Eclipsing Binary Stars ‒ Algol

The bright stars of Algol are located in the Perseus constellation. Although Algol appears as a single star to the naked eye, astronomical observations have revealed that it is actually a triple star system. This system consists of two stars, Algol A and Algol B, which orbit closely around a common center of gravity, and a third star, Algol C, which orbits around the pair. The Algol system is aligned so that when viewed from Earth, the stars Algol A and B periodically eclipse each other. This occurs because the plane of their orbit almost perfectly aligns with our line of sight. Algol A and B complete one orbit around their center of gravity every 2 days, 20 hours, and 49 minutes. As a result of these periodic eclipses, the brightness of Algol, as seen from Earth, varies regularly. These changes in brightness are so pronounced that they can be observed with the naked eye, earning Algol the designation of an "eclipsing binary star." It is also one of the first variable stars, which are stars whose brightness fluctuates over time, to be identified. The animation of the Algol system depicts the orbital movement of Algol A and B. The difference in mass between the two stars means the center of gravity is significantly shifted toward the heavier star. The "Line of Sight from Earth" illustrates how the inclination of the entire system appears to an observer on Earth's surface.