Star Names

Proper Names

The naked-eye stars carry a huge number of names that range from the intimately familiar to the hopelessly obscure, each one having a different reason for being. Vega, the fourth brightest star in the sky, has over 40 different names! Star names are either of ancient origin, of more recent historical origin, or are assigned by astronomical organizations under the umbrella of the International Astronomical Union (the organization of professional research astronomers). No private organizations have the rights to name stars.

The best-known and most-familiar names are "popular names," real names like those used for people. The oldest of all names, proper names are a mixed lot that descend from a variety of ancient (and even modern) languages that relate to the positions or the characters of the stars. Among the oldest are those from ancient Greek. Sirius, for example, means "searing" or "scorching," appropriate for the brightest star in the sky. Procyon comes from the Greek "pro kion," before the dog," as from the northern hemisphere it rises before the "Dog Star," Sirius; Castor honors one of the ancient Greek warrior twins; Arcturus means "bear driver," as this brilliant star follows the Greater Bear around the pole. A smaller number (Regulus, the "little king" in Leo), Polaris, the "pole star" in Ursa Minor) come from Latin.

By far the greatest number, however, hundreds of proper names, descend to us from the Arabic of the middle ages, when the astronomers of the Arabia adopted the Greek constellations from Ptolemy and applied their own names to the stars, most in some way appropriate to the locations of the stars within their parent constellations. "Deneb," for example, means "tail." The name appears in many forms, such as Deneb in Cygnus (the tail of the Swan), Denebola in Leo (the Lion's tail), and Deneb Kaitos in Cetus (the sea-monster's tail). Others were derived from the constellations that the Arabs had made for themselves.

When the Arabic texts were translated back into Latin, these star names were passed down to us, but often in a highly corrupted form that either changed the meaning, or in extreme cases left us with no meaning at all. Other names were mistakenly transferred from one star to another, so that a name might even refer to a different constellation (Greek or Arabic) rather than to the one of the star's actual residence.

Greek Letter Names

To bring order out the chaos of proper names, around the year 1600 Johannes Bayer, in what is now Germany, applied lower case Greek letter names to the stars more or less in order of brightness, which if followed strictly would render the brightest star in a constellation "Alpha," the second Beta," and so on. To the Greek letter name is appended the Latin possessive form of the constellation name. Thus the brightest star in Lyra, Vega (an Arabic proper name), becomes Alpha of Lyra or Alpha Lyrae (where "Lyrae" means "of Lyra.") The brightness rule is commonly violated, however, as Bayer also clearly factored in the position of the star within the constellation, as in Ursa Major, where the stars of the Big Dipper are lettered west to east. As another good example, though Adhara in Canis Major (the Greater Dog) is first magnitude and the second brightest star in the constellation, it received "Epsilon," probably because of its lower (more southerly) position within the starry figure.

With only 24 letters in the Greek alphabet, few stars could receive Greek letter names. Bayer therefore followed the lower-case Greek alphabet with upper case A and then lower-case Roman letters. These are rarely used nowadays, however, and only a few vestiges like "h Persei" (a star cluster in Perseus) survive. Though the number of names is increased by applying numerical superscripts to stars that fall near one another (a string of stars in Orion becoming Pi-1, Pi-2, Pi-3 Orionis, and so on, expressed as superscripts), the system was still limited to the brighter stars, faint naked-eye stars rarely qualifying. Others applied Greek and Roman letters to the later modern constellations. The eighteenth century's Nicholas-Louis de Lacaille was particularly notable for his work in the part of the southern hemisphere that Bayer could not see.

Flamsteed Numbers

To organize more of the naked eye stars, in the eighteenth century John Flamsteed (who created one of the great star catalogues of the time) listed the stars by position (right ascension, the sky's analogue to terrestrial longitude) within the constellation boundaries. Serial numbers applied by Edmund Halley then gave the star's relative location from west to east within the constellation. For example, 1 Lyrae would be the western-most numbered star in Lyra, 2 Lyrae the next, and so on (Vega is 3 Lyrae). In general, first magnitude (and a few special) stars are commonly known by their proper names. Greek-letter names are then used until they run out, and then the Flamsteed numbers. From England, Flamsteed could see only so far into the southern hemisphere, so deep southern constellations have no numbers. The handful of exceptions (30 Doradus in the Large Magellanic Cloud, the globular cluster 47 Tucanae) are vestiges of other systems that did not survive.

Catalogue Names

To include yet more stars, constellations are dropped and the stars are named according to position, generally right ascension, or angle to the east of the Vernal Equinox. (The Vernal Equinox is the point in Pisces where the ecliptic, the path of the Sun, crosses the celestial equator going north and where we find the Sun on the first day of northern spring.) Catalogues fall into two broad categories: general and special interest. The most basic of the general variety is the "Bright Star Catalogue," which serially numbers 9000 naked-eye stars through sixth magnitude from west to east beginning at right ascension zero hours (zero degrees) for the year 1900. (Precession, the 26,000-year wobble in the Earth's axis, changes the right ascensions with time, usually increasing them.) Though now published at Yale, it derives from a catalogue produced at Harvard, so the star names take on the name "HR" for "Harvard Revised." Vega = Alpha Lyrae = 3 Lyrae = HR 7001.

