Multiplying Catalogs

The next great, widely used star list to appear after the BD was the Henry Draper Catalogue of stellar spectra, which Annie J. Cannon compiled in the 1910s at Harvard College Observatory. It includes 225,300 stars numbered in simple order of right ascension. More were added later in the Henry Draper Extension; these bear HDE numbers. Any star with an HD or HDE designation is guaranteed to have had its spectrum measured.

Meanwhile another catalog had been issued at Harvard: the Revised Harvard Photometry of 1908, which sought to provide accurate magnitudes for the brightest 9,110 stars to about magnitude 6.5. Stars in this catalog bear HR numbers. Even now the HR list remains the basis of the modern Yale Bright Star Catalogue, which remains widely used for its detailed information about naked-eye stars.

Another star-numbering system used today is the SAO designation. This refers to the Smithsonian Astrophysical Observatory Star Catalog (1966), which also was produced (with companion star charts) on Harvard's campus. This catalog gives very accurate positions for 258,997 stars down to about 9th magnitude, though coverage is spotty for the fainter ones. The SAO stars are numbered by right ascension within 10°-wide declination bands. They cover the entire celestial sphere. SAO numbers supplanted the once widely used GC designations, from the General Catalogue of 33,342 Stars by Benjamin Boss (1937).

One of the largest modern star lists is the Hubble Space Telescope Guide Star Catalog. The GSC lists positions generally good to nearly 1 arcsecond and magnitudes accurate to a few tenths for 18,819,291 objects. The GSC's brightest entries are 9th magnitude (brighter stars couldn't be used by Hubble's guiding cameras); the faintest are typically about 13th or 14th magnitude, sometimes 15th. Of this total, 15,169,873 are listed as being stars; most of the remaining 3.6 million objects are small, faint galaxies. Most have never been examined by human eyes; machines measured their properties off of photographic plates. A typical individual in this list is GSC 1234 1132, a 13.3-magnitude luminary in Taurus. The first four digits specify one of 9,537 small regions of the sky; the last four give the object's serial number within this region.

More recently, the Hipparcos and Tycho Catalogues have largely supplanted the GSC for the brightest 1 million stars. TYC and especially HIP stars had their positions, magnitudes, distances, and motions measured to high accuracy by the European Space Agency's epoch-making Hipparcos satellite in the 1990s.

In the last decade much vaster star catalogs have been coming online — such as the Sloan Digital Sky Survey (SDSS), the infrared Two-Micron All Sky Survey (2MASS), and the U.S. Naval Observatory's gigantic and standard-setting UCAC. And of course, no end is in sight.

P.S.: Name-It-Yourself Stars Are a Hoax!

People sometimes call Sky & Telescope to ask about one of the several competing companies advertising that they will name a star after you or a loved one for about $50. You get a pretty certificate and some papers. Is this for real, we are asked?

No. The certificate is a "novelty item" only. With just as much validity, you can step outside on a clear night, choose any star you like, and name it for anyone you want. For free.

We know lots of amateur astronomers who have done this for their spouses or children. To one of Sky & Telescope's editors, Iota Ursae Majoris is "Lucy's Star," and Zeta Hydrae is "Andrew's Star." Why not?

Why pay some commercial outfit to mediate your personal life? Even a fancy certificate, if it appeals to you, can be printed with shareware for a lot less than $50. One of the companies advertises that it keeps the names in a Swiss bank vault, as if that means something. If that appeals to you, you can put a piece of paper with a star name in your own bank's safe-deposit box. But why bother?

Sometimes planetariums "sell" stars on their domes to help raise needed funds. They are careful to tell donors that the certificate they get denotes a contribution to a worthy institution, not the purchase of a real star name. If you insist on paying someone else to pretend to name a star, this is a more worthwhile way to do it.