When we look at the night sky with the unaided eye, or even through optical telescopes, we see bright stars and faint stars, and in some cases we see distinct differences in colour. But what our eyes see, is only a tiny fraction of what is called EM-radiation.
Star light, Star bright.
Modern interpretation of the zodiac
by Bechnokid at http://bechnokid.deviantart.com.
In this module we will discuss some aspects of EM-radiation that are of importance to Astronomy, and explain how these aspects are telling us most of what we know about stars and other luminous objects in the Universe.
But first some basics.