Algol, the Devil’s Star: Why This “Blinking” Star Changes Brightness

Algol, located in the constellation Perseus, is also known as the “Devil’s Star” or “Ghoul.” In the fall, you can find it in the northeastern sky after 9 p.m., near Cassiopeia and Andromeda. In Greek mythology, Algol represents the “blinking eye” of the gorgon Medusa. But what makes stars appear to twinkle—and why does Algol seem to blink?

How Algol’s Brightness Changes

Algol is a triple-star system, with two of its three stars orbiting each other. This eclipsing binary system regularly changes from a bright magnitude of +2.1 to a slightly dimmer magnitude of +3.4 about every three days.

As one star passes in front of the other, it temporarily blocks some of its light. The result is a predictable dip in brightness—like Medusa’s “blinking eye.” This light curve, created with data from NASA’s Transiting Exoplanet Survey Satellite (TESS) mission, shows these regular obscurations.

How to Observe Algol’s Dimming

From interactive charts to data plots, there are many resources available to help calculate Algol’s dimming, or minimum brightness. Use whichever method works best for you.

Algol’s brightness is similar to that of the nearby star Almach, also known as Gamma Andromedae. You can compare the two stars with binoculars or a small telescope to track Algol’s changing brightness.

Find the Witch’s Head Nebula

Between Eridanus and Orion lies an eerie silhouette illuminated by the star Rigel. Known as IC 2118, the Witch’s Head Nebula is a reflection nebula located about 900 light-years from Earth.

Reflection nebulae are difficult to see with the naked eye, especially at this distance, because they depend on light from nearby stars to become visible. The Witch’s Head Nebula cannot be seen without optical aid, but under dark skies it can be viewed with a telescope featuring a very large aperture and low magnification.

Astrophotographers, whether they use traditional equipment or smart telescopes, can capture this unforgettable outline within hours, depending on their equipment and sky conditions. And what is a witch without a broom? The Witch’s Broom can be found in the Western Veil Nebula in the constellation Cygnus.

More Spooky Stargazing Tips

Want more ideas for enjoying the season? Read our guide to community stargazing: Trick or Treat: Sidewalk Astronomy!