The Summer Triangle takes a bow as it prepares to exit the evening sky for another year. It’s well up in the west as night falls, with Vega, its brightest member, forming the lower right point. It drops from view before midnight. In the meantime, Gemini climbs higher into the evening sky. Look for its “twins,” the stars Pollux and Castor, low in the east at nightfall, with the rest of the constellation spreading above and to the right. The planets Venus and Mars move toward each other this month, with orange Mars to the upper left of Venus, the Evening Star. They’ll pass each other in early 2017.
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In the Sky This Month
December 4: Moon and Mars
The Moon slides past the planet Mars tonight. Mars looks like a bright orange star close to the left of the Moon. The planet Venus, the brilliant “evening star,” stands well to their lower right in early evening.
December 5: Guiding Lights
Three planets line up to the lower right of the Moon tonight. Mars is closest to the Moon, with Venus, the “evening star,” farther along the same line. Mercury is farther still, just above the horizon, and visible mainly from the southern U.S.
December 6: Guiding Lights II
The Moon reaches first-quarter tonight, signifying that it is one quarter of the way through its month-long cycle of phases. The cycle reaches its zenith at full Moon on the night of December 13.
December 7: Sculptor
The faint constellation Sculptor, the sculptor’s workshop, passes across the south and southwest on December evenings. It was one of 14 constellations created in the 1750s by French astronomer Nicolas Louis de la Caille.
December 8: Fire and Water
The ancient elements of fire and water sit side by side low in the southern sky at this time of year. Fire is represented by the constellation Fornax, the furnace. To its east is the watery constellation Eridanus, the river.
December 9: Vega
Vega, one of the night sky’s brightest stars, is disappearing from evening view this month. Tonight, it sets around 9:30 or 10 p.m., but by month’s end it will set by about 8:30. Look for it in early evening, low in the northwest.
December 10: Capella
Capella, one of the brightest stars in the night sky, is in the northeast at nightfall and soars high overhead later on. What we see as Capella is really two stars. Each star is bigger, brighter, and heavier than the Sun.