Many people have never had the opportunity to look up at a truly clear night sky and appreciate the full splendour of the heavens. This is due to the light pollution produced from our cities and urban areas. As well as the tremendous waste of energy due to radiating so much light pointlessly up at the sky, this light gets reflected and dispersed by particles in the air giving the sky a dirty orange glow. This makes it impossible to see the fainter stars, the impressive glow of the milky way (our own galaxy) or other faint objects such as the Andromeda galaxy (our nearest neighbouring galaxy).
Photo courtesy of Andre Clayden - Springbrook Research Observatory
Even in very remote areas where there are still spectacular views of the heavens our eyes do not reveal the full beauty of the night sky. Although we can see differences in brightness are eyes are not sensitive enough to detect the different colours of the stars that are studded throughout the heavens. Photographic techniques however do reveal these colours and this gives us our first clue to the differences between the stars in our night sky.
To make sense of these differences has been something of a detective story for astronomers, however they have been able to determine that the differences we see are due to differences in mass and the different ages of the stars. In this section we will look at the birth, life of death of stars and at how a stars characteristics depend on its mass. This in turn will explain the range of different types of stars that are visible in the night sky.