu/panstarrs
         /search.php) or from VizieR (catalogue number II/349) for selected
         NGC objects, but all IC objects north of -30.  The positions adopted 
         by VizieR are apparently those "calibrated to Gaia" (see source 
         "Gai1" above) -- few that I've seen so far have differences from Gaia 
         of more than two or three digits in the last place I've listed (0.001 
         seconds of time and 0.01 arcseconds).
        *Standard deviation around 4 milliarcsec for stars.
PWB      N. Paust, D. Wilson, G. van Belle.  AJ 148, 19, 2014.  Positions for
         the old open clusters Koposov 1 and 2.
        *Standard deviation on the order of 2-3 arcseconds.
QFW      H. Quintana, P. Fouque, and M.J. Way.  A&A 283, 722, 1994.  Optical
         positions for the NGC 1400/1407 Group, measured on ESO Quick B survey
         copy plate.
        *Standard deviation 1.5 arcsec.
R        Rumker, AN 63, 305, 1864, etc.  Micrometric observations, re-reduced
         with modern positions for the reference stars.
        *Standard deviation probably 2-3 arcsec.
Rup      M.P. Rupen, AJ 102, 48, 1991.  Neutral hydrogen mapping of NGC 891
         and NGC 4565.
        *Standard deviation around 1-2 arcsec.
R16      Karl Reinmuth, Konigstuhl plates, 1916.  Precessed from equinox 1900.
        *Standard deviation probably 2-3 arcsec.
R20      Karl Reinmuth, Konigstuhl plates, 1920.  Precessed from equinox 1900.
        *Standard deviation probably 2-3 arcsec.
R27      Karl Reinmuth 1927 list of Virgo Cluster galaxies.  
        *Standard deviation about 2-3 arcsec, but there may be systematic 
         errors depending on reference star system.
R28      Karl Reinmuth, Veroff. ... Heidelberg 8, 133, 1928.  Precessed from
         equinox 1900.0.
        *Standard deviation around 2-3 arcsec at a guess.  See previous.
R29      Karl Reinmuth, Veroff. ... Heidelberg 8, 167, 1929.  Precessed from
         equinox 1900.0.
        *Standard deviation around 1 arcsec at a guess.  See previous.
R32      Karl Reinmuth, Veroff. ... Heidelberg 8, 192, 1932.  Precessed from
         equinox 1900.0.
        *Standard deviation around 1 arcsec at a guess.  See previous.
RB       R. J. Buta, ApJS XX, XXX, 1987.  Position for lsb galaxy "160 arcsec
         west, 34 arcsec south of NGC 7531."
        *Standard deviation probably 0.1-0.2 arcminutes at a guess.
RC       Ralph Copeland, quoted in NGC for NGC 295, not found.
        *Standard deviation meaningless.
RC2      Second Reference Catalogue of Bright Galaxies (de Vaucouleurs et al.
         1976), primarily from GH, GHD1,2 (see above), Cameron, Glanfield and
         Cameron (bright southern galaxies, all replaced by ESO), Sandage's 
         southern lists, and my own measurements (source HC, above).  These 
         are being replaced as I identify the original sources.
        *Standard deviation runs from 5 arcsec to 20 arcsec.
RC3      Third Reference Catalogue of Bright Galaxies (de Vaucouleurs et al. 
         1991).  Not used as a source of positions.
        *Standard deviation varies between 1 arcsec and 20 arcsec.
RD       D. Reynaud and D. Downes, A&A 319, 737, 1997.
         Dynamical center of NGC 1530 from high-resolution CO(1-0) 
         observations.
        *Standard deviation on the order of 1 arcsec.
REds     R. Erdmann, priv. comm.  DSS for NGC 971 and star near NGC 3807.
        *Standard deviation on the order of 1 arcsec.
RF       Royal H. Frost, HA 60, 177, 1908.  453 nebulae found on 24-inch Bruce 
         reflector plates taken at Arequipa, Peru.  Most often quoted only 
         when the nebula is not found or otherwise questionable.  Given to 0.1 
         minute and 1 arcminute in HA 60.
        *Standard deviation 2-3 arcmin at a guess.
RG       R.F. Griffin, AJ 68, 421, 1963.  Galaxies in the fields of 3C 
         sources.
        *Standard deviation 0.3 arcsec.
RGMH     R. Giovanelli, M. Haynes, and colleagues; various papers.  
        *Standard deviation about 6 arcsec.
RGO      Royal Greenwich Observatory, (Dreyer?), MNRAS 71, 509, 1911.
         Photographic positions for far northern galaxies poorly observed by 
         the Herschels, precessed from equinox 1900.0.
        *Standard deviation about 1 arcsec at a guess, though there could be 
         systematic offsets depending on reference system.  
RH       O.-G. Richter, W.K. Huchtmeier, and colleagues.  Optical positions 
         for galaxies in their HI Catalogue and/or various papers.
        *Standard deviation 8-10 arcsec.
RL       G.H. Rieke and F.J. Low.  ApJ 176, L95, 1972.  10-um position for
         nucleus of NGC 253.
        *Standard deviation around 1 arcsec.
RLT      G.H. Rieke, M.J. Lebofksy, R.I. Thompson, F.J. Low, and A.T. 
         Tokunaga.  ApJ 238, 24, 1980.  2.2-um position for M82, "about 3 
         arcsec off the visual peak."
        *Standard deviation 1.5 arcsec.
