Stars over Sisters 11/30/2022

Perseus is a constellation in the northern hemisphere that is most visible in the late summer and autumn months. By mid-December, it lies overhead at 9 p.m. local time.

In Greek mythology, Perseus the Hero was the son of Zeus and a mortal woman named Danaë. King Polydectes tasked Perseus to kill the Gorgon Medusa, whose gaze was so horrible it turned men into stone. He was able to defeat her by looking at her reflection on his shield and beheading her, causing the mythical winged horse Pegasus to be born.

On his voyage home after slaying Medusa, he rescued Queen Cassiopeia’s daughter Andromeda from Cetus the sea monster. Those three characters also happen to be constellations, two of which border Perseus in the night sky.

The brightest star in Perseus is Mirfak (Alpha Persei), which shines at a magnitude of 1.8. It is a supergiant star that is more than 100 times larger and has a luminosity that is 5,400 times greater than our sun. Yet it’s the constellation’s second brightest star, Algol, that garners all the fame.

Algol (a.k.a. the Demon Star) is a variable star that dims and brightens with clockwork regularity, completing one cycle in two days, 20 hours, and 49 minutes. The phenomenon is caused by two stars very close together that rapidly orbit each other. When the larger but dimmer star moves in front of the brighter one, Algol’s magnitude drops from 2.1 to 3.4. No optical aid is necessary to see Algol fade and brighten—just look up. There is a third member of the Algol star system, but it is considerably dimmer and orbits the two eclipsing stars at a much greater distance.

Because the winter branch of the Milky Way runs through the constellation, there is a good assortment of deep-sky objects here. One of the most interesting of these is planetary nebula M76, also known as the “Little Dumbbell,” or “Cork Nebula.” It was formed when a sun-like star exhausted its nuclear fuel, causing a shell of gas from its outer atmosphere to be expelled into nearby space. The object is located approximately 2,500 light-years away.

Each year one of the most prolific displays of shooting stars occurs in December. The Geminid meteor shower is expected to peak on the night of December 13 into the early morning hours of December 14, when about 120 meteors per hour will fill the skies. This year, however, light from a waning gibbous moon will mask all but the brighter meteors.

Winter in the Northern Hemisphere begins at 1:48 p.m. PST on Wednesday, December 21. At that time the sun will reach its southernmost point on the ecliptic and appear directly overhead somewhere on the Tropic of Capricorn, at a latitude of 23.5 degrees south. Called the winter solstice, this event results in the shortest amount of daylight in a 24-hour period.

All five naked-eye planets will be spread across the evening sky in December. Mercury and Venus will appear low in the southwest, still in twilight after sunset. After mid-month, the two inferior planets will be easier to find. Saturn is in the same part of the sky, too, only several degrees higher and a bit farther east. Brilliant Jupiter lies even farther to the east in the constellation of Pisces.

But the “star” of the evening parade is Mars, which reaches opposition on December 8. Though not quite as luminous as Jupiter, the fourth planet from the sun, currently located in Taurus, will glow brightly with a reddish hue. Take time to compare this color with the nearby first magnitude star Aldebaran.

This month’s dark-sky tip is to make your outdoor lighting targeted. Use fully shielded lamps that direct light only on areas you wish to be lit. In this way, you can illuminate the area you intend to light without drawing your eye to the light source.

With the holidays coming up, please be mindful of the length of time you use decorative lighting. Consider turning these lights off after 10 p.m.