This Week’s Night Sky: Stellar Ghoul Haunts Halloween Skies

This Week’s Night Sky: Stellar Ghoul Haunts Halloween Skies
The moon guides the way to a creepy crab, and a monster’s eye appears to wink at Earth.
Hunter’s Moon.  Just after local sunset on Monday, October 26, look for the silvery full moon rising in the east, located within the large but faint zodiacal constellation Pisces, the fishes. Native American tribes called this full moon the Hunter’s Moon because it appears during the time when hunters are preparing for winter.

For an added observing challenge, use binoculars to hunt down the ice giant Uranus about 10 degrees to the right of the moon, about equal to the width of your fist at arm’s length.

Bull’s Eye.  After nightfall on Thursday, October 29, the waning gibbous moon and the bright orange star Aldebaran create a stunning pair in the constellation Taurus. From North America, the cosmic duo will appear separated by less than 1 degree, meaning you could easily cover both with your thumb held at arm’s length.

Skywatchers in Europe and northern Asia will witness an even more dramatic sky event, with the moon occulting, or going in front of and covering, the 66 light-year-distant star.

Crab Nebula.  Late night on Friday, October 30, the waning gibbous moon will be parked just beneath one of the brightest supernova remnants in the entire sky, an expanding cloud that sits about 7,000 light-years from Earth.

Just above the moon is Zeta Tau, one of the stars that mark the tips of Taurus's long horns. The star acts as a convenient guidepost to the famed Crab Nebula, the remains of a supernova recorded by Chinese astronomers in A.D. 1054.

Look for the faint Crab Nebula, also known as Messier 1, approximately 1 degree above Zeta Tau and 5 degrees above the moon—slightly less than the width of three middle fingers at arm’s length. The nebula shines faintly at magnitude 9.0, making it just visible through binoculars and an easy target for even small backyard telescopes.  

Demon Star.  On Halloween, Saturday, October 31, trick-or-treaters can hunt down a real stellar ghoul in the sky. That night, the naked-eye star Algol sits in the constellation Perseus, rising high in the northeastern evening sky. The star represents the eye of the monster Medusa from ancient Greek mythology, but what makes it so eerie is that it appears to wink at us.  

Algol, which means “ghoul’s head,” sits 93 light-years away and is actually two stars that orbit each other. From our vantage point here on Earth, the two stars are lined up so that one eclipses the other every 2.867 days, or 68 hours, 48 minutes, and 59.9 seconds. That makes Algol appear to fade and brighten

Known as an eclipsing binary variable, Algol is normally the second-brightest star in the constellation Perseus at 2.1 magnitude, which is about as bright as stars in the Big Dipper. But over a 10-hour period, Algol fades dramatically to 3.4 magnitude and then again brightens, as one star passes in front of the other. This week, Algol reaches its dimmest point at 8:50 a.m. ET on October 27 and 5:39 a.m. ET on October 30.

You can easily hunt down the demon star in the constellation Perseus, the hero, near the W-shaped constellation Cassiopeia and the bright star Capella of the constellation Auriga. Perseus looks somewhat like a lopsided K, with Algol located along one of the upper arms just a few degrees from the bright star Mirfak.

Mars and Venus. On Sunday, November 1, early risers get a chance to catch the goddess of love and the god of war team up in the low eastern sky just before dawn when super-bright Venus slides within 1 degree of Mars. The king of the gods, Jupiter, will be perched above, looking down on the pair.