Nomenclature of Astronomical Objects

1. Stars:
 
        a.    Proper Names:  These have long been used in many cultures to identify a few of the brightest stars, e.g., Vega,
               the brightest star in the constellation Lyra which is conspicuous in the northern sky of summer and early fall, is
               the fifth brightest star (not counting the sun) in the entire sky.

        b.    Bayer designation:  These were assigned by Johann Bayer in 1603, in his star atlas Uranometria.  Bayer often
               designated the brightest star in a constellation α + the genitive form of the constellation name, the second
               brightest, ß + . . . , etc.  However there are many exceptions to this rule.  In particular, since Bayer had no
               precise way of measuring a star's brightness, the fainter members of a constellation with Bayer classifications
               are only roughly in order of brightness.  After exhausting the 24 lower case letter of the Greek alphabet, Bayer
               then used the lower-case Latin letters, then upper-case Latin letters.  A good example of an exception to Bayer's
              general rule is Ursa Major, wherein the seven bright stars of the Big Dipper asterism bear the first seven Greek
              letters, α through η, ordered from the outer lip of the bowl to the tip of the handle.  Vega = α Lyrae is an example
              where the more common rule applies.

        c.   Flamsteed designation:  These were assigned by John Flamsteed early in the 18th century.  (They were first
              published in 1712 in his catalog Historia Coelestis Britannica which was published by Edmond Halley and Isaac
              Newton in 1712 without Flamsteed's approval!)  Flamsteed's designation differs from Bayer's in two respects;  (1)
              numerals are used rather than Greek letters, and (2) numerals are assigned in order of increasing right ascension
              (because of precession that rule is now violated in a few cases), e.g., Vega = α Lyrae = 3 Lyr.  There are 2554
              stars with Flamsteed designations.

        d.   Other catalog designations:  There are many of these.  For example Vega is designated as BD +38°3238 in the
              Bonner Durchmusterung, a German catalog of ~320 000 stars (virtually all stars north with δ > -2° with m_v < 9.5),
              published in the mid-nineteenth century (given positions are with respect to the equinox of 1855.0) (Vega is the
              3238th cataloged star, in order of increasing right ascension with a declination in the range 38° < δ < 39°).  In the
              Henry Draper Catalogue, a catalog of spectral classifications published ~1920, 225 300 stars with magnitudes
              brighter than 9.0 are listed.  Vega = HD 172 167.  In the Bright Star Catalog, aka HR Catalog, Vega = BS 7001 =
              HR 7001.  In the Smithsonian Astrophysical Observatory Catalog, Vega = SAO 67164, etc.

        e.   Objects which are studied but have never been identified by a catalog number can be identified in the literature for
              other prospective observers by publishing precise coordinates for the equinox position of a specified date together
              with a finding chart or photograph.

2. Variable Stars:

        Brighter variable stars are designated by a strange scheme somewhat similar to the Bayer scheme which observes
        the rules which follow:  If a star has a Bayer Greek-letter designation, then no new designation is assigned.
        Otherwise its designation depends upon the order in which its variability is discovered.  The first discovered variable
        star in a constrellation is R affixed to the genitive form of constellation name, second discovered = S (genitive form of
        constellation name), third = T (״), . . . , ninth = Z (״), tenth = RR (״), eleventh = RS (״), . . . , eighteenth = RZ (״),
        nineteenth = SS (״) , . . . , twenty-sixth = SZ (״), twenty-seventh = TT (״), . . . , fifty-fourth = ZZ (״), fifty-fifth = AA (״),
        . . . , seventy-ninth = AZ (״), eightieth = BB (״), . . . , one-hundred-third = BZ (״) , . . . , three-hundred-thirty-fourth =
        QZ (״), three-hundred-thirty-fifth = V335 (״), three-hundred-thirty-sixth = V336 (״), . . . , etc.  (Note that the letter "J"
        is never used and in the utilized double-letter combinations, the second letter is never alphabetically before the first
        letter.)

3. Extended Objects (diffuse nebulae, galaxies, globular star clusters, open star clusters, planetary nebulae)

        a.  Proper names, e.g., Orion nebula

        b.  Messier Catalog Number:  Charles Messier was a French comet hunter who published a list of extended fuzzy
             objects for comet hunters to avoid in its final form the year 1781.  At that time the list included 103 objects, but it
             was expanded to 110 by his associates, e.g., Orion nebula = M42.

        c.  New General Catalog number:  This catalog was compiled in the 1880s by J. L. E. Dreyer.  It contains 7 840
             objects.  It was supplemented by two editions of the Index Catalog (IC) in the next two decades, e.g., Orion nebula
             = NGC 1976.

        d.  Extended Objects which are studied but have never been identified by a catalog number can be identified in the
             literature for other prospective observers by publishing precise coordinates for the equinox position of a specified
             date together with a finding chart or photograph.  Positions are especially important since extended objects of low
             surface brightness may be completely invisible to an observer looking through a telescope.  Neighboring stars can
             be utilized for guiding purposes when "observing" such an object.