International Comet Quarterly

ICQ: Recommended (and condemned) sources for stellar magnitudes

Below is a list that observers may use to evaluate whether the source(s) that they are contemplating using for visual or V stellar magnitudes are recommended or not. Unfortunately, many errors have been found over the years in the both the individual variable-star charts of the AAVSO (ICQ code AC) and the AAVSO Variable Star Atlas (code AA); those variable-star charts were designed for the purpose of tracking the relative variation in brightness of individual variable stars, and they frequently are not adequately aligned with the proper magnitude scale. The new Hipparcos/Tycho catalogues have had new codes implemented (see below).

New additions (and changes in categories) will be made to the following list as new information reaches the ICQ.

                        MAGNITUDE-REFERENCE KEY

               Second-draft recommendation list, 1997 Dec. 1.
                  Updated 2007 April 20 and 2017 Oct. 4.

NOTE:  For visual magnitude estimation of comets, NEVER USE SOURCES for
 which the available star magnitudes are only brighter than the comet!
 For example, the SAO Star Catalog is very poor for magnitudes fainter
 than 9.0, and should NEVER be used on comets fainter than mag 9.5.  The
 Tycho catalogue should not be used for comets fainter than mag 10.5.
 (Even CCD photometrists should be wary of using bright stars for very 
 faint comets; it is always best to use comparison stars within a few
 magnitudes of the comet when doing CCD photometry.)

NOTE:  It is highly recommended that users of variable-star charts also
  specify (in descriptive notes to accompany the tabulated data) the
  specific chart(s) used for each observation; this information will be
  published in the ICQ.  Also, observers are urged to not be careless
  about the use of secondary references for comparison-star magnitudes:
  specifically, if using a secondary source (such as amateur software
  containing compilations of professional star-catalogue data, or even
  professional catalogues such as the SAOC containing magnitudes from
  other catalogues), one should note both the primary and secondary
  sources CLEARLY.

***  Recommended Sources:
Old   New
Key   Key          Source  [+ location in ICQ where first introduced]
---   ---    ----------------------------------------------------------------
 A     A     Charts or Atlas of the A.A.V.S.O.  (NOTE:  codes AA or AC should be
                should be used instead)  [ICQ 3, 47]
       AA    A.A.V.S.O. Variable Star Atlas  [ICQ 4, 6]
       AC    Charts of the Amer. Assn. of Var. Star Observers 
               (specific chart should be specified)  [ICQ 4, 7]
       AE    Planetary magnitudes from the American Ephemeris and Nautical
                Almanac (for use with bright comets) [ICQ 4, 105]; also star
                magnitudes from Astronomical Almanac
 F     AG    Astronomisches Gesellschaft Katalog  [ICQ 2, 6]
       AH    G. D. Roth's Astronomy:  A Handbook, p. 534 (chart of the Pleiades)
                [ICQ 6, 64]
       AN    Comparison-star sequences as published by M. Beyer in articles in
                Astron. Nachrichten.  Following are some excerpts from a letter
                that Beyer wrote to Dennis Milon on 1970 Sept. 16:
                "From 1930 to 1946 all observations are given in magnitudes
                of the Revised Harvard Photometry (Harv. Ann. 50 or Pickerings
                Northern Polar Sequence).  Later I reduced all my observations
                (variable stars and comets) to the Internat. Photovisual
                System.  The very reliable magnitudes in Harv. Ann. 50, 54,
                and 74 can be reduced to the Ipv-System by using
                         Pv(Mt. Wilson) = Harv. + Korr. + fC
                given in Mt. Wilson Contributions 88.  Most stars with
                magnitudes brighter than 7.5 are given in the Harv. Catalogues.
                Pickerings Durchmusterungszonen in Harv. Ann. 70 show
                systematic errors by more than 0.3 mag.  Therefore all the
                fainter stars have been measured by myself applying a
                Graff-wedge-photometer and for comparison the IPv Northern
                Polar Sequence.  As these photometric measurements have to be
                made only under good atmospheric conditions and in higher
                altitudes of the stars, it lasts often a longer time before
                the total magnitudes of the comets can be derived."  