Stars below naked-eye visibility need catalogue names too. The most famed general catalogue for fainter stars, the "Bonner Durchmusterung" (the Bonn Survey), was compiled in Germany in the nineteenth century and lists stars through around tenth magnitude (some 50 times fainter than the eye can see alone). It divides the sky into declination strips one degree wide and then serially numbers the stars from west to east according to the stars' right ascensions (for the year 1855). (Declination is the sky's analogue to terrestrial latitude; it gives the angular separation of a star from the celestial equator.) The catalogue name incorporates the declination. Vega, for example, is also "BD+38° 3238," which means the 3238th star in the declination strip between 38 and 39 degrees north. The BD covers stars to -2 degrees declination (2 degrees south of the celestial equator). The rest of the southern hemisphere is covered by the "Cordoba Durchmusterung" (the Cordoba, Argentina, Survey), or CD. Canopus (HR 2326) is CD- 52°914, or the 914th listed star between declination 52 and 53 degrees south. BD and CD are sometimes combined as "DM" for "Durchmusterung." Precession has now moved many stars out of their original declination strips.

The most commonly used catalogue for fainter (as well as brighter) stars is the Henry Draper (HD) Memorial Catalogue, which serially numbers stars through roughly tenth magnitude to the east of the vernal equinox (according to right ascension in the year 1900) independently of declination. The HD catalogue, while a general tool for star names, is also a specialty catalogue, and was created to list the spectral classes of over 300,000 stars. Vega is HD 172167, Canopus HD 45348.

In the 1960s over ten positional catalogues were combined into the Smithsonian Astrophysical Observatory (SAO) star catalogue. It serially numbers over 250,000 stars (according to right ascensions for the year 1900) to ninth magnitude in 10 degree declination strips from north to south, each strip picking up where the last one left off. Vega is SAO 067174, Canopus SAO 234480. Though it enjoyed some popularity, it is no longer commonly in much use.

The specialty Hipparcos Catalogue is also of general use. The Hipparcos satellite was flown in the 1990s to measure precise distances (through accurate parallaxes) to nearby stars. Over 100,000 stars are listed. Vega is HIC 91262, Canopus HIC 30438.

Beyond these and many other catalogues, fainter stars are named only by coordinates (right ascension and declination) for a specific year. The Hubble Space Telescope Guide Star Catalogue, for example, lists 19 million stars between 6th and 16th magnitude.

Double and Multiple Stars

A huge number of stars are double or multiple, the individuals locked in orbit around each other. The components of very wide doubles that have Greek letter names are often distinguished by applying superscripts to the Greek letters from east to west (as noted in the earlier section on Greek letter names). Zubenelgenubi, Alpha Librae, is a wide double; the western of the two is Alpha-1, the eastern Alpha-2, even though Alpha-2 is much the brighter. Most of these are not physical doubles but line of sight coincidences.

When the stars are close to each other, a system of Roman letters generally applied in order of discovery or of descending brightness (often the same thing) is used. The principal component is "A," the next brightest "B," and so on. Brilliant Sirius is accompanied by a faint white dwarf. The naked-eye star is Sirius A, the dim companion Sirius B. Close companions, particularly planets, are often given lower case letters. If a planet were to be discovered orbiting Sirius A (there is none so far as we know), it would be Sirius Ab, rendering Sirius itself Sirius Aa.

Variable Stars

A great many stars are variable in brightness. The first found, among them Mira and Algol, were bright and had proper or Greek letter names. But as more were discovered, astronomers needed a systematic naming system. Since the last Roman letter in any constellation was "Q," they adopted "R" for the first variable found that did not already have a name, to which was appended the Latin possessive of the constellation name. The first such variable known in Cygnus is thus R Cygni, the first in Aquila R Aquilae. The sequence continued with new discoveries to Z. Finding more, astronomers went back up the alphabet to use double letters, beginning with RR, then going to RS, RT...RZ, then to SS, ST...SZ, TT, TU...and finally down to ZZ.

To accommodate increasing numbers, the system then went to the top of the alphabet, to AA, AB...AZ, BB, BC...BZ, CC...and so on to QQ...QZ, with J left out to avoid confusion. After 334 letter combinations, astronomers just gave up and used "V" followed by a number, V335 Sagittarii following QZ Sagittarii.

Through the names, the astronomers of the past 3000 years have brought order to the seeming chaos of the sky. All the stars you can see even through a relatively large telescope have names. We know them and know where they are.
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