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10/28/2021 – Ephemeris – The spookiest star in the sky

October 28, 2021

This is Ephemeris for Thursday, October 28th. Today the Sun will be up for 10 hours and 21 minutes, setting at 6:36, and it will rise tomorrow at 8:17. The Moon, at last quarter today, will rise at 12:31 tomorrow morning.

We are getting down to the spookiest time of the year, with Halloween on Sunday, so it’s time to talk about the spookiest star in the sky, Algol the Ghoul or Demon Star. It’s in the constellation of Perseus the hero, now rising in the northeastern sky. The constellation itself looks like the Greek letter pi, or like the cartoon Roadrunner with its long legs. Algol is the second brightest star in the constellation, near the Roadrunner’s leading foot. That’s where the eye of the severed head of Medusa, that Perseus is carrying. It’s still winking, once every 2 days and 21 hours*. Tonight it will be in the deepest part of its wink at 8:43 pm. It will take about three hours to recover its usual brightness. I recall that the ancient Chinese weren’t fond of that star either.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.

* More specifically, 2 days, 20 hours, 49 minutes on average and altered by Earth’s changing distance from the star due to its orbit of the Sun.


Algol Finder Animation

Algol Finder Animation for around 8 pm in the later part of October and early November (7 pm after the EST time change on the first Sunday in November). Created using Stellarium and GIMP.

Algol is an eclipsing binary star, where one star eclipses the other.

Eclipsing Binary Star

Animation of an eclipsing binary star like Algol. Credit: Wikimedia Commons h/t Earth and Sky

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