       AO    USNO (S)A1.0 catalogue R magnitudes, from the first editions
                of this catalogue; not recommended because magnitudes may
                be off by 0.5 mag or more due to photographic calibration
                errors, but CCD astrometric comet observers are using them
                due to convenience; see more information on the World Wide
                Web at
                  [see also ref. UO]
       AP    Atlas Photometrique des Constellations (1948), by Antoine Brun
                (has stars to mag 7.5 labeled with Harvard photometry
                magnitudes)  [ICQ 5, 24]
       AS    AAVSO chart for M81 (NGC 3031) in Ursa Major, which was closely
                scrutinized and revised during April and May 1993 as a result
                of SN 1993J.  The revised sequence, which was published in the
                April 1993 issue of the ICQ, has a good sequence for the range
                10.3 < V < 15.5.  [ICQ 15, 60; 15, 102]
 Z     AT    Arizona-Tonantzintla Catalog (publ. in July 1965 Sky & Telescope)
                [ICQ 2, 6; 4, 8]
       AU    ASAS-3 V magnitudes, available from website:
      , and
                click on "Search: V-band" under "Photometric Catalog"
                (it is recommended that specific sequences and/or website
                URLs be mentioned in descriptive data) [ICQ 25, 160]
       BC    Boss Catalogue
 B     BD    Bonner Durchmusterung (Argelander et al.)  [ICQ 2, 59; 4, 63]
       BR    V magnitude sequence for stars in the Coma cluster of galaxies
                including Abell 1656 (Boerngen and Richter 1978, A.N. 299, 177)
       BS    Johnson V photometry by Brian Skiff at Lowell Observatory, with
              data given at the World Wide Website URL
              because website material may be transient, the ICQ policy for
              use of this source is to give additional information in the
              descriptive information accompanying the published tabulated
              data in the ICQ.
       C     Photovisual magnitudes from "Cape Photographic Catalogue for
             1950.0", in Annals of the Cape Observatory, Vols. 17-22.  
             [ICQ 9, 142]
       CA    M44 standard sequence as published in Henden and Kaitchuck's
             Astronomical Photometry (1982, New York:  Van Nostrand Reinhold),
             pp. 301-302.  [ICQ 9, 99]
       CC    Carte du Ciel, Paris (Astrographic Catalogue?)  [ICQ 10, 35]
       CD    Open star cluster NGC 225 (R.A. = 0h43m.8, Decl. = +61 47', equi-
             nox 2000.0) photometry; star chart with mag-
             nitudes given (9.2 < V < 16.0) as published in Visual Astronomy
             of the Deep Sky (see ref. 'CL', below), p. 250.
       CE    Open star cluster NGC 1647 photometry (8.5 < V < 16.4), in Visual
             Astronomy of the Deep Sky, p. 252 (see ref. 'CL', below).
       CF    Open star cluster NGC 2129 photometry (11.2 < V < 16.1), in Visual
             Astronomy of the Deep Sky, p. 254 (see ref. 'CL', below).
       CG    Open star cluster NGC 2422 (M47) photometry (7.7 < V < 14.3), in
             Visual Astronomy of the Deep Sky, p. 256 (see ref. 'CL', below).
       CH    Open star cluster NGC 6494 (M23) photometry (9.3 < V < 13.9), in
             Visual Astronomy of the Deep Sky, p. 258 (see ref. 'CL', below).
       CI    Open star cluster NGC 6823 photometry (9.4 < V < 16.0), in Visual
             Astronomy of the Deep Sky, p. 260 (see ref. 'CL', below).
       CJ    Open star cluster NGC 6910 photometry (9.9 < V < 14.9), in Visual
             Astronomy of the Deep Sky, p. 262 (see ref. 'CL', below).
       CK    Open star cluster NGC 7031 photometry (11.2 < V < 16.5), in Visual
             Astronomy of the Deep Sky, p. 264 (see ref. 'CL', below).
