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STAR NAMES AND CONVENTIONS
Where do star names come from? Who named the constellations? What about nebula and Deep Sky Objects? What do all the numbers and letters stand for?

Catalogues


The Babylonians were known to refer to the constellations as long ago as 2000 BCE; Homer refers to constellations in his writings around 700BCE. The cuneiform star list in the Mulapin series dates from 687 BCE, but the first recorded catalogue of stars was written by Hipparchus around 135BCE. Hipparchus also derived the Magnitude scale of describing stars brightness. We say it was around that time because no copies of it exist, however Ptolemy, in his work Mathematica Syntaxis refers to Hiparcus' catalogue of 850 stars in 48 constellations. In 960 AD Al Suphi's book of fixed stars was published. It is probably because of this heritage of learning and writings (Ptolemy's works were still in use until the 16th century) that the constellations are named after Greek figures, but most of the named stars have Arabic names. The Arabs were great astronomers and brought their own work and the work of the Greeks to western Europe. These works considered mostly the northern skies, and therefore did not contain much information regarding the southern hemisphere, many of the southern constellations being named later.


The letters of the Greek alphabet, used for the Bayer designations.
In 1602 Johan Bayer published his catalogue of 1200 stars, and introduced the use of Greek letters of the alphabet to describe the stars of a constellation in descending order of magnitude (the Bayer designation). Shortly after this Tyco Brahe's 1000 star catalogue was published posthumously by Johannes Kepler as the 'Rudolphine Tables' (in honour of the Holy Roman Emperor: Rudolf II). John Flamsteed was the first Astronomer Royal, and set up the Royal Observatory at Greenwich. His catalogue was published in 1725, and contained 2,935 stars. It introduced numerical (Flamsteed) designations for the stars. There followed a large number of detailed and specialist catalogues from Herschel, Messier and Armagh Observatory (the Index Catalogues). In 1880, the New General Catalogue was commissioned by the Royal Astronomical Society numbering 7,840 non-stellar objects. In 1922 the International Astronomical Union first met to standardise constellation naming and boundaries, which they did in 1930. In 1989-93, the ESA's Hipparcos mission flew and the resulting catalogue (the Hipparcos and Tycho catalogues) listed 2.5 Million stars.


Star Names

Today, star names, or common names are a convenience. Only the brightest stars are named (or their names are the only ones we can remember!). These Arabic names however are well loved and well known and most star charts and computerised telescoope systems will list them.The IAU is the only organisation that can designate stars and constellation boundaries, but obviously professional astronomers are more likely to work with catalogue numbers or star coordinates than named stars. The IAU maintains a list of 'common names' for the brighter stars.

That said, the constellation and star names are very useful to amateurs for finding our way about the night sky. So learning the names of the sign posts is a useful exercise!

Tips on observing constellations:
• A finger held out at arm's length is approximately 1 degree across
• A fist held out at arm's length is approximately 10 degree across
• The principle larger constellations (Ursa Major, Orion, and Cassiopeia) are 20 degrees across their longest parts.

The Pole star


Taking the Plough as our starting point; the two end stars (Merak and Dubhe) are the pointer stars. If you draw a line through them pointing north, you will come to Polaris (the Pole star). Polaris is approximately 1 degree from the NCP which is towards Kocab (at present). Pherkad and Kocab are the next brightest stars in the constellation of Ursa Minor (little bear), in the South East of England, the sky clarity can be estimated from the number of stars that can be seen in Ursa Minor.

The spring stars


In the spring, the constellation of Bootes (the hunter) will appear towards the east. The first star to be visible will be Arcturus, which can be identified as a bright yellow star. If you follow the handle of the plough around in and 'arc' you will find Arcturus.

The Summer Triangle


Looking south in August you will see three bright stars that we group together as the Summer Triangle (remembered as DAVE to its friends). Deneb, Altair and VEga are the brightest stars of 3 different constellations.
Deneb in the constellation of Cygnus (the swan) sits right on the Milky Way, and on clear nights the band of gas and dust between us and the outer spiral arm (the Cygnus Rift) can be seen. The Milky Way extends down through the constellation of Aquila (the eagle), Altair is its brightest star. Vega in the constellation of Lyra (the lyre) is a tiny constellation, but it includes the deep sky object M57 (the Ring Nebula) between its bottom two stars.

The Winter Stars


In the clearer nights of the winter, the constellation of Orion will be prominent in the south. Using Orion as our signpost, we can draw imaginary lines as pointers to the main constellations. If you hold your hand outspread at arm's length, Orion will span over your outspread thumb and little finger. If you go up following a line from Saiph (Orion's left foot) up through the centre of the constellation a little over twice the height of Orion you will come to the bright star Capella in Auriga (the charioteer). Drawing another line from Rigel (Orion's right foot) through Betelgeuse about the same distance you will come to the star Castor, part of the constellation of Gemini (the twins). Drawing a line through Orion's belt downwards, you will come to the brightest star in the sky; Sirius, part of the constellation of Canis Major (the Big Dog).

Further information

For further information on the night sky see:-
» Sky Map and Guide
» Guide to the Night Sky



Article by Noel Clark

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