RSA      Allan Sandage and Gustav A. Tammann.  The Revised Shapley-Ames
         Catalogue ..., Carnegie Publication #635, second edition, 1987.
        *Standard deviation around 10 arcsec.
RTBB     H.J.A. Rottgering, Y. Tang, M.A.R. Bremer, A.G. de Bruyn, G.K. Miley,
         R.B. Rengelink, M.N. Bremer.  MNRAS 282, 1033, 1996.  325 MHz 
         position for Markarian 1498 = WN 1626+5153.
        *Standard deviation 4 arcsec.
RWH      R.W. Hunstead.  MNRAS 152, 277, 1971.  Optical positions for radio 
         point sources.  Four bright galaxies (plus fainter not entered).
        *Standard deviation 0.4 arcsec.
RZ       Marc Rafelski and Dennis Zaritsky.  AJ 129, 2701, 2005.  Clusters in
         the SMC.
        *Standard deviation 8-10 arcsec with occasional blunders.
SeWe     Setteducati, A.F. and Weaver, H.F.  "Newly Found Star Clusters",
         published by the Radio Astronomy Laboratory at the University of
         California, Berkeley, 1962.  The "Berkeley" list of 104 star clusters
         (mostly open clusters) found on the POSS1 prints.
        *Standard deviation stated to by 5 arcminutes.
Sf       Schoenfeld, micrometric observations, inferred from other lists until
         I can find a copy of his papers.
        *Standard deviation looks to be around 3 arcsec.
Sn       Schwassmann, A.  Publ. Astrophys. Obs. Konigstuhl-Heidelberg 1, 17,
         1902.  Precessed from equinox 1900.0.  301 objects in the Virgo 
         Cluster area, found and measured on a 6-inch plate.  Those not in the
         NGC are in IC2.
        *Standard deviation about 3-5 arcsec.
Spt      R. Spitaler, various publications referenced in NGC and IC.  
         Micrometric positions re-reduced wrt GSC/SAO/PPM/Tycho-2 etc.
        *Standard deviation a few arcsec.
Stn      E. Stephan's original lists, n = 1 - 13.  Micrometric positions,
         re-reduced wrt GSC/SAO/PPM/Tycho-2 etc, or precessed.
         St1 = AN 76, 159, 1870 = AN 1810; and MNRAS 32, 23, 1871
         St2 = AN 78, 295, 1872 = AN 1867; and MNRAS 32, 23, 1871
         St3 = AN 79, 61, 1872 = AN 1876; and MNRAS 32, 231, 1872
         St4 = AN 81, 303, 1873 = AN 1939; and MNRAS 33, 433, 1873
         St5 = AN 83, 51, 1874 = AN 1972; and MNRAS 34, 75, 1873
         St6 = AN 83, 137, 1874 = AN 1977
         St7 = CR 83, 328, 1876
         St8 = MNRAS 37, 334, 1877; and AN 89, 213 and 263, 1877 = AN 2126 and
               AN 2129
         St9 = CR 87, 869, 1878
         St10 = CR 90, 837, 1880
         St11 = CR 92, 1128, 1881; ibid p. 1183; ibid p. 1260; and AN 100,
                209, 1881 = AN 2390.
         St12 = CR 94, 546; 1882; ibid p. 609; and AN 105, 81, 1883 = AN 2502.
         St13 = CR 100, 1043, 1885; ibid p. 1107; and AN 111, 321, 1885 =
                AN 2661.
        *Standard deviation about 3-4 arcsec at a guess, when re-reduced.
StE      E. Stephan, from E. Esmiol's 1916 monograph, re-reduced using modern 
         comparison star positions and proper motions. 
        *Standard deviation about 2-3 arcsec at a guess.
Str      Otto Struve, Melanges math. et astron. ... St. Petersburg, 3, 689 and
         4, 392.
         Positions for galaxies found while searching for comets.
        *Standard deviation a few arcminutes at a guess.
Sxy      Carl Seyfert's dx, dy measurements refered to mean position of NGC
         6027 for other members in the group (PASP 63, 72, 1951).  N = 5
        *Standard deviation a few arcsec.
SwB      Lewis Swift in correspondence to E.E. Barnard, 1881-4 and 1887, noted
         by Gary Kronk (private communication, 2016).  Position for NGC 7455.
Sw[n]    Lewis Swift's original lists, n = 1 - 12, 69, X'.  Originally quoted 
         only when the object in question was not found by me, now often 
         quoted for comparison with modern positions.  Positions from Swift's 
         later lists from Lowe Observatory in Southern California are less 
         accurate than those in the earlier lists from Warner Observatory in 
         Rochester, NY, even though the telescope and mounting were the same.
