Naming the Stars
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.
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
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.
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.
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!)...to 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, V336....to 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.
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".
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