Herculean Lists

By the 19th century all these naming efforts were falling far short of the mushrooming need. Telescopes were revealing stars by the hundreds of thousands, every one of them an individual crying out for its own identity.

In 1859 the German astronomer F. W. A. Argelander at Bonn Observatory began measuring star positions with a 3-inch refractor to compile a gigantic list, the Bonner Durchmusterung (Bonn Survey). The BD eventually included 324,188 stars as faint as about magnitude 9.5. Argelander and his successors divided the sky into thin, 1°-wide declination bands wrapping around all 24 hours of right ascension. Stars within each band were numbered in order of right ascension; constellations were ignored. Thus Vega's designation BD +38°3238 means it was the 3,238th star (counting from 0 hours right ascension) in the zone between declination +38° and +39°.

The original BD covered just over half the sky, from the north pole to a declination of –2°. A later southward extension, the SBD, marched down to declination –23° to garner another 133,659 stars. The Cordoba Durchmusterung (CD or CoD) completed the job, picking up 613,953 more on its way to the south celestial pole. All in all, Durchmusterung, or "DM," names were bestowed on a grand total of 1,071,800 stars.

The BD, with its detailed star charts and its reliable, well-checked list of positions, remained an essential everyday tool of working astronomers for nearly a century. Durchmusterung designations are still sometimes encountered. The magnitudes of stars in these catalogs, however, are notoriously unreliable by modern standards. Most were merely quick eyeball estimates.

Variable stars have a naming system all their own. This too was instigated by the energetic Argelander. He denoted the first variable star found in a constellation by the capital letter R with the genitive of the constellation name (since the previous letter, Q, was the farthest Bayer had gone in Roman star-lettering). The next variable would be named S, and so on to Z. After Z came RR, RS, and so on to RZ, then SS to SZ, on up to ZZ. If a variable already had a Greek letter, Argelander left it alone.

But new variable stars kept getting discovered! After ZZ, astronomers decided to go to AA, AB, and on to AZ (omitting J since in some languages it could be confused with I), then BB to BZ, on up to QZ.

Even these 334 designations proved insufficient for the variables in some crowded constellations. Rather than start an even more awkward three-letter system, astronomers ruled that further variables in a constellation would simply be designated V335, V336, and so on forever. It was a wise move. By 2003 the highest numbered variable was V5112 Sagittarii. Read more...