Another of the double stars we often look at, called Albireo, is a chance alignment of two stars that are really quite far apart. Star clusters are concentrated groups of stars. Star clusters like the one shown at here are called globular clusters because the stars form a big ball that is brightest in the middle. Globular clusters are old star groups that formed early in our galaxy's life, long before the Earth. Many are found outside the plane of the galaxy in which most of the other stars are located.
Globular clusters can contain up to more than a million stars.
More random groups of stars are called open clusters . Many open clusters are made up of relatively young stars, formed long after the Earth and our Sun. The Pleiades is the most famous of open clusters. It is known by different names to cultures around the world and has figured prominently in many mythologies. All of the stars in the sky that we can see without a telescope are within our own galaxy, the Milky Way galaxy.