(12/2021) The waning crescent moon is just above Mars in the dawn on December 2nd, and is new on December 4th. The waxing crescent moon is just below Venus in the dusk on December 6th. Compare their phases that evening in low power telescopes. The moon passes beneath Saturn on December 7th, and below Jupiter on December 8th. It is first quarter on December 10th.
The best meteor shower of the year, the Geminid meteor shower, peaks on the morning of December 14, with best observing after moonset about 3 AM. Look for a meteor a minute coming out of the NE. The full moon, the Yule or Long Night Moon, occurs on December 18th. The winter solstice, our shortest day, begins at 10:59 a.m.. The last quarter moon is on December 26th, and on News Eve, the waning crescent moon again returns to the right of Mars.
Prime time of planetary observing is fast ending. All three bright planets now in the west will soon vanish behind the Sun. This is most true of Venus, which overtakes earth this month and gets much larger in the telescope and even binoculars. The phase is 30% lit on December 1st, down to 15% by midmonth, down to 10% at Winter Solstice, and down to a mere 5% sliver by New Years. But she has grown to over an arc minute in size, the biggest any planet can appear from Earth. She will be low in the twilight then, and beside Mercury in dusk on December 30th about 40 minutes after sunset, a fitting ending to the year!
Saturn will be the next to vanish in the Sun’s glare, in January, and Jupiter by Valentine’s Day. As they are low in the SW, stay to low powers to see the 4 moons around Jupiter and Saturn’s rings while you can in the telescope.
The square of Pegasus dominates the western sky. South of it are the watery constellations of Pisces (the fish), Capricorn (Sea Goat), Aquarius (the Water Bearer), and Cetus (the Whale). Below Aquarius is Fomalhaut, the only first magnitude star of the southern fall sky. It is the mouth of Pisces Australius, the Southern Fish.
The constellation Cassiopeia makes a striking W in the NW. She contains many nice star clusters for binocular users in her outer arm of our Milky Way, extending to the NE now. Her daughter, Andromeda, starts with the NE corner star of Pegasus’’ Square, and goes NE with two more bright stars in a row. It is from the middle star, beta Andromeda, that we proceed about a quarter the way to the top star in the W of Cassiopeia, and look for a faint blur with the naked eye. M-31, the Andromeda Galaxy, is the most distant object visible with the naked eye, lying about 2.5 million light years distant.
Overhead is Andromeda’s hero, Perseus, rises. Perseus contains the famed eclipsing binary star Algol, where the Arabs imagined the eye of the gorgon Medusa would lie. It fades to a third its normal brightness for six out of every 70 hours, as a larger but cooler orange giant covers about 80% of the smaller but hotter and thus brighter companion as seen from Earth.
Look at Perseus’ feet for the famed Pleiades cluster; they lie about 400 light years distant, and over 250 stars are members of this fine group. East of the seven sisters is the V of stars marking the face of Taurus the Bull, with bright orange Aldebaran as his eye. The V of stars is the Hyades cluster, older than the blue Pleiades, but about half their distance. Their appearance in November in classical times was associated with the stormy season, when frail sailing ships stayed in port. Aldeberan is not a member of the Hyades, but about twice as close as the Hyades; distances in astronomy can be deceiving.
Yellow Capella, a giant star the same temperature and color as our much smaller Sun, dominates the overhead sky. It is part of the pentagon on stars making up Auriga, the Charioteer. Several nice binocular Messier open clusters are found in the winter milky way here. East of Auriga, the twins, Castor and Pollux highlight the Gemini. History buffs associate the pair with Jason and the Golden Fleece legend, for they were the first two Argonauts to sign up on his crew of adventurers.
South of Gemini, Orion is the most familiar winter constellation, dominating the eastern sky at dusk. The reddish supergiant Betelguese marks his eastern shoulder, while blue-white supergiant Rigel stands opposite on his west knee. Just south of the belt, hanging like a sword downward, is M-42, the Great Nebula of Orion, an outstanding binocular and telescopic stellar nursery. It is part of a huge spiral arm gas cloud, with active starbirth all over the place.
Last but certainly not least, in the east rise the hunter’s two faithful companions, Canis major and minor. Procyon is the bright star in the little dog, and rises minutes before Sirius, the brightest star in the sky. Sirius dominates the SE sky by 7 PM, and as it rises, the turbulent winter air causes it to sparkle with shafts of spectral fire. Beautiful as the twinkling appears to the naked eye, for astronomers this means the image is blurry; only in space can we truly see "clearly now". At 8 light years distance, Sirius is the closest star we can easily see with the naked eye. Below Sirius in binoculars is another fine open cluster, M-41, a fitting dessert for New Year’s sky feast.