       CL    Photometry by Hoag et al. (1961) from one of the open-star-cluster
             charts as published in Visual Astronomy of the Deep Sky, by Roger
             N. Clark (Cambridge Univ. Press, 1990), pp. 250-266.
       CM    Photovisual and photoelectric-V magnitudes from Cape Mimeograms
             (Royal Observatory, Cape of Good Hope).  [ICQ 9, 142]
       CN    Open star cluster NGC 7235 photometry (8.7 < V < 16.4), in Visual
             Astronomy of the Deep Sky, p. 266 (see ref. 'CL', above).
       CO    UBV photometry for 39 stars in the range 11.7 < V < 18.7, from
             "A New Stellar Standard Sequence in the Comet Cluster of Galax-
             ies" (F. Boerngen and N. Richter 1978, Astron. Nach. 299, 117)
       CR    V magnitudes of 13 stars surrounding NGC 3627 (M66), as given by
                 Ciatti and Rosino (1977, A.Ap. 56, 62).  The range in V is
                 13.8-16.9, and the stars are fairly red.  [ICQ 11, 30]
       CS    Catalogue of Stellar Identifications (1979, Strasbourg).  Large
             compilation of many catalogues.  For information, see F.
             Ochsenbein et al. (1981), A.Ap. Suppl. 43, 259, and Ochsenbein
             (1974), A.Ap. Suppl. 15, 215.  The visual magnitudes with colons
             (:) should be avoided if possible.  [ICQ 10, 35]
       D     Dutch Comet Halley Handbook (E. P. Bus)  [ICQ 7, 96]
       E     One of Everhart's 3 Selected Area charts (1984, Sky Telesc. 67, 28)
       EA    Selected Area 51:  From Everhart (1984, Sky Telesc. 67, pp. 28-30).
       EB    Selected Area 57:  From Everhart (1984, see EA, above)  [ICQ 7, 51]
       EC    Selected Area 68:  From Everhart (1984, see EA, above)  [ICQ 7, 51]
       FA    V photometry by Harold Ables, U.S. Naval Observatory, Flagstaff,
               "Region No. 6", unpublished (stellar V magnitude range 11.1-15.8
               photoelectric and 13.7-21.6 electronographic).  [ICQ 9, 99]
       FD    R magnitudes of M13 stars as published in "A photoelectric BVRI
               sequence in the field of the globular cluster NGC 6205 (M13)",
               by D. Forbes and P. C. Dawson (1986), PASP 98, 102-103.
       FG    from variable star charts published in *A Field Guide to the Stars
               and Planets*, by D. H. Menzel and J. M. Pasachoff (part of the
               Peterson Field Guide Series); charts by Wil Tirion for SS Cyg
               (visual mag 5.1-11.4), R CrB (7.5-12.6), Algol (2.9-5.5), beta
               Lyr, and Mira (3.5-9.2) are given on pages 158-161 of the second
               edition and pages 198-201 of the third ed. (magnitude source is
               not specified, but probably AAVSO)
       GA    Guide Star Photometric Catalog - I, in Astrophysical Journal
               Supplement Series, Volume 68, Number 1 (1988 September).
               Contains nearly 1500 stars with V magnitudes and convenient
               finder charts throughout the sky.  [ICQ 10, 124; 15, 60]
       GP    [apparently same as 'HE'; see below]
 G     GR    Groombridge (1838, rev. 1905, Greenwich Obs.)  [ICQ 3, 15]
       HC    photographic R-band magnitudes from Hubble Space Telescope
               Guide Star Catalogue  [ICQ 145]
 D     HD    Henry Draper Catalog (Harvard Coll. Obs. Annals)  [ICQ 2, 39]
       HE    Harvard E Regions (declination -45 deg), Kron-Cousins V photometry
               for nine fields; stars range generally between 7 < V < 16 
               (Graham 1982, P.A.S.P. 94, 244)  [ICQ 10, 124]               
       HI    Hipparcos Input Catalogue (C. Turon et al. 1992, European Space
               Agency Special Publication SP-1136; derived V magnitudes
               (118,000 stars brighter than mag 13, with the distribution
               peak around V = 9); see also HJ
       HJ    magnitudes in the Hipparcos photometric system, Hp (see code
               HI, above); peak of Hp is closer to true visual than to
               Johnson V, though it has a long red wing
       HK    H_p magnitudes from the Hipparcos Catalogue (ESA SP-1200).
