About Constellations

Long before television and computer games people had to amuse themselves in other ways. One thing they did was to look up at the sky and play join the dots, giving names to groups of stars which appear close to each other in the sky.

As well as for religious reasons there were many practical applications of being able to find easily and identify different stars in the sky including timekeeping and navigation. A good example of this is the ability to find North using Ursa Major.

This shows the brightest and most recognisable stars in Ursa Major, The Great Bear, including the two pointer stars.

Sirius is the brightest star in the sky in the constellation of Canis Major. (At the time the pyramids were built it was the pole star!) The easiest way to find Sirius however is by using the much more recognisable constellation of Orion.

For this course you need to be able to recognise and draw Ursa Major, Orion, Taurus, Cassiopeia and four other constellations in the Northern or Southern hemispheres.

Draw Taurus, Cassiopeia and four other constellations. Label the brightest stars in each.

There are several websites where you can find this information. I recommend www.astrofilitrentini.it/mat/costell_eng.html

So, is a constellation a group of stars next to each other? Absolutely not. The fact that they appear next to each other in the sky is just because of our viewpoint on Earth. They may be many hundreds of light years apart. Bear in mind also that they may appear roughly the same brightness (their apparent magnitude) but a dim star relatively close to us may appear the same brightness as a much brighter star further away.

An observer may also mistake a planet for a star changing the appearance of the constellation it is passing through.

Some stars are actually grouped together in space, such as the Pleiades.

NASA

Below is a chart showing the constellation Cepheus.

Notice that the stars have been given letters of the Greek alphabet. Alpha is the brightest (2.6), beta the second brightest (3.3) etc. They may also have names, e.g. alpha Cephei is called Alderamin. The lines on the graph denote Declination (in degrees) and Right Ascension (in hours, minutes and seconds). e.g. for alpha Cephei, Alderamin its coordinates are   RA: 21h 18m 34.73s  Dec: +62° 35' 07.9"