"Why did not somebody teach me the constellations, and make me at home in the starry heavens, which are always overhead, and which I don't half know to this day?" — Thomas Carlyle, 1880.
In discussing star names and their history, some use must be made of Greek names and letters. Until the twentieth century any well-educated person was expected to be familiar with Latin and Greek, but that cannot be expected today. If you are unfamiliar with Greek letters, you should find a list of them and their names, so you can refer to it when needed; but on this page the first use of an individual Greek letter is accompanied by its name, in parentheses.
When we look at the sky there are no names next to the stars, and no name we assign to a star
truly belongs to it, or says anything about it as a real object. It is merely our way of saying "Look at this star over here, not that one over there." Given the vast numbers of stars scattered across the sky, such appellations are necessary to avoid total confusion; and there is something comforting about knowing what a given star or constellation is called, even if it is just a name established by some sort of historical convention.
An image of the Big Dipper and the stars in its part of the sky
Imagine how difficult it would be to specify one particular star, out of the multitude found in even a small area of the sky, without any way of saying which star you are talking about. (Noel Carboni, apod060317)
Note: It has been brought to my attention that one of the references I used for the following is not to be trusted; as a result, a few of the statements below may not be correct. Until this note is removed, although the discussion below can still serve as an example of the confusion which can be associated with star names, it may be subject to revision.
Common, or "Proper" Star Names
Over the course of history most stars have been given names, to differentiate them. Unfortunately, the same name was occasionally used for different stars, and many stars have been given different names by people living at different times (or of course, in different parts of the world). As an example, the current Pole Star (or North Star) is called Polaris, in acknowledgement of its status. But in ancient Greek (Hellenic) times the Celestial Pole was closer to Kochab than to Polaris, and Polaris was called Phoenice, borrowed from Ursa Phoenice, the Phoenician Bear, the name given to what we now call the Little Bear (or Ursa Minor
) when the constellation was created out of parts of other constellations by Thales, about 600 B.C.E. Later, Ursa Phoenice became κυνόςουρα (Cynosūra), the Dog's Tail, and that name was used for the star for more than a millennium. It is only in the last few hundred years, as precession has brought the Celestial Pole closer and closer to Polaris, that it acquired its present name. Similarly, Vega, one of over forty names used for the brightest star in the constellation of Lyra
, was once used as the name for the constellation itself.
Some of the names which we use for stars and constellations are the names of mythological figures, such as Orion
the hunter, Hercules
the strong-man, and Castor and Pollux, The Twins
. Others describe the star's position in the sky. As an example, Sirius is based on a Greek word meaning 'scorching', because its heat was thought to add to that of the Sun to produce the "dog days" of late summer. It is also called the 'Dog Star' because of its position in Canis Major
, the Big Dog. The name of the bright star to its northeast, Procyon, is based on the Greek 'pro kion', or 'before the dog', because being further north than Sirius it rises before it, even though it is further to the east.
The "common" names of the stars in the Big Dipper.
In 1603, while preparing a "modern" star map, Johann Bayer decided to avoid the confusion associated with having different names for different stars by using the letters of the Greek alphabet to create what we now call "Bayer designations". The brightest stars in a constellation were given letters at the beginning of the alphabet, and fainter stars were given letters further along the alphabet. Thus the brightest star would be α (Alpha), the first letter of the alphabet, the next brightest β (Beta), the second letter of the alphabet, and so on. He did not follow only this rule, however. When, as in the case of the Big Dipper, there are a number of stars of roughly equal brightness, he used their positions to decide which would come first and which would come next. In Orion, which contains two first magnitude
stars, Betelgeuse, which is on "top" (being one of Orion's shoulders), is designated α, and Rigel, which is on the "bottom" (being one of Orion's knees), is designated β, even though Rigel is about thirty percent brighter than Betelgeuse. Similarly, in the Big Dipper, the stars are labeled according to their position, with Dubhe, at one end of the bowl of the Dipper, being designated α, and the other stars being designated β, γ (Gamma), δ (Delta), ε (Epsilon), ζ (Zeta) and η (Eta) in order of position around the bowl and down the handle, even though one of them, Megrez, is substantially fainter than all the others.
The Bayer designation does not consist of only the Greek letter assigned to the star. It also includes the possessive form of the constellation's Latin name. Dubhe is α Ursae Majoris, or "alpha of Ursa Major", while Betelgeuse is α Orionis, or "alpha of Orion". On maps only the Greek letter is shown next to the star, because the constellation is inferred from the overall position in the sky, or indicated by an outline of the area covered by the constellation, and the name of the constellation somewhere inside that outline. In tables, the Greek letter is combined with a three-letter abbreviation of the constellation name, so that Dubhe is α UMa, and Betelgeuse is α Ori. Similarly, Polaris is α UMi or α Ursae Minoris, meaning that it is one of the brightest or most important stars in Ursa Minor, while Kochab, which is equally bright but no longer serves as the Pole Star, is β UMi or β Ursae Minoris.
The Bayer designations of the stars in the Big Dipper.
Alcor, which has no Bayer designation, is indicated by its Flamsteed number.
In the late 1600's John Flamsteed extended Bayer's idea, using numbers instead of letters (in a sense Bayer was numbering them as well, since the letters of the Greek alphabet were used as counters as well as letters). Instead of just numbering the brighter stars as Bayer did, Flamsteed assigned numbers to all the naked-eye stars (that is all the stars visible in a dark sky without optical aid). However, instead of using low numbers for brighter stars and high numbers for fainter stars, which is what Bayer usually did, Flamsteed numbered the stars according to their right ascension, so that the westernmost naked-eye star in a constellation was assigned the number 1, the next star to the east of that in the same constellation was assigned the number 2, and so on.
(many more examples and methods of naming to follow)
Variable Star Names
(far more to be added later, but basically, the first variable-brightness star discovered in Orion is called R Orionis, the second variable star discovered in Gemini is S Geminorum, the third variable star discovered in Auriga is T Aurigae, and so on. Once individual letters are all used up, double letters are used; so for example, we could have a star called RU Lupi in Lupus, or one called TV Ceti in Cetus, if enough variables were discovered in those constellations)
Catalog Numbers and Positional Designations
(far more to be added later, but for instance there are objects in a catalog called the New General Catalog that are called NGC 1, NGC 2, NGC 3 and so on, objects in a catalog created by Charles Messier called M1, M2, M3 and so on, objects in a catalog created by Halton Arp called Arp 1, Arp 2, Arp 3 and so on, and on and on. And nowadays, with billions of stars and other objects in computerized catalogs, it is not unusual to simply specify an object by its position on a particular date, such as J2000 012345.6+012345, meaning the object with the position RA 01 23 45.6, Dec +01 23 45 according to the position of the Pole at the start of 2000 CE.)