Stars over Sisters 12/27/2021
Last updated 12/8/2021 at Noon
During late fall and early winter, observers in the northern hemisphere have an opportunity to see the 24th largest constellation by area: Perseus the Hero. To locate it, draw an imaginary line from the circumpolar constellation of Cassiopeia (the “W”) to the zodiacal stellar grouping known as Taurus. Except for the two end points, the entire length of this line resides within Perseus. Look for it overhead during the evening hours this month.
Perseus contains eight stars with proper names, the brightest of which is Mirfak with a visual magnitude of 1.8. Classified as a supergiant, it resides in the middle of a cluster of stars called the Alpha Persei Cluster, which is a fine sight in binoculars. Mirfak is 510 light-years away.
Perseus’ second brightest luminary is Algol, the famous variable star that changes brightness over time. The reason for this is that the two stars in this binary system eclipse each other (from our line of sight) every 2.87 days.
This constellation contains its fair share of deep- sky objects, two of which were cataloged by Charles Messier. Located about five degrees northwest of Algol is M34, a modestly bright cluster of about 80 stars.
Planetary nebula M76, aka the Little Dumbbell Nebula, is positioned along Perseus’ extreme western border. As is the case for all planetary nebulae, M76 consists of a dim gaseous shell that was expelled from a medium-to-low mass star nearing the end of its life. Because it is so faint, this object is generally regarded as the hardest of the Messier objects to observe. It is located about 2,500 light-years from the earth.
Perseus was a figure in Greek mythology who was legendary for dispatching many monsters. His more notable feats include the slaying of Medusa and the rescue of Andromeda. He was born in ancient Greece to the god Zeus and a mortal woman named Danae. When Perseus grew up, King Polydektes sent him to kill the Gorgon Medusa to free his mother, a nearly impossible task, which he managed to complete.
On his journey back to Greece, he rescued the Ethiopian princess Andromeda from Cetus the Sea Monster, to whom she was being sacrificed. He achieved this feat by showing Cetus the horrible, severed head of Medusa, which immediately turned the beast to stone. Afterward, Perseus and Andromeda were married and eventually placed next to each other in the sky.
The winter solstice arrives at 7:59 a.m. PST on December 21, signaling the start of the winter season in the northern hemisphere. On this day, the sun will reach its annual southernmost latitude, resulting in the shortest period of daylight of the year.
The brightest comet of the year is now in the inner solar system and may become visible to the unaided eye this month. Greg Leonard discovered it on January 3, 2021, from the Mount Lemmon Observatory in Arizona. The comet will pass closest to the earth on December 12, at a distance of 21.7 million miles, and be nearest the sun on January 3, 2022.
The best opportunity to view the comet will be a four- or five-day window beginning on December 14, though light from a waxing gibbous moon will be an interfering annoyance. Using binoculars, look for it below and to the right of Venus low in the southwest about an hour after sunset. With each successive day, the comet will move to the left (southward) along the horizon.
The three most noticeable planets this month, Venus, Saturn, and Jupiter, will appear at dusk in the evening sky. Venus reached its greatest brilliance on December 4. Near the end of the month Mercury will join the party, leaving Mars as the only naked-eye planet visible in the morning sky.
The first and last parts of the month will feature dark skies, but from new moon on December 3 to the Full Cold Moon on December 18, night will gradually brighten. After the last quarter moon on December 26, darkness will return to the evening sky.
Here’s December’s dark- sky preservation tip: Use warmer 2700 Kelvin lights instead of harsher white and cooler blue ones. Make sure to turn off Christmas lights at night. Doing so will save energy and lower light pollution levels. Using warmer lights has additional benefits, such as helping to induce more restful sleep.