         Warner Observatory lists:
           NGC:
         Sw1 = AN 112, 313, 1885 = AN 2683 (100 objects)
         Sw2 = AN 113, 306, 1886 = AN 2707 (100 objects)
         Sw3 = AN 115, 153, 1886 = AN 2746 (100 objects)
         Sw4 = AN 115, 257, 1886 = AN 2752 (100 objects)
         Sw5 = AN 116, 33, 1886 = AN 2763 (100 objects)
         Sw6 = AN 117, 217, 1887 = AN 2798 (100 objects)
           IC1:
         Sw7 = AN 120, 33, 1888 = AN 2859 (100 objects)
         Sw8 = AN 122, 241, 1889 = AN 2918 (100 objects)
         Sw9 = AN 126, 49, 1890 = AN 3004 (100 objects)
         Sw10 = AN 129, 361, 1892 = AN 3094 (100 objects)
         Sw69 = AN 126, 49, 1890 = AN 3004 (60 objects, including 25 NGC 
                objects not published in lists 1-6)
         SwX' = MNRAS 53, 273, 1893 (7 objects)
         Lowe Observatory lists:
           IC2:
         Sw11 = AN 147, 209, 1898 = AN 3517 (243 objects)
           Most nebulae in this list were previously published in shorter 
             lists as follows:
           List 1 = PASP 8, 304, 1896 and AJ 17, 27, 1897 (50 objects)
           List 2 = PASP 9, 186 and MNRAS 57, 629, 1897 (25 objects)
           List 3 = PASP 9, 223; MNRAS 57, 631; and PA 5, 426, 1897 (30 objs)
           List 4 = PASP 9, 224; MNRAS 58, 18; and PA 5, 427, 1897 (25 objects)
           List 5 = AJ 18, 111 and AN 145, 283, 1898 (25 objects)
           List 6 = AJ 18, 135; MNRAS 58, 331; and PA 6, 18, 1898 (25 objects)
           List 7 = MNRAS 58, 332; and PA 6, 19, 1898 (25 objects)
           List 8 = MNRAS 58, 333, 1898 (25 objects)
         Sw12 = MNRAS 59, 568, 1899 (45 objects)
        *Standard deviation 3-4 arcminutes, though large accidental errors are
         common, especially in the Sw11 and Sw12 lists.
SAO      SAO position adopted.  Used for a few non-stellar objects, primarily
         planetaries or stars in clusters or in the center of diffuse nebulae.  
         Also used for a few stars thought by the original observer to be
         nebulous -- nebulae may or may not be present on modern photographs.
        *Standard deviation 0.3 to 1.0 arcsec.
SBC      J.L. Sersic, E. Bajaja, and R. Colomb.  A&A 59, 19, 1977.  N2915.
        *Standard deviation a few arcsec (N.B. Sec of RA is wrong in SBC's 
         Table 2.)
SBG1     N. Santagata, L. Basso, M. Gottardi, G. Palumbo, and G. Vettolani.
         A&AS 70, 189, 1987.  CGCG galaxies, Paper 2 (see VPS).  From machine
         readable files sent by G. Palumbo.
        *Standard deviation depends on size of galaxy, varies from 1 arcsec to 
         5 arcsec.
SBG2     N. Santagata, L. Basso, M. Gottardi, G. Palumbo, G. Vettolani, and
         M. Vigotti.  A&AS 70, 191, 1987.  CGCG galaxies, Paper 3 (see VPS).
         From machine readable files sent by G. Palumbo.
        *Standard deviation depends on size of galaxy, varies from 1 arcsec to 
         5 arcsec.
SBIB     D. Sprayberry, G.M. Bernstein, C.D. Impey, G.D. Bothun.  ApJ, 438, 
         72, 1995.  Low surface brightness galaxies.
        *Standard deviation 2-3 arcsec.
SC       Sidney Coolidge.  AN 1453, and the Harvard Zone observations reported
         in various Harvard Annals.  Positions for "nebulae", apparently
         micrometrically measured; or for nebulae not found by me.
        *Standard deviation looks to be around 5 arcsec (or meaningless if not
         found).
SCO      S.C. Odewahn, PhD thesis, Univ of Texas, 1989.  Position for NGC 2366
         from isophotes.
        *Standard deviation a few arcsec at a guess.
SCOS     N.C. Hambly, A.C. Davenhall, M.J. Irwin, H.T. MacGillivray.  MNRAS 
         326, 1315, 2001 and references therein.  Positions from SuperCOSMOS
         scans of sky survey plates.  Tycho-2 provided reference stars.
        *Standard deviation 0.2 arcsec for B_J brighter than 19, 0.3 arcsec 
         for B_J brighter than 22 -- for stellar images, of course.
SDP      S.D. Peterson.  Astron. J. 78, 811, 1973.  Markarian 1 - 507. 
        *Standard deviation 6-8 arcsec.
SDSS     Sloan Digital Sky Survey, 2001-2006+-, sometimes via NED, usually 
         from the on-line version at VizieR.  Tied to Tycho-2 reference stars 
         unless UCAC was available when a given field was done.
        *Standard deviation 0.2 arcsec.
SESO     A. Acker, F. Ochsenbein, B. Stenholm, R. Tylenda, J. Marcout, and
         C. Schohn.  The Strasbourg-ESO Catalogue of Galactic Planetary
         Nebulae (Garching: ESO), 1992.  A few positions quoted by Condon and
         Kaplan, ApJS 117, 361, 1998 (source CK, which see), and by Brian 
         Skiff.
        *Standard deviation unknown, but probably a few arcsec.
SGC      Southern Galaxy Catalogue (Corwin et al. 1985), not from ESOB:  
         visual micrometric measurements (primarily Porter 1911), or my own 
         measurements on PSS or SSS plates/prints/films.
        *Standard deviation 6-8 arcsec or better.
SGMT     Steve Gottlieb, email of 25 August 2018.  Discovery observations of 
         southern nebulae with the Great Melbourne Telescope, gleaned from 
         manuscripts of the Melbourne publication on nebulae (see source "Mel" 
         above and https://collections.museumvictoria.com.au/search?query=
         "Great+Melbourne+Telescope"), and related papers.  Positions are from 
         offsets to previously known objects from JH and WH.
