This eclipsing binary star runs through a cycle from minimum to maximum and back every 2.87 days, but the drop from peak brightness and subsequent rise lasts only about 10 hours. Algol appears in the northeastern sky after sunset and passes nearly overhead around 11 p.m. local time. Find more nightly observing tips by reading The Sky This Week.
The variable star Algol in Perseus appears faintest at 10:14 p.m. EST tonight, when it shines at magnitude 3.4. If you start watching it immediately after darkness falls, you can see it dim from near its peak brightness (magnitude 2.1) to minimum and then rise back to maximum all in a single night. The triple-star system’s bizarre appearance likely explains why the ancient Greeks associated Algol with the mythological Gorgon, or Medusa.