ABSOLUTE BEGINNERS

This article featured in the April 2001 Beginners Magazine

CLASSIFYING STARS

 

There are many ways of identifying and classifying stars here are some explanations of the methods used.

All the stars we can see in the night sky are grouped into constellations.  Constellations are not true groups of stars only apparent groups as we see them.  The human mind has a knack of placing almost everything into groups or categories.  Our ancestors associated the stars, that appeared to form groups, with characters from the legends and myths and gave these groups names.  Some look something like the character they are named after but all need a little imagination to make out. 

Some of the brightest stars have a real name like Rigel and Betelgeuse in the constellation of Orion.  Each star also has a label associated with its constellation which takes the form of a letter from the Greek alphabet normally starting at alpha (a) for the brightest.  When there are more stars than the letters in the Greek alphabet numbers are then used or even letters from our alphabet.  So Betelgeuse is called a Orionis and Rigel is called b Orionis although Rigel is actually the brighter of the two.

 

THE GREEK ALPHABET

α	Alpha	ι	iota	ρ	Rho
b	Beta	κ	Kappa	σ	Sigma
g	Gamma	λ	Lambda	τ	Tau
d	Delta	μ	Mu	υ	Upsilon
ε	Epsilon	ν	Nu	φ	Phi
ζ	Zeta	ξ	Xi	χ	Chi
η	Eta	ο	Omicron	ψ	Psi
θ	theta	π	pi	ω	omiga

 

There are of course many more stars than we can see with the naked eye.  When we look through binoculars or a telescope we can see hundreds of stars for every one we saw with the naked eye.  It is quite obvious that if we only used the Greek letters we could never identify all the stars. 

Some stars are identified by a number allocated by the first Astronomer Royal John Flamsteed (1646–1719)  There are many catalogues which use many different methods of listing stars but some of the most well known are the Hubble Star Guide.  Variable stars have special identifications using one or two Roman letters starting at A  through to Z then AA through to ZZ for example RR Lyrae.

There are also true groups of stars varying in size from about ten stars to many billions.  The smallest groups are the Open Clusters which are located within galaxies and can be found all around us in our galaxy, The Milky Way.  These are groups of between ten and a few hundred stars which formed in the same cloud of gas and dust.  Globular Clusters are located as satellite groups around large galaxies.  Galaxies are the largest groups of individual stars in which all known stars are located.  There are many types and shapes of galaxies ranging in size from about a million to a 1000 billion stars for the very largest.

 

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