Characteristics of Stars

There are hundreds of billions of stars in the universe. Stars are classified by mass, size, and temperature. Our Sun is considered to have an average mass. Other stars can be huge, having 100 or 200 times--or even more--mass than our Sun; while there are other stars that are very small with half the mass of our Sun, or even less. Generally speaking, the larger a star is, the shorter its life span tends to be.

New stars usually start out in a nebula, a large cloud of gas and dust. The gas and dust may be denser in some regions in the nebula. Gravity pulls the gas and dust into hot clumps, called protostars. If the protostar gets hot enough, nuclear fusion may take place and a new star is born. The type of star that is born depends on its mass.

Our sun seems massive enough to be the largest star in the galaxy. This is because it is the only star in our solar system meaning it is the closest star to Earth. Classified as a yellow dwarf star, our Sun is average in terms of size, temperature, and brightness. Some stars are much smaller, larger, cooler, or hotter. Our Sun will live an average length of time, which, for a yellow dwarf star, is about 10 billion years. Currently, it is about 4.5 billion years old.