Variable Star (Encyclopedia of Science)
Variable stars are stars that vary in brightness over time. In most cases, these changes occur very slowly over a period of months or even years. In some cases, however, the changes take place in a matter of hours.
The category variable stars encompasses several different types of stars that vary in brightness for entirely different reasons. Examples include red giants, eclipsing binaries, Cepheid variables, and RR Lyrae.
The most common variables, with the longest bright-dim cycles, are red giants. Red giants are stars of average size (like the Sun) in the final stages of life. During the last several million years of its multibillion-year lifetime, a red giant will puff up and shrink many times. It becomes al ternately brighter and dimmer, generally spending about one year in each phase until it completely runs out of fuel to burn.
The apparent variable behavior of a second group of stars, eclips ing binaries, is caused by a very different process. A binary star is a double star system in which two stars orbit each other around a central point of gravity. An eclipsing binary occurs when the plane of a binary's orbit is nearly edgewise to our line of sight (that is, from a viewpoint on Earth). Each star is then eclipsed by the other as they complete their orbits.
A special class of variables, discovered by American astronomer...
(The entire section is 600 words.)
Show us the love and view this for free! Use the facebook like button, or any other share button on this page, and get this content free!free!
Want to Read More?
Subscribe now to read the rest of this article. Plus get complete access to 30,000+ study guides!