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Glossary term: variable star

Description: A variable star is a star that shows marked changes in brightness over time to observers on Earth. There are several possible physical mechanisms that can lead to variability. Some stars, such as Cepheids or RR Lyrae, are unstable and pulsate, changing their size and brightness periodically. Other stars can eject bright material that increases the overall observed brightness ("eruptive variables"). Stars called cataclysmic variables or novae show a sudden increase in brightness followed by a return to their previous level. Behind this is a pair of stars, with matter from one flowing onto the other, and igniting in a nuclear fusion reaction as soon as a certain threshold is reached. Other stars appear variable because they are rotating, showing us alternately a brighter and a less bright side, or because there are really two stars orbiting each other, with the brighter partner occasionally hiding behind his less bright companion (an eclipsing binary).

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Term and definition status: This term and its definition is still awaiting approval

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".