       HN    Arne Henden's photometric sequences, which can be downloaded
               from his computer at 
               (and especially via R. Bouma at 
      and via M. Simonsen
               at -- but specific
               sequences should be specified in descriptive data [ICQ 26, 8]
       HP    Harvard Photometry (Harvard College Obs. Annals)  [ICQ 4, 8]
 H     HR    Harvard Revised Photometry (H.C.O. Annals)  [ICQ 1, 42; 4, 8]
       HS    V magnitudes from Hubble Space Telescope astrometric catalogue
               of stars on compact disk  [see ICQ 15, 60]
       HV    Johnson V magnitudes from Hipparcos Catalogue, ESA SP-1200.
       JH    Jet Propulsion Laboratory's Horizons website (for planetary
               magnitudes  []  [ICQ 29, 14]
       JT    Cousins VRI magnitudes of stars in M67 (M. Joner and B. Taylor
               1990, PASP 102, 1004)
       L     Landolt V Photoelectric Sequences (AJ 78, 959)  [ICQ 6, 37]
       LA    Landolt photoelectric sequences (1992, AJ 104, 340)
       LB    Landolt (1983, AJ 88, 439 and 853) sequences as published by
               Christian Buil in ASTRONOMIE CCD (1989, Societe d'Astronomie
               Populaire), p. 261
       LC    Landolt (1975, PASP 87, 379) magnitude sequence for 33 stars
               near V1057 Cyg (V magnitude range 5.5-15.5)
       LD    *Lietuvos Dangus 2007* (Vilnius, 2006), p. 171
               (an annual Lithuanian publication)  [ICQ 29, 14]
 L     LN    Lampkin's Naked-Eye Stars  [ICQ 2, 6]
       LM    V magnitudes from "A Visual Atlas of the Large Magellanic Cloud",
                by Mati Morel (1983), Rankin Park, New South Wales  [ICQ 10, 67]
       MC    Carlsberg Meridian Catalogue (1989).  Volume 4.  La Palma.
                More than 50,000 stars with visual magnitudes down to V = 13;
                do not use stars with magnitudes given to less than 0.01 mag.
       ME    V photometry by Tedesco, Tholen, and Zellner (1982, A.J. 87, 1585);
                mag range 6-13  [ICQ 8, 77]
       MK    V magnitudes for M67 in LE GUIDE PRATIQUE DE L'ASTRONOMIE CCD
                P. Martinez and A. Klotz 1994; Adagio press), p. 270
       ML    V magnitudes on chart of Large Magellanic Cloud by Mati Morel
                              (apparently same as LM)
       MM    V magnitudes on chart of Small Magellanic Cloud by Mati Morel
                              (apparently same as SM)
 U     MP    McCormick Photovisual Sequence (Univ. of Virginia)  [ICQ 3, 15]
       MS    From "McCormick Photovisual Sequences", by C. A. Wirtanen and
             A. N. Vyssotsky (1945, Ap.J. 101, 141-178).  [ICQ 9, 142]
       MT    Visual magnitudes of stars in M67 as published by B. E. Schaefer
                (1989, SKY TEL. 77, 332); after work by Racine and Gilliland.
       MV    From Publ. Leander McCormick Obs., Vol. VI, Part II, pp. 201-306
             ("Magnitudes and Coordinates of Comparison Stars in Regions of
             Long-Period Variables, by S. A. Mitchell, 1935) or Vol. IX, Part
             V, pp. 59-88 ("Sequences for Fifty Variable Stars", by Mitchell
             and C. A. Wirtanen, 1939).  [ICQ 9, 142]
       NH    North Polar Sequence as published by Henden and Kaitchuck (1982,
                Astronomical Photometry, NY: Van Nostrand Reinhold), p. 305.
