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The Sky This Week, 2016 December 6 - 13

The Moon Before Yule and an observatory's birthday.
MoonVenusMars_161202_01small.jpg
The Moon, Venus, & Mars, 2016 December 2,
imaged from the dome of the 12-inch telescope, USNO, Washington, DC

The Moon brightens the evening sky this week, waxing toward the Full phase as she courses through the late autumn and early winter constellations. Full Moon occurs on the 13th at 7:06 pm Eastern Standard Time. December’s Full Moon is known as the Moon Before Yule in the skylore of European Christianity. Other names, such as the Cold Moon, Big Moon, and Long Night Moon, reflect the influence of Celtic and Native American lore. December’s Full Moon occurs near Luna’s most northerly declination for the year, flooding the winter landscape with her pale light. This year she appears a bit brighter than usual thanks to the Full phase occurring near the Moon’s close perigee, which falls on the 12th. On the evening of the 12th you’ll find the nearly-full Moon pass through the heart of the Hyades star cluster which forms the "face" of Tauris, the Bull. Watch Luna creep closer to the bright star Aldebaran as the evening passes. At 11:07 pm EST the star will wink out as the Moon’s limb covers it. You can see it re-appear at 12:21 am.

The Full Moon washes out the annual Geminid meteor shower, which peaks on the night of the 13th. This is normally one of the year’s most reliable showers, and under dark skies it usually produces one or two "shooting stars" per minute. The meteors are generally slower than the August Perseids, and the radiant, in the constellation of Gemini, is well-placed after around 10:00 pm. Bright moonlight will hamper the number of meteors that the average observer will see this year, but a patient observer may be able to spot 20 or so per hour, even from urban locations.

The 6th is a special day for us here at the U.S. Naval Observatory. It was 186 years ago on that date that Navy LT Louis M. Goldsborough received orders from the Secretary of the Navy to establish a "depot" for the proper care, repair, and rating of the Navy’s navigational instruments. With a budget of only $330, Goldsborough established a small astronomical observatory at 17th and G Streets, NW in which he set up a small transit instrument to determine time to calibrate marine chronometers. Chronometer rating became a core function of the USNO for the next 120 years. Since Goldsborough’s time the Observatory has moved four times within the District of Columbia, culminating in the move to our present site in 1893. Today, with a staff of about 120 people at our DC location, the U.S. Naval Observatory is the world’s leading authority on spatial and temporal reference frames, providing precise astrometric and timing data to the Department of Defense and to astronomers across the globe.

Venus continues to climb into the early evening sky as she begins her northward trek through the stars of Capricornus. You should have no trouble finding her just after sunset, and sharp-eyed observers would probably be able to find her well before the Sun goes down. She will continue to dazzle early-evening skywatchers until the coming spring.

Mars continues to move eastward against the faint stars of Capricornus. On the evening of the 10th he passes just over a degree north of the second-magnitude star Deneb Algedi, the brightest star in the constellation.

Jupiter rises at around 2:00 am and is high in the eastern sky as morning twilight gathers. He is slowly drifting eastward toward the bright star Spica in the constellation of Virgo. He will cozy up to the star in late January.

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