        *Standard deviation perhaps 1-2 arcminutes.
SGsv     Steve Gottlieb, private communication.  Positions for a few objects 
         estimated from SkyView images.
        *Standard deviation 3-4 arcsec at a guess for galaxies, 0.5-1.0 arcmin
         for clusters.
SHM      Kathleen Spellman, George Helou, and Barry Madore (PASP 101, 360,
         1989).  SGC galaxies without ESO positions.  Positions from IRAS;  
         N = 372
        *Standard deviation 8-10 arcsec.  
SIB      Solon I. Bailey, HA 60, 1908.  List of the 263 largest, brightest 
         nebulae and clusters.  Several IC objects here.  Positions given to 
         1 arcmin only; sufficient for identification.
        *Standard deviation 2-3 arcmin.
SIMA     SIMBAD's adopted position for star clusters in the LMC, quoted by
         B.A. Archinal in Star Clusters (see source AH).
        *Standard deviation 10 arcsec at a guess.
SIMB     SIMBAD's adopted position for planetary nebulae (Acker et al, 1996
         version of the Strasbourg Catalogue, CDS catalogue number V/100),
         quoted by B.A. Skiff.
        *Standard deviation around one arcsec.
SJL      A. Sandqvist, S. Jorsater, and P. Lindblad.  A&A 110, 336, 1982.
         Position for NGC 1365 quoted in S. Jorsater and G.A. van Moorsel, AJ
         110, 2037.
        *Standard deviation quoted as 4 arcsec.
SK       E.P. Smith and N.E. Kassim.  AJ 105, 46, 1993.  A few optical 
         positions for 20-cm radio sources.
        *Standard deviation probably around 1-2 arcsec.
SL       Brian A. Skiff, measured on plates taken by Lampland at Lowell Obs.
         PPM stars used for astrometric net.
        *Standard deviation around 0.2-0.3 arcsec.
SMB      E. Slezak, G. Mars, A. Bijaoui, C. Balkowski, P. Fontanelli.  A&AS 
         74, 83, 1988.  Galaxies in the "Coma Supercluster", a Palomar Schmidt
         field north-following A1656, but not including it.  Precessed from
         equinox 2000.0.
        *Standard deviation around 8-10 arcsec.  Large accidental errors have 
         been seen.
SMS1     Wolf, C. et al. PASA 35, 10, 2018.  SkyMapper Southern Sky Survey, 
         DR1.1 via VizieR.  Also see http://skymapper.anu.edu.au/ .  
        *Standard deviation stated as "better than 0.2 arcseconds" based on a
         comparison with Gaia DR1.  For galaxies, it looks more like 0.5
         arcseconds, and seems to vary a bit; perhaps depends on the number of
         scans of an area.  I expect DR2 ... to be better.
SNp      G. J. Garradd, Loomberah, N.S.W.  IAUC No. 6497 for NGC 673, host 
         galaxy for SN 1996bo.
        *Standard deviation ~1 arcsecond at a guess.
SP       E.P. Smith et al.  ApJS 104, 287, 1996.  UV positions from UIT on
         Astro-1 Space Shuttle mission.
        *Standard deviation 2 arcsec.
SPC      Brian A. Skiff, Lowell Observatory PDS scans of 13" Pluto Camera
         (astrographic refractor) plates, 1988 - 89.  SEGC galaxies.  Also 
         miscellaneous positions measured on the same series of plates.
        *Standard deviation 2-3 arcsec.  
SPF      Brian Skiff, but on 18-inch Palomar Schmidt films taken by Gene and
         Caroline Shoemaker for their asteroid search.  
        *Standard deviation is about 1 arcsec.
SPL      S.P. Langley in Harvard Annals 8, Part 1, p. 62, 1882.  Nominal 
         position for NGC 3355; nothing is there.
        *Standard deviation meaningless, but other objects have s.d.'s on the
         order of 10 arcseconds.
SPP      Brian Skiff, on PSS prints or plates.  
        *Standard deviation is around 1 arcsec.
SPZS     P.B. Stetson, E. Pancino, A. Zocchi, N. Sanna, and M. Monelli.  
         MNRAS 485, 3042, 2019.  Positions for 48 Galactic globular clusters.
        *Standard deviation is 5-7 arcsec.
STMW     S.E. Schneider, T.X. Thuan, C. Magri, and J.E. Wadiak.  Ap. J. Suppl.
         72, 245, 1990.  UGC lsb galaxies.  
        *Standard deviation about 10 arcsec.
STMM     S.E. Schneider, T.X. Thuan, C. Magri, and J. Miller.  Ap. J. Suppl.
         81, 5, 1992.  UGC lsb galaxies.  Many positions were apparently taken
         from DC, FT, RGMH, and STMW without acknowledgment; I've removed 
         these.
        *Standard deviation about 10 arcsec.
SW       Stephen Shawl and Raymond White, A.J. 91, 312, 1986.  Positions of
         109 galactic globular clusters. 
        *Standard deviation about 2-3 arcseconds.
SWX      D.A. Smith and A.S. Wilson.  ApJ, 557, 180, 2001.  X-ray position for 
         the Circinus galaxy from a Chandra ACIS map.
        *Standard deviation = 0.1 arcsec.
SVD      Schuyler Van Dyk, private communication.  NGC 150.
        *Standard deviation about 1 arcsec.
