Variable Stars

Stars appear to shine with a constant light; however, thousands of stars vary in brightness. The brightness that a star appears to have (apparent magnitude) from our perspective here on Earth depends upon its distance from Earth and its actual intrinsic brightness (absolute magnitude.) The behaviour of stars that vary in magnitude (brightness) - known as variable stars - can be studied by measuring their changes in brightness over time and plotting the changes on a graph called a light curve.

Measuring and recording the changes in apparent magnitude and drawing the resulting light curves will allow you to begin to unravel the stories of the often turbulent and always exciting lives of variable stars.

There are four main classes of variable stars. Within the intrinsic group of variables there are two classes: pulsating and cataclysmic. Within the extrinsic group there are two classes: eclipsing binary and rotating stars.

Pulsating Variables are stars that show periodic expansion and contraction of their surface layers. Pulsations may be radial or non-radial. A radially pulsating star remains spherical in shape, while a star experiencing non-radial pulsations may deviate from a sphere periodically.

Cataclysmic variables (also known as Eruptive variables), as the name implies, are stars that have occasional violent outbursts caused by thermonuclear processes either in their surface layers or deep within their interiors.

Eclipsing Binary Stars are binary systems of stars with an orbital plane lying near the line-of-sight of the observer. The components periodically eclipse one another, causing a decrease in the apparent brightness of the system as seen by the observer.

Rotating stars show small changes in light that may be due to dark or bright spots, or patches on their stellar surfaces (?starspots?). Rotating stars are often binary systems.

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