Naming the Stars
(Stellar Nomenclature)

Most people know that the brightest stars have some old and unusual names.  But what about the rest of them?  They have 'names' as well, otherwise how would astronomers be able to describe which one they are talking about to a colleague?  All the stars we can see in the sky and those fainter than we can see have a 'name' even if it is just a number designation in a catalogue.  This month we'll take a look at the common systems used to label and identify stars today.

Proper Names
The first and oldest system is known by the term of  Proper Names.  These are the brightest 200 or so stars that were given a name by ancient peoples.  Betelgeuse, Sirius, Vega and Antares are all examples of Proper Names.  There are some instances where the same name was given to different stars.  Some names have also varied greatly over time and with civilisations.  A large majority of the Proper Names that remain are Arabic in origin.  This is because after the collapse of the Roman empire and the ancient Greek civilisations the Arabs became the most scientifically literate peoples of the Dark Ages.  They translated many texts from Greek and Latin into their own language, sometimes assigning their own names as they studied the heavens and this was the form this knowledge was passed on back to the Europeans as the Renaissance began.  This is why so many star names start with the prefix "Al-", it is Arabic for "the".  If you delve even further into star lore you will quickly find that each culture gave the most prominent stars different names, but the ones we use today are mostly of European and Middle Eastern origin. 

The Bayer System
This is the next most prominent system is used to name the stars we can see with the naked eye.  Johann Bayer was an uranographer (someone who maps the stars) from Germany, who published a set of ornate star charts in 1603.  This was the first complete set of charts known and it may also be interesting to note that it was just before the appearance of the first telescopes.  He introduced a system where for each recognised constellation he used the Greek alphabet to label the stars from the brightest to the least brightest.  The brightest star was then called alpha, the second brightest beta, the third brightest gamma, and so on.  When describing a star in a particular constellation the Latin genitive case was used, as in those times Latin was the language of science and all the constellations were known by a Latin name.  So Regulus, the brightest star in Leo, is also known as alpha Leonis.   Just to make it confusing, if you look closely at some charts you'll notice that the brightest star in some constellations is not labeled alpha.  For some cases there is a reason.  The four constellations Carina, Vela, Puppis and Pyxis were once part of a much larger constellation known as Argo Navis.  Argo Navis was such a large constellation that in the 1750's it was split into the four smaller constellations we know today but their Bayer letters were not reassigned.  So the alpha and beta stars are in Carina, gamma belongs to Vela.  Below is the Greek alphabet as written on star charts.   Many modern astronomy books will give you the genitive case of the 88 modern constellations, so we wont include them here in the present time.

The Greek Alphabet

a alpha i iota r rho
b beta k kappa s sigma
g gamma l lambda t tau
d delta m mu u upsilon
e epsilon n nu j phi
z zeta x xi c chi
h eta o omicron y psi
q theta p pi w omega

Flamsteed Numbers
John Flamsteed, the first Astronomer Royal compiled a catalogue of 3000 stars to help determine longitude at sea.  It published posthumously in 1725.  For each constellation he numbered the stars in Right Ascension from East to West.  If two or more stars had the same R.A. then the sequence ran from north to south.  Today some of the fainter stars which didn't receive a Bayer letter are known by their Flamsteed Number.  Hence that odd name for a such a well known globular cluster (which appears star like to the naked eye), 47 Tucanae. 

Roman letters
In some constellations Roman letters were used if there wasn't enough of the Greek alphabet to label all the stars.  The lowercase letters a to z were then used and if still more were required the capital letters A to Q were used.  The capital letters from R onwards were eventually used to name variable stars. 

Variable Stars
The first variable star noticed was Mira the Wonderful, in Cetus the Whale, in 1596.  Now we know of thousands!  Variable stars have their own labeling system that is not quite so simple as those previously mentioned.  The first variable that was found in a constellation was labeled R (that's always a capital R, not a lower case r), the second S, the third T, and so on to the end of the alphabet.  After this the sequence becomes double letters, starting with RR, RS, RT and so on to RZ; then it starts again at SS, ST and so on to ZZ.  Then the sequence starts at AA, AB... (and so on!) QZ, with the letter J omitted from use.  At the end of all this if there are more variable stars they receive the label V335, how ever many variable stars there may be.  Some of the bigger constellations centered over parts of the Milky Way have hundreds of variable stars.

Catalogue Numbers
If you peer more closely at a set of detailed charts you will notice that there are even more numbers and labels.  These are catalogue designations and there are literally hundreds of different catalogues for covering a huge range of objects.  Don't be overwhelmed by this avalanche of data!  There are a couple of catalogues that are widely used by amateur astronomers and these are the ones you should make yourself familiar with.  The others you may meet in passing or if you have a particular interest.  The stories behind some historical catalogues are fascinating in themselves.  You can even make your own catalogue of your favourite objects, if you wish! 

The two catalogues that are most prominent on amateur star charts are the Messier Catalogue and the New General Catalogue, otherwise known as the NGC Catalogue.  The New General Catalogue was complied by J.L.E.  Dreyer in 1864 when the number of existing catalogues made it impractical to check for  new discoveries quickly.  Again, it is a list of the brightest 7800 deep sky objects in the sky and it includes the Messier and Herschel Catalogues, among others.  An object belonging to this catalogue is only marked  with the catalogue number, so all those three or four digit numbers floating about on the charts are actually NGC numbers!  For example the Helix Nebula in Aquarius will be marked on a chart with just the numbers "7293" not "NGC 7293".



 © Stargazers Astronomy  2001.