This is Dudley Observatory’s Skywatch Line for Friday, December 25, through Sunday, December 27, written by Sam Salem.
On Friday, Sun rises at 7:25am and sets at 4:27pm; Moon sets at 2:58am and rises at 1:41pm. On Friday, the pole-to-pole terminator that divides the lit and dark hemispheres of the waxing gibbous Moon will fall to the left of Sinus Iridum, the Bay of Rainbows. The circular 155-mile diameter feature is a large impact crater that was flooded by the same basalts that filled the much larger Mare Imbrium to its right forming a rounded, handle-shape on the western edge of that mare. You can see it easily in binoculars and backyard telescopes.
On Saturday and Sunday nights, the waxing gibbous Moon shines in front of the constellation Taurus the Bull. Despite the lunar glare, you might see this constellation’s two major signposts, the star Aldebaran and the Pleiades star cluster, or the Seven Sisters. Aldebaran marks the tip of a V-shaped pattern of stars, a star cluster called the Hyades, representing the Bull’s face. Aldebaran isn’t part of this star cluster. It’s a chance alignment, with the Hyades cluster at more than twice Aldebaran’s distance away. Ruddy Aldebaran depicts the Bull’s red eye.
On Friday, as Jupiter and Saturn move apart, they’re sinking quite low in the southwest in twilight. Jupiter and Saturn separation widens to 0.5 degrees on Friday. They’ll fit together in telescopes’ low-power view. Don’t expect to see much of any telescopic detail on the two planets due to the poor atmospheric seeing at their low altitude. Mars, about magnitude –0.5 in constellation Pisces, shines bright yellow-orange very high in the south during early evening.
On Friday, lookout for a flying sleigh, one reindeer in the sky, Rangifer. This is one of the old star constellations. Today, astronomers recognize 88 constellations outlined by the International Astronomical Union. Before this ruling, the way constellations were drawn and named wasn’t regulated. Therefore, many constellations have come and gone. Rangifer is one of these extinct constellations. This reindeer-shaped pattern of stars was created by 18th-century French astronomer Pierre Charles Le Monnier. The constellation has also been called by the name Tarandus. Both words mean “reindeer” in Latin. You can find them in the region between Polaris and Cassiopeia, where Camelopardalis and Cepheus reside. You may need a dark location with no clouds to be able to locate these faint constellations.
Friday marks the 378th. birthday of Sir Isaac Newton. The English physicist and mathematician, widely recognized as one of the most influential scientists of all time and a key figure in the scientific revolution, laid the foundations for classical mechanics. Additionally, Newton made seminal contributions to optics, and he shares credit with Leibniz for the development of calculus. He built the first practical reflecting telescope. The statement of his three laws of motion is fundamental in the study of mechanics. Newton was the first to describe the Moon as falling in a circle around the earth under the same influence of gravity as a falling apple, embodied in his law of universal gravitation.