T[n]     W. Tempel. n = list number (see NGC introduction).  Positions 
         precessed from Tempel's equinox, typically around 1880, or taken from 
         his descriptions.
        *Standard deviation probably a few arcsec for micrometric measures, 
         1-2 arcmin (at a guess) for others.
TBM      C. Tappert, D. Barria, I. Fuentes Morales, N. Vogt, A. Ederoclite, 
         and L. Schmidtobreick.  MNRAS, in press, 2016 = astro-ph preprint
         number 1608.00527v1.  Position (w.r.t. UCAC4 stars), photometry, and 
         spectroscopy for IC 4850 = V606 Aql = Nova 1899.
        *Standard deviation 0.3 arcseconds. 
TDM      Tom DeMary, open cluster positions from USNO A2.0 displayed with 
         HyperSky, eyeball centers, precessed from J2000.0.
        *Standard deviations between about 10 arcsec to 1-2 arcmin, depending 
         on cluster size.
TE       Thomas Espin, MNRAS 54, 327, 1894; and AN 152, 141 (No. 3633), 1900.  
         Fifteen "nebulae" or clusters in MN (IC1), six in AN (IC2).
         Positions estimated from BD charts.
        *Standard deviation probably 2-3 arcminutes.
TH       Turner, J.L. and Ho, P.T.P. ApJ, 421, 122, 1994.  2- and 6-cm nuclear
         continuum sources in 8 spiral galaxies.
        *Standard deviation 0.5 arcsec, except for NGC 5194 where it is 0.1 
         arcsec.
TH1      Turner, J.L. and Ho, P.T.P. ApJ, 268, L79, 1983.  2- and 6-cm nuclear
         sources in 3 spiral galaxies.
        *Standard deviation about an arcsec.
THB      Turner, J.L, Ho, P.T.P., and Beck, S.C. AJ 116, 1212, 1998.  2- and 
         6-cm continuum observations of NGC 5253.
        *Standard deviation a few tenths of an arcsec.
THC      W. G. Tifft, Hilsman, K. A., and L. C. Corrado.  ApJ 199, 16, 1975.
         18 galaxies in the NGC 507 group, measured on a 90-inch Steward 
         plate.
        *Standard deviation a few tenths of an arcsec.
THS      T. H. Safford, from the NGC Appendix and the IC, and the "Annual 
         Report of the Board of Directors of the Chicago Astronomical Society,
         together with the Report of the Director of the Dearborn Observatory
         for 1885 and 1886", p. 37, 1887.
        *Standard deviation typically a few arcminutes after gross errors are
         removed.
THSH     T. H. Safford, AN 1453.  Positions of stars in the Harvard Zones near 
         three "clusters":  NGC 2189 (two clusters), and NGC 2198.  The 
         clusters themselves are probably unrecoverable.  (N.B.  Safford's 
         initials are incorrectly given in the AN paper and in the NGC as 
         "J.H."; this is the same T.H. Safford whose list of new nebulae found 
         at Dearborn Observatory form most of the Appendix to the NGC.)
        *Standard deviation a few arcseconds.
TML      J.H. Taylor, R.N. Manchester, A.G. Lyme.  ApJS 88, 529, 1993.  Pulsar
         catalogue.  J2000.0 positions precessed to B1950.0 for a few pulsars
         associated with SNRs (e.g. Crab pulsar = NGC 1952).
        *Standard deviation 0.5 arcsec or better.
TN       W. Tempel.  Positions not published in Tempel's papers (see T[n]
         above), but sent to Dreyer and published in the NGC.  These positions
         do not seem to be as accurate as those published directly by Tempel.
        *Standard deviation perhaps 3-4 arcminutes.
TPS      Thorstensen, J.R., Peters, C.S., and Skinner, J.N.  PASP 122, 1285,
         2010.  J2000.0 position for IC 4816 = Nova Sgr 1898.
        *Standard deviation claimed to be ~0.1 arcsec.
TRC      E. Hog et al.  A&A 335, 65L, 1998.  Tycho Reference Catalogue, 
         primarily for individual stars via SIMBAD.
        *Standard deviation 0.040 arcsec.
TVP      Tully, R.B., Verheijen, M.A.W., Pierce, M.J., Huang, J.-S., and
         Wainscoat, R.J.  AJ 112, 2471, 1996.  Ursa Major Cloud members, from 
         GSC stars on CCD images.
        *Standard deviation about 1 arcsec.
Ter      A. Terzan.  A&A 12, 477, 1971 (also see A&A 15, 336, 1971 for
         renumbering of Terzan 11 and 12).  Galactic globular clusters
        *Standard deviation varies: 3-10 arcseconds for Terzan 1 through 
         Terzan 8, several arcminutes for Terzan 9 - 12.
Tur      Joseph Turner, unpublished discoveries with the Great Melbourne
         Telescope, recovered by Steve Gottlieb in 2018 (see sources "Mel" and
         "SGMT" for more information).
        *Standard deviation varies from roughly 8-10 arcsec (for measured
         offsets) to 2+- arcmin (for estimated positions).
Ty2      E. Hog et al.  A&A 355, 27L, 2000.  Tycho-2 positions, primarily for
         individual stars, but also some planetaries (courtesy of Brian Skiff).
        *Standard deviation 0.007 arcsec for stars brighter than V = 9, 0.06  
         for fainter stars.
UA10     USNO-A1.0.  From scans of original sky survey plates by USNO team 
         headed by D. Monet.  These were entered by Steve Gottlieb for almost 
         all of the IC nebulae and stars found by Max Wolf in his 7th list 
         (see source MW7).  Comments attached to these are Steve's.
