variable star
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A variable star is a star whose brightness changes over time as seen from Earth. These stars matter because their brightness patterns help astronomers measure cosmic distances and understand what's happening inside stars.
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Comparison of VLT-SPHERE images of Betelgeuse taken in January 2019 and December 2019, showing the changes in brightness and shape. Betelgeuse is an intrinsically variable star.
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) 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: