Eclipsing Binary Stars

A binary star is a star system in which there are two stars orbiting each other. The eclipsing effect of an eclipsing binary star system is seen when one star passes in front of the other from Earth’s perspective. The passage of one star in front of the other creates a sudden significant light decrease than the light emission from the system before. Because of this light decrease, eclipsing binary stars can be identified through a plotted light over time graph, otherwise known as a light curve. Eclipsing binary stars have unique light curves in which there is consistent light and then sudden drops of light emission, and this unique light curve allows observers to notice when they have found an eclipsing binary star system.

What Information Does a Light Curve Give?

A light curve is a plot of the light emission of a star over time, and in the case of an eclipsing binary star system represents the orbital period of one companion star around the other. Every time a dip of light occurs on the plotted graph, it means that one star eclipsed the other from the viewpoint of Earth and therefore has completed one orbit with reference to Earth. The light dips on the light curve have a deeper minimum light value when the brighter companion star is eclipsed and a shallower minimum light value when the dimmer star is eclipsed.

An example of the light curve of an eclipsing binary star system. The sudden drops of light occur when one star passes in front of its companion star from Earth’s perspective.

Algol, also known as the “Demon Star”, is the most famous eclipsing binary star. It is located 93 light years away in the constellation Perseus, which can be seen during the fall months.