Robert Burget, age 11, of Williamsport, Penna. far his question:
How many different stars are there?
There are more than two billion earth people, every one different from all the rest. But if intelligent insects arrived from Mars, we earthlings would see that our likenesses outnumber our differences. So it is with the stars. All have features in common, but each star has a few differences.
In our Galaxy, we are told, there are about 100 billion stars. When we see the Milky Way, we get an edgewise view of the pinwheel which is our horue in the heavens. There are many millions like it scattered throughout the vast ocean of space and the total number of stars is uncountable. Each star almost certainly has some little feature to make it unique, but the list of likeness shared by all the stars is also uncountable.
Every star is a controlled nuclear furnace of burning gases. Its energy is released because changes take place in the nuclei of its atoms. All stars are hot and radioactive. All star material is gaseous and many atoms are stripped of their electrons and become ions. Most star material is hydrogen and the remaining elements are some of those from which our earth is made.
Stars have a long list of features in common, but they have differences. There are baby stars,, teenagers, adults and old timers. There are giants and dwarfs and some are ten times hotter than others. Stars come in different colors and contain different assortment elements. The differences and likenesses have been used to classify the star population.
Astronomers have sorted the stars into seven main classes, with a number of subclasses and a few odd balls. Class M includes the red giants. They are cool stars of about 5,500 degrees and big enough to swallow a sizeable chunk of our Solar System. K class stars are red orange and about 7,000 degrees. They are somewhat smaller than the giants and someof their gases are metallic elements.
The stars in class G are golden yellow, of medium size and around 11,000 degrees which is medium temperature for a star. In this medium, middle of the road group of stars we find our own glorious sun. Class F stars are yellow white, about 13,500 degrees hot and there are metallic elements among their gases. Class A stars are dazzling white, teaming with hydrogen and about 20,000 degrees hot. The blue white stars in class B are about 36,000 degrees and the blueish stars in class 0 see the at temperatures above 55,000 degrees.
Star classification is a very rough and ready method for sorting the starry population into recognizable groups. Every star in a class is not exactly like all its classmates. There are borderline stars between the classes and odd balls that do not fit into any of these man made classes.