A Wink From The Demon Star


Use the Pleiades and Capella to point you to Algol, the "Demon Star" — Stellarium

The weather doesn’t look good around here for the next two nights but maybe it’ll be better by you. If so, you have the chance to witness a star go from bright to dim right before your eyes.

The star is Algol, otherwise known as the "Demon Star", in the constellation Perseus the Hero. The name derives from Arabic and likely refers to its mysterious fadings every 2.87 days. Algol is actually a very close double star whose companions revolve around one another. When the bigger, fainter one gets in front of smaller, brighter one, we see the star change in brightness. Astronomers describe the Demon Star as an eclipsing binary because one star partially eclipses the other.


Two stars do the "demon’s" work — Bob King / News Tribune

The change is very easy to see with the naked eye. Typically, Algol is as bright as nearby Mirfak (see map above) but during an eclipse, it dramatically fades to look like the fainter stars in Perseus.

Tonight you’ll find Algol by making a big right triangle with the bright star Capella and the Pleiades or Seven Sisters cluster. The eclipse lasts about 10 hours but Algol will be dimmest around 10 o’clock Central Time. Check at 8:30-9 p.m. when’s it’s still pretty bright. Then look again at 10, and the difference should be obvious. Use Mirfak for comparison. By 11:30 p.m., Algol will have mostly recovered.

It’s a wonderous thing that you and I can stand in our soggy yards on an April night and watch a solar eclipse happening 93 light years away. Let the show begin.