GALAXIES AND QUASARS
I learned the following information from an article at the website of thinkquest. A galaxy is a group of many stars that is spinning through space. Galaxies come in a variety of types based on their shape, groups they may be in, and a number of other attributes. There are five main types of galaxies, classified according to their shape: ellipticals, spirals, lenticular, barreled spirals, and irregular shapes. Elliptical galaxies are ellipses in shape.
One astronomical object that was often mistaken for a galaxy in the past is a quasar. A quasar is an object that is not a star but which radiates an enormous amount of light. The light of a quasar fluctuates over extremely short periods of time, often in a matter of seconds. This shows that quasars are not very big, because it takes light a long time, measured in years, to travel through an entire galaxy. A rule of thumb is that the faster an object shifts its light emission, the smaller it must be. A quasar can emit as much light as a whole galaxy with billions of stars in it. Scientists today generally believe that a quasar is actually an extremely huge black hole.
Star populations of an area have two classifications. The two types of star population are Type I and Type II. Type I includes blue giant stars and blue supergiant stars. Type I includes the arms of spirals and irregular galaxies. Type II are elliptical, lenticular and the nuclei of spirals. Type II includes red giants, subgiants, and subdwarfs.