        *Standard deviation about 0.3 arcsec for stars, 1-2 arcsec for 
         extended objects (e.g. galaxies) larger than about an arcmin.
UA20     USNO-A2.0.  From scans of original sky survey plates by USNO team 
         headed by D. Monet; reprocessing of A1.0 to put it on ICRS.
        *Standard deviation about 0.2 arcsec for stars, 1-2 arcsec for 
         extended objects (e.g. galaxies) larger than about an arcmin, 
         probably around 0.4 - 0.5 arcsec for smaller galaxies.
UB10     USNO-B1.0.  From scans of original sky survey plates by a USNO team 
         headed by D. Monet.  Pretty much like USNO-A1.0, but includes proper
         motions and star/non-star classifications.
        *Standard deviation about 0.2 arcsec for stars, 1-2 arcsec for 
         extended objects (e.g. galaxies) larger than about an arcmin, 
         probably around 0.3 - 0.5 arcsec for smaller galaxies.
UCAC     USNO CCD Astrograph Catalog ("final" edition) "UCAC4".  N. Zacharias, 
         et al, August 2012.  This fourth edition of UCAC includes bug fixes; 
         improved proper motions from Lick NPM data; APASS optical photometry; 
         and bright stars from FK6, Hipparcos, and Tycho-2.  It replaces
         UCAC1-3, all of which I have replaced in the position files.
        *Standard deviation is around 15 to 20 mas in the magnitude range R = 
         10-14, rising to around 100 mas at the limit of the catalogue around
         R = 16.5.
UCA1     See UCAC, which replaced this.
UCA2     See UCAC, which replaced this.
UCA3     See UCAC, which replaced this.
UCA5     USNO CCD Astrograph Catalog "UCAC5".  N. Zacharias, C. Finch, and J.
         Frouard, AJ 153, 166, 2017.  A complete re-reduction of the UCAC 
         scans using Tycho/Gaia Astrometric Solution (TGAS) stars in the 8-11
         magnitude range as a reference star catalogue.  Proper motions and
         errors are claimed to be much improved over UCAC4, though fewer
         galaxies seem to be represented in UCAC5.
        *Standard deviation is not given for UCAC5 positions; they may be 
         better than UCAC4, but this remains to be tested.
UGCo     UGC Notes offset (from UGC galaxies with a precise positions) in
         arcmin and position angle converted to delta RA and delta Dec.
        *Standard deviation about 6-8 arcsec (also depends on accuracy of 
         position used as reference).
UJ10     UJ 1.0 (sampler of USNO-A1.0, which see).  From scans of short-
         exposure IIIa-J POSS-2 plates by USNO, courtesy of D. Monet.
        *Standard deviation about 0.3 arcsec for stars, 1-2 arcsec for 
         extended objects (galaxies).
URA1     USNO Robotic Astrometric Telescope Catalog "URAT1".  N. Zacharias,
         et al, April 2015.  Update of UCAC with larger, more sensitive CCD.
         ICRS positions for 228 million objects from R = 3 to 18.5, north pole
         to -15 degrees.  Uses 2MASS PSC positions to determine proper motion, 
         so the J2000 positions presented by VizieR are identical to the PSC 
         positions.  Used only when the object is not included in PSC.
        *Standard deviation:  stated 5 to 30-40 mas, probably somewhat more
         for galaxy nuclei. 
USNO     See K.J. Johnston, et al, AJ 110, 880, 1995 for background.  These
         have been replaced when possible by the ICRF positions from Fey et al 
         (AJ 127, 3587, 2004); see ICRF above. 
        *Standard deviation better than 3 milliarcseconds in all cases, and 
         better than 1 milliarcsec in most cases.  Accuracy on this level is
         destroyed by the precession program.  Can ANY precession routine do
         justice to these positions?
UW       J.S. Ulvestad and A.S. Wilson.  ApJ 343, 659, 1989.  2, 6, and 20 cm
         VLA observations of Seyfert nuclei.  n = 27.
        *Standard deviation around 0.2 arcsec.
UWS      J.S. Ulvestad, A.S. Wilson, and R.A. Sramek. AJ 247, 419, 1981. 1.465
         GHz and/or 4.885 GHz VLA observations of Seyfert nuclei.  n = 16.
        *Standard deviation 0.1-0.3 arcsec.
UZC      The Updated Zwicky Catalogue.  E. Falco, et al.  PASP, 111, 438, 
         1999.  GSC or DSS positions for about 19,000 CGCG galaxies with m_p 
         <= 15.5, plus a few hundred other galaxies.  The original list had 
         many misidentifications and stars included; my notes refer to this 
         first list.  These errors have been mostly removed in the published 
         version currently available.
        *Standard deviation around 1-1.5 arcsec.
vdH+     J.M. van der Hulst, P.C. Crane, and W.C. Keel.  AJ 86, 1175, 1981.
         6 cm VLA observations of spiral galaxy nuclei.
        *Standard deviation 0.3 or 0.8 arcsec.
vdK1     P.C. van der Kruit. A&A 15, 110, 1971.  21.2-cm positions for 13
         galaxies.
        *Standard deviation about 2 arcsec.
vdK2,3   P.C. van der Kruit.  A&A 29, 231 and 249, 1973.  21.2-cm positions 
         for bright galaxies.  N3556 position interpolated from contours in 
         Fig. 6 of vdK3 by me.
