Variable star

Most stars are of nearly constant luminosity. Our own Sun is a good example of one which goes through relatively little variation in brightness (usually about 0.1% over an 11 year solar cycle). Many stars, however, undergo significant variations in luminosity, and these are known as variable stars. Variable stars may be either intrinsic or extrinsic.

Extrinsic variables

Eclipsing binaries

Extrinsic variables have variations in their brightness, as seen by terrestrial observers, due to some external source. One of the most common reasons for this is the presence of a binary companion star, so that the two together form a binary star. When seen from certain angles, one star may eclipse the other, causing a reduction in brightness. One of the most famous eclipsing binaries is Algol, or Beta Persei.

Related Topics:
Binary star - Eclipse - Algol

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Planetary eclipses

Stars with planetary systems may also show brightness variations if their planets pass between the earth and the star. These variations are much smaller than those seen with stellar companions, and are only detectable with extremely accurate observations.

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Rotating stars

Stars with sizable sunspots may show significant variations in brightness as they rotate, and brighter areas of the surface are brought into view.

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