       NN    NGC 2129/6531/1342 cluster photometry, in Publ. U.S.N.O. Vol.
                XVII, parts VII, VIII (1961), pp. 406, etc..  [ICQ 8, 130]
 O     NO    U.S.N.O. Photoelectric Photometry Catalogue  [ICQ 2, 6; 4, 8]
 N     NP    North Polar Sequence (publ. by the A.A.V.S.O.); 3 charts showing
                stars w/ useful range mv = 5.0 and fainter  [ICQ 1, 17; 3, 7]
       NS    "Magnitudes and Colors of Stars North of +80 ", by Seares, Ross, 
                 and Joyner (1941, Carnegie Inst. Publication 532)  [ICQ 4, 80]
       OB    magnitudes for faint cluster stars from S. C. Odewahn, C. Bryja,
                 and R. M. Humphreys (1992), PASP, 104, 553 [used by
                 Spacewatch beginning 1999 Sept. 29, replacing FA; ICQ 123]
       OH    From listing of bright stars in Observers' Handbook, R.A.S.C.
                 [ICQ 7, 51]
       PA    M45 sequence, Johnson & Mitchell (1958, Ap.J. 128, 31)  [ICQ 8, 77]
       PB    Pleiades chart in Sky and Telescope 70, 465 (1985).   [ICQ 8, 77]
       PC    Pleiades sequence, Henden and Kaitchuck (1982, Astronomical Photo-
                metry; N.Y.:  Van Nostrand Reinhold), pp. 298-300  [ICQ 8, 130]
       PD    "Photometrische Durchmusterung:  Generalkatalog", by G. Mueller and
                P. Kempf (1907), in Publ. Astrophysikalischen Observatoriums zu
                Postdam No. 52 (Vol. 17); B.D. stars to mag 7.5  [ICQ 10, 35]
       PI    IC 4665 sequence as found in Henden and Kaitchuck (1982,
                Astronomical Photometry, New York:  Van Nostrand Reinhold),
                pp. 302-304.  [ICQ 10, 35]
       PK    From the Soviet Program for Comet Halley; Dr. Klim Churyumov,
                Kiev University, describes the method as follows (edited):
                Comparison stars were noted on the Palomar Sky Survey prints;
                the visual magnitudes of these stars were determined by
                comparison with standards stars from the galactic cluster
                NGC 2129 (V magnitudes taken from the paper by Hoag et al.
                in Publ. U.S.N.O., Second Series, Vol. XVII, Part VII, pages
                406 and 518, 1961).  The visual magnitudes were determined
                by use of the formula mv = V + 0.16(B-V).
       PL    star(s) & sources quoted for photoelectric data, but difference
                (comet - comparison-star) > 4.5 mag  [ICQ 10, 35]
       RA    Annual Ephemeris of the Royal Astronomical Society of Canada (not
                recommended, even for bright comets)  [ICQ 5, 64]
       RB    "Photoelectric Magnitudes and Colours of Southern Stars",
             A. W. J. Cousins and R. H. Stoy (1963), in Royal Observatory
             Bulletin No. 64 (Royal Greenwich Obs.), Series E3, pp. E101-E248.
                [ICQ 9, 142]
       RC    "Standard Magnitudes in the E Regions", A. W. J. Cousins and R.
