Why Are Some Stars Brighter than Others?
Stars may appear very bright because they are bright, or because they are close to the Earth. The stars are not all at the same distance from us. Some stars are closer and some are farther away. The closer a star is to us, the brighter it will appear.
Stars are actually great balls of glowing gases – their brightness depending upon their size and temperature. Larger stars usually shine more brightly than smaller stars do. So, how bright a star appears in the night sky depends on its size and how far away from us it is.
Astronomers measure the brightness of stars by magnitude. A bright star may be zero or first magnitude. Stars that are just visible to the naked eye are called stars of the sixth magnitude. Each magnitude is 2 ½ times brighter than the next magnitude. Therefore, a first-magnitude star is 100 times as bright as a sixth magnitude star.