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How do eclipsing variable stars such as Algol change in brightness?
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Star
Stars in the open cluster NGC 290, as seen by the Hubble Space Telescope.
An eclipsing variable star, such as Algol, changes in brightness because it is a binary star system in which the orbital plane is oriented edge-on toward Earth. As the two stars revolve around their common center of mass, they periodically pass in front of one another from our perspective, causing one star to eclipse the other.123
These rhythmic fluctuations in the total light of the system are recorded in a light curve, which displays the changes in brightness over time. The light curve typically features two distinct minima:23
- Primary Minimum: A deep decrease in brightness occurs when the brighter star is eclipsed by the dimmer companion.23
- Secondary Minimum: A shallower decrease in brightness occurs when the brighter star passes in front of the dimmer one.23
In the case of Algol, the system’s apparent visual magnitude fluctuates between 2.1 and 3.4 over a period of approximately 2.87 days.43