             H. Stoy (1962), in Royal Observatory Bulletin No. 49 (Royal
             Greenwich Obs.), Series E2, pp. E1-E59.  [ICQ 9, 142]
 S     S     Smithsonian Astrophysical Obs. Star Catalog  [ICQ 1, 17; 4, 9]
       SA    M67 sequence by R. E. Schild (1983, PASP 95, 1021), Kron-Cousins
                        magnitudes  [ICQ 10, 35]
       SC    Sky Catalogue 2000.0 (Sky Publishing; stars of magnitude 
                        V < 8.1)  [ICQ 4, 62; 4, 105]
       SD    V magnitudes of members of the globular cluster M15 in the range
                        13 < V < 22 [and also nearby field stars for 40 stars
                        of mag 7.64, 10.42-11.15, and 12.9 < V < 18.8],
                        by A. Sandage (1970, Ap.J. 162, 841)
       SE    V magnitudes of 134 stars of the II Persei Association (stars of
                        spectral types A and B, mag range 5.1-11.4;
                        C. K. Seyfert et al., Ap.J. 132, 58).  [ICQ 11, 30]
       SK    Brian Skiff's compilation of magnitudes as part of the LONEOS
                project (Lowell Observatory), appearing via Internet access
                (as of 9/25/01, containing about 33000 stars throughout
                the sky from some 600 published sources -- mostly professional
                astronomy journal articles); though magnitude range goes
                from V = 7.4 to V = 22.9, only about 40 stars in this list
                are brighter than mag 9.0 (but generally a good source of V
                magnitudes for stars fainter than mag 10 or 11)
       SM    V magnitudes from "A Visual Atlas of the Small Magellanic Cloud",
                by Mati Morel (1989), Rankin Park, N.S.W., Australia
 K     SP    Skalnate-Pleso Atlas Catalog (Atlas Coeli Cat.)  [ICQ 2, 6; 4, 10]
       SS    Various regions covering declination -60 deg to +10 deg, with
                stars having general range 12 < V < 24; Stobie et al. (1985),
                Astron. Astrophys. Suppl. Ser. 60, 503
       ST    list of star magnitudes compiled by Brian Skiff and posted at
                (submitted by R. D. Schwartz, who presumed this to be a
                culled list of the brighter standards from Landolt's lists)  [ICQ 145]
       SW    Four half-degree fields with finder charts and UBV photometry,
                range 10 < V < 15 (except field IV, which has a gap between
                11.5 < V < 13.5), published by W. Saurer et al. (1992) in
                Astron. Astrophys. Suppl. Ser. 93, 553.  The four fields
                average about 40 stars each, roughly centered at the following
                R.A. and Decl. (B1950.0):  I, 1h27m, +58.2 deg; II, 3h24m,
                +45.2 deg; III, 7h15m, -10.1 deg; IV, 21h31m, +50.2 deg.
       TA    Comparison-star magnitudes from "The Amateur Sky Survey"
                (TASS), which has data available at the website URL
        [ICQ No. 133]
       TB    Supernova Search Charts, by G. D. Thompson and J. T. Bryan, Jr.
                (1989, Cambridge University Press)
                [specific chart should be specified]
       TG    CCD magnitudes on the Thuan-Gunn system; comparison standard
                 stars in Thuan and Gunn (1976, PASP 88, 543).
       TI    Tycho Input Catalogue; more than three million stars brighter
                 than V = 12.1 prepared for the needs of the Tycho mission
                 (Hipparcos satellite; see D. Egret et al. 1992, Astron.
                 Astrophys. 258, 217); available upon request from the
                 Strasbourg Data Center (France; e-mail address
       TJ    Tycho Catalogue Johnson V magnitudes from ESA SP-1200.
       TK    Tycho-2 Catalogue (Hog et al. 2000, A.Ap., in press);
                 NOTE:  *only* Tycho-2 V_T magnitudes (labeled VT)
                 from the *main* catalogue should be used.  The
                 supplements contain a mix of V-like magnitudes
                 from the original Tycho catalogue and should not
                 be taken from here.
       TS    Field of 13 stars (R.A. 22h02m, Decl. -19.1 deg, equinox 1950.0),
                 V magnitudes with finding chart, 9.7 < V < 19.2, by Tritton
                 et al. (1984), MNRAS 206, 843-847.
       TT    Tycho/Hipparcos Catalogue V_T magnitudes from ESA SP-1200.
 V     V     Variable star charts from recognized sources  [ICQ 1, 42]
                 (specific chart should be specified)  
       VB    Variable star charts of the British Astr. Assn.  [ICQ 4, 64]
                 (specific chart should be specified)  
       VF    Variable star charts of the A.F.O.E.V. (France)  [ICQ 4, 64]
                 (specific chart should be specified)  
       VG    Japanese variable-star charts edited by K. Gomi and based on
                charts drawn by Y. Kawanishi, publ. in 1970 by Koseisha Co.
                as a spiral-bound book; its preface states that the magnitudes
                of comparison stars are taken from Harvard Annals (Vols. 37,
                50, 54, and 57) and from Skalnate Pleso II (Atlas Coeli).