        *Standard deviation less than 1 arcsec (except for N3556; that is 
         probably 3-4 arcsec).
vLL      van Leeuwen, F., Le Poole, R.S., Reijns, R.A., Freeman, K.C., and
         de Zeeuw, P.T.  A&A 360, 472, 2000.
         NGC 5139.
        *Standard deviation not given, but perhaps on the order of one 
         arcsecond.
Vig      Vigotti, M., Grueff, G., Perley, R., Clark, B.G., Bridle, A.H.
         AJ 98, 419, 1989.  Radio sources measured on POSS prints w.r.t. AGK3
         stars.
        *Standard deviations about 0.7 arcsec for stellar images, probably 
         several arcsec for things like M51.
V        Veron, P. ApJ 144, 861, 1966.  Radio sources.
        *Standard deviation about 1 arcsec.
VC       de Vaucouleurs and Corwin, ApJ 295, 287, 1985.  M31 from several
         astrometric sources.  
        *Standard deviation about 0.2 arcsec.
VCC      B. Bingelli, A. Sandage, and G. A. Tammann.  A.J. 90, 1681, 1985.
         Virgo Cluster Catalog.  
        *Standard deviation about 10 arcsec.
VHSW     S.D. Van Dyk, S.D. Hyman, R.A. Sramek, and K.W. Weiler.  IAU Circular
         6045.  VLA 6- and 20-cm position for NGC 6946.
        *Standard deviation probably 0.2-0.3 arcsec.
VL       G. de Vaucouleurs and R. Leach.  PASP 93, 190, 1981.  M31 and M33.
        *Standard deviation about 0.2 arcsec.
VPC      C.K. Young and M.J. Currie.  A&AS 127, 367, 1998.  The Virgo 
         Photometry Catalogue.  Positions taken from RC3 removed.
        *Standard deviation 3-4 arcsec.
VPD      M.B. Vila, A. Pedlar, R.D. Davies, E. Hummel, and D.J. Axon.  MNRAS
         242, 379, 1990.  20- and 6-cm positions for bright Sbc galaxies.
        *Standard deviation 0.3 arcsec when given to 0.1 arcsec, 2-3 arcsec
         when given to 1 arcsec.
VPS      G. Vettolani, G. Palumbo, and N. Santagata.  A&AS 64, 247, 1986. 
         CGCG galaxies, Paper 1.  From machine readable files sent by G. 
         Palumbo.
        *Standard deviation depends on size of galaxy, varies from 1 arcsec to
         5 arcsec.
VPSc     Ditto, for CGCG fields 502-5.  Typed by me.
        *Standard deviation depends on size of galaxy, varies from 1 arcsec to
         5 arcsec.
VV1,2    Veron, M.P. and Veron, P.  A&A 42, 1, 1975 and A&AS 29, 149, 1977.
         Radio sources.
        *Standard deviation about 0.5 arcsec.
VVAG     Veron, M.P., Veron, P., Adgie, R.L., and Gent, H. A&A 59, L19, 1976.
         Radio sources.
        *Standard deviation about 0.5 arcsec.
Wein     R. Weinberger.  PASP 107, 58, 1995.  Six assorted objects including
         a Galactic globular cluster ("Pyxis").
        *Standard deviation about 10 arcsec.
Win      A. Winnecke, Strassburg Annals, Vol. 3, 1909.  Micrometric
         measurements of several hundred NGC objects, re-reduced using modern
         positions for the reference stars.
        *Standard deviation 1-2 arcsec at a guess.
WinA     A. Winnecke, reported by A. Auwers, Astron. Beob. Konigsberg 34, 155, 
         1862.
        *Standard deviation 2-3 arcmin at a guess.
Wolf     Max Wolf, AN 4082 = AN 171, 27, 1906.  Nominal position for IC 1831,
         currently a lost object.
        *Standard deviation meaningless.
WDP      W.D. Pence, thesis (1981).  NGC 253.
        *Standard deviation a few arcsec.
WF       Williamina P. Fleming, Harvard Annals 60 and references therein.  
         Many are "stars" with emission lines; most of these are PNe, or -- in 
         the LMC -- HII regions.  Other papers (e.g. HA 18, 113, 1890) have
         positions for diffuse nebulae found on Harvard plates.  Positions 
         originally used only when the object cannot be positively identified 
         (e.g. IC 1292), but I've been adding them in as I run across them.  
         Original positions were given to 0.1 minute and 1 arcmin.  (Also see 
         source WPF.)
        *Standard deviation for the identified nebulae have positions 
         typically good to 3-4 arcmin.
WGT      W.G. Tifft; probably Coma Cluster or double galaxies (I've lost the
         reference; check AJ's or ApJ's.  My apologies.).
        *Standard deviation a few arcsec at a guess.
WH       W. Herschel, Collected Papers (ed. Dreyer, 1912).  Offsets reduced
         w.r.t. modern positions for reference stars.  Originally used only 
         for objects not recovered on the sky surveys (e.g. NGC 421, NGC 
         4317), I have now extended it to many other of WH's objects for 
         meaningful comparisons with modern data.
        *Standard deviation is 2-3 arcminutes.
WHI      A.B. Whiting, G.K.T. Hau, M. Irwin.  ApJS 141, 123, 2002.  Dwarf
         galaxy candidates found on Southern Sky Survey plates.
        *Standard deviation 0.1 arcminutes.
