Skywatch Line for Friday, December 6, through Sunday, December 8, 2019

This is Dudley Observatory’s Skywatch Line for Friday, December 6, through Sunday, December 8, written by Sam Salem.

On Friday, Sun rises at 7:12am and sets at 4:22pm; the waxing gibbous Moon rises at 1:46pm and sets at 1:14am. The Moon shines lower left of the Great Square of Pegasus on Friday night.

The date of earliest sunset depends on latitude, the farther north, the closer it occurs to the solstice. Earliest sunset of the year happens these days for our area (calculated at Schenectady latitude of 42.8 degrees N). The Sun sets at 4:22pm since December 2. It will set at 4:23 on December 16. This offset of the earliest sunset from solstice date (December 21) is balanced out by the opposite happening at sunrise. The Sun doesn’t come up its latest until January 2. The tilt of Earth’s axis and the eccentricity of Earth’s orbit cause this offset. For the southernmost U.S., around 30 degrees north latitude, the earliest sunsets of the year happen in late November. Closer to the Arctic and Antarctic Circles, the earliest sunset and earliest sunrise happen nearer the solstice.

Spot Mercury, at magnitude -0.6, low in the east-southeast as much as an hour before sunrise. Mercury is having its best dawn apparition of the year. Look for it very far below Arcturus. Mercury is closer to the lower left of fainter Mars and Spica. Mars, at magnitude +1.8 in constellation Virgo, is low in the east-southeast in early dawn. It sits to the upper right of Mercury. Brighter Spica shines farther upper right of Mars. This line of three expands farther each night as Mercury sinks lower and Mars and Spica get higher. Mars rises around 4:30am and Mercury rises few minutes after 5:30am.

Venus, at magnitude –3.9 in constellation Sagittarius, shines low in the southwest in evening twilight. It rises a little higher each week. Venus sets few minutes before 6:30pm. Jupiter, at magnitude –1.8, moves farther to the lower right of Venus in twilight. Jupiter sets almost an hour after sunset. It’s becoming difficult to spot before it sets. The gap between Venus and Jupiter increases from 6 degrees to 12 this week. Saturn, at magnitude +0.6 in constellation Sagittarius, is the steady yellow dot upper left of bright Venus. Every evening Venus gets about 1 degree closer to Saturn. The gap between them narrows from 13 degrees to 5 degrees this week. They’ll be just under 2 degrees apart on Tuesday and Wednesday next week. Saturn sets few minutes before 7pm.

Gerard Peter Kuiper was born on December 7 1905. The Dutch-born American astronomer discovered Miranda, a moon of Uranus, and Nereid, a moon of Neptune. The Kuiper Belt was named after his original suggestion of its existence outside the orbit of Neptune before it was confirmed as a belt of small bodies. Kuiper measured the diameter of Pluto. In 1947, Kuiper detected the existence of carbon dioxide and the absence of oxygen in the Martian atmosphere. In the 1960s, Kuiper served as chief scientist for the Ranger spacecraft crash-landing probes of the Moon. Ewen Whitaker, who worked under Kuiper, analyzed Ranger photographs and identified landing sites on the lunar surface most suitable for safe manned landings. Kuiper died in December 1973.

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