Variable star

A variable star is a <a href="/facts/Star/euBFuo07">star</a> whose brightness as seen from Earth (its <a href="/facts/Apparent_magnitude/7pCTF1Me">apparent magnitude</a>) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either:

<ul><li>Intrinsic variables, whose luminosity actually changes periodically; for example, because the star swells and shrinks.</li>
<li>Extrinsic variables, whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth; for example, because the star <a href="/facts/Eclipsing_binaries/TYlDe1bD">has an orbiting companion that sometimes eclipses it</a>.</li></ul>
Many, possibly most, stars exhibit at least some <a href="/facts/Oscillation/6vSrm84a">oscillation</a> in luminosity: the energy output of the <a href="/facts/Sun/CadPCVHh">Sun</a>, for example, varies by about 0.1% over an 11-year <a href="/facts/Solar_cycle/QrP4Egea">solar cycle</a>.

Variable star open-in-new

Variable star