                Akimasa Nakamura, who reported this reference to the ICQ,
                says that his comparison of Gomi charts with AAVSO charts
                show that the comparison-star magnitudes are very close to
                each other.
       VN    Variable star charts of the R.A.S. of New Zealand  [ICQ 4, 64]
                 (specific chart should be specified)  
       W     International Halley Watch (IHW) version of an unspecified
                AAVSO chart  [ICQ 7, 96]
       WA    Special IHW version of AAVSO chart for SU Tauri  [ICQ 7, 96]
       WB    Special IHW version of AAVSO chart for CZ Orionis  [ICQ 7, 96]
       WC    Special IHW version of AAVSO chart for Y Tauri  [ICQ 7, 96]
       WD    Special IHW version of AAVSO chart for V Tauri  [ICQ 7, 96]
       WE    IHW version of AAVSO chart for X Sextantis  [ICQ 8, 130]
       WF    IHW version of AAVSO chart for S Sextantis  [ICQ 8, 130]
       WG    IHW version of AAVSO chart for SX Leonis  [ICQ 8, 130]
       WH    Unspecified IHW charts  [ICQ 8, 44] 
                   (this code should not be used)
       WW    B.A.A. Charts as published in the IHW Observers' Manual [ICQ 8, 44]
 Y     Y     Yale Bright Star Catalogue  [ICQ 1, 42; 4, 8]
       YF    Yale Bright Star Catalogue, fourth edition (should now be used
                instead of earlier editions)
       YG    Yale Bright Star Catalogue, fifth edition
       YZ    Yale Zone catalogue 


 T       UA     Atlases Borealis, Eclipticalis, Australis  [ICQ 2, 6]
         UB     USNO-B1 catalogue magnitudes (B1 and B2, or R1 and R2)  [ICQ 151]
 C, CP   UC     Cape Photographic Catalogs  [ICQ 1, 42; 4, 63]
         UD     Naval Observatory Merged Astrometric Dataset (NOMAD), a new
                  astrometric catalogue that compiled data from several
                  catalogues including Tycho-2, UCAC-2, and USNO-B1.0 (i.e.,
                  some good data and some not-so-good data).  [ICQ 151]
         UL     Specific comet or planet mentioned as magnitude reference, but
                     comparison object not above horizon at same time as comet
                     OR no catalog listed  [ICQ 7, 51]
 M       UM     Magnitudes of galaxies, nebulae, etc.  [ICQ 2, 6]
 R       UN     Norton's Atlas  [ICQ 2, 39; 4, 62]
         UO     USNO-A2.0 catalogue R magnitudes; not recommended because
                magnitudes may be off by 0.5 to 2 full magnitudes or more
                due to photographic calibration errors, but CCD astrometric
                comet observers are using them due to convenience
                  [see also ref. AO]
 I, Q    UP     Any standard photographic atlas (e.g., Falkauer, Stellarium)
                     [ICQ 3, 15; 2, 59]
 J, RC   UR     Revue des Constellations  [ICQ 5, 24; 5, 64]
         UU     UCAC2 astrometric star catalogue; magnitudes with
                     uncertainty estimated as +/- 0.3, intended for
                     identification only (bandpass spans V to R)  [ICQ 29, 14]
         US     Skalnate Pleso Atlas  [ICQ 7, 51]
         UV     USNO-A2.0 catalogue used to extract blue and red magnitudes,
                  then converted to "V" magnitudes through the following
                  formula derived by T. Kato (Kyoto Univ.) by comparing two
                  variable-star fields (SW UMa and IR Gem):
                    V = r + 0.375 * (b - r); communicated by A. Nakamura
 X       UX     Specific stars quoted, no catalogue given  [ICQ 2, 39]

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