WK       W. Keel, reported in CCR (which see).  NGC 992.
        *Standard deviation better than 1 arcsec.
WKDP     M.Y. Wang, S. Koposov, A. Drlica-Wagner, A. Pieres, et al.  ApJ 875,
         L13, 2019.  Position and data for the globular cluster Fornax 6.
        *Standard deviation 2-3 arcseconds at a guess.
WKF      P.A. Woudt, R.C. Kraan-Korteweg, A.P. Fairall, H. Bohringer, 
         V. Cayatte, and I.S. Glass.  A&A 338, 8, 1998.  Two galaxies in
         Abell 3627.
        *Standard deviation 2-3 arcseconds at a guess.
WM       A. S. Wilson and E. J. A. Meurs (A&ASuppl. 33, 407, 1978) Seyferts.
         N = 7.  
        *Standard deviation around 0.2 arcsec.
WMe      Wilson and Meurs, as above, but image noted as "large or asymmetric,
         so the errors are typically a few arcsec."
        *Standard deviation around 3 arcsec at a guess.
Wou      Patrick Woudt, private communication to Brian Skiff, Dec 2009.  
         Recovery position for IC 4544 = IL Nor (see P. Woudt and B. Warner, 
         MNRAS, in press, 2010, for a finding chart).
        *Standard deviation:  Formal accidental error about 0.08 arcsec; based 
         on six 2MASS positions for nearby stars, so a systematic error of 
         about 0.15 arcsec should probably be included.
WPF      Williamina P. Fleming, Harvard Circulars No. 32 and 60.  Various NGC 
         and IC objects found on Harvard plates (see also source WF) with
         positions given to 0.1 seconds of time and 1 arcsecond.
        *Standard deviation 10-15 arcsec.
WR       W. Romanishin.  AJ, Aug 1990.  LSB galaxies.  
        *Standard deviation around 3 arcsec.
WS       Wolfgang Steinicke, 1997.  Positions for NGC/IC objects from RealSky.
         Identifications corrected when known wrong, flagged with a question
         mark when WS position is different from another position and an
         investigation is not yet done.  Declinations are systematically south
         by 2 arcsec.  Many of the flagged positions have been replaced with
         positions from Wolfgang's 2014 and 2015 versions; I will do the rest
         as I run across them.
        *Standard deviation 3 arcsec or better.
WU1      A.S. Wilson and J.S. Ulvestad, ApJ 260, 56, 1982. 6 and 20 cm
         position for NGC 5548.
        *Standard deviation 0.2 arcsec.
WU2      A.S. Wilson and J.S. Ulvestad, ApJ 275, 8, 1983. 6 and 20 cm position 
         for NGC 1068.
        *Standard deviation 0.2 arcsec.
WW       A.S. Wilson and A.G. Willis, ApJ 240, 429, 1980.  6-cm positions for
         Seyfert nuclei.
        *Standard deviation 0.4 arcsec.
WWB      C.G. Wynn-Williams and E.E. Becklin.  ApJ 290, 108, 1985.  Optical 
         (Johnson V) position for NGC 2903 quoted in VPD.
        *Standard deviation better than 1 arcsec.
WWD      D. & B. Wills and J. Douglas.  AJ 78, 521, 1973.  Optical positions
         for radio sources.
        *Standard deviation about 0.5 arcsec.
WYC      A.S. Wilson, Y. Yang, and G. Cecil.  ApJ 560, 689, 2001.  20-cm 
         nuclear source in NGC 4258.
        *Standard deviation 0.1 arcsec.
WZ       Felicia Werchan and Dennis Zaritsky.  AJ 142, 48, 2011.  
         LMC clusters.
        *Standard deviation 10-15 arcsec; occasional blunders, too.
XMM      The XMM-Newton Serendipitous Source Catalogue from the XMM-Newton 
         Survey Science Centre Consortium.  http://xmmssc-www.star.le.ac.uk 
         has details.
        *Standard deviation on the order of 1 arcsec for point sources.
YOF      N. Yasuda, S. Okamura, and M. Fukugita.  ApJS 96, 359, 1995.
         Optical positions for spirals in Virgo.
        *Standard deviation 0.9 arcsec.
YZYH     Q.R. Yuan, Z.H. Zhu, Z.L. Yang, and X.T. He, A&AS, 115, 267, 1996.
         APM positions for IRAS galaxies in Virgo.
        *Standard deviation around 1-2 arcsec.
ZGT      F. Zwicky, H. Gates, and D. Taylor, unpublished ONR Report, 1955.
        *Standard deviation around 5-7 arcsec at a guess.
ZH       F. Zwicky and E. Herzog (CGCG II, p. 319).  Special Coma Cluster map
         and table.
        *Standard deviation around 10 arcsec.
ZTF      Zwicky Transient Facility.  Optical positions for just about 
         anything.  F.J. Masci et al., PASP 131, 995, 2019 and
         https://irsa.ipac.caltech.edu/data/ZTF/docs/ztf_pipelines_deliverables.pdf
        *Standard deviation less than 30 mas for g < 18, rising to about 100
         mas at g = 21.  Since I am using primarily the brighter objects, take
         30 milliarcseconds.

Others as noted in my comments for the objects, though I was able to clean up 
almost all of these thanks to a list of missing sources supplied by Francois 
Ochsenbein in July of 2004 as he was preparing the positions and notes files 
for entry into CDS's catalogue database.

Latest revision:  12 July 2021