Skywatch Line for Friday, December 8 through Sunday, December 10, 2017

This is Dudley Observatory’s Skywatch Line for Friday, December 8 through Sunday, December 10, written by Sam Salem.

On Friday, Sun rises at 7:14am and sets at 4:22pm; Waning Gibbous Moon reaches transit altitude of 61 degrees south at 4:25am, sets at 11:31am, and rises at 10:19pm. Last quarter Moon occurs on Sunday at 2:51am.

The 0.5-magnitude Saturn is sinking ever lower as it descends toward a December 21 conjunction with the Sun. Mars, at magnitude 1.7, is the first planet to rise in the early morning hours. It appears shortly before 4am. The red planet resides in Virgo, about 5.5 degrees east of first-magnitude Spica. Jupiter, at magnitude -1.7, rises an hour later. It climbs to an altitude of 20 degrees half an hour before sunrise. The magnitude –3.9 Venus clears the east-southeast horizon at that time. Venus’s current apparition is finally drawing to a close. The “morning star” will become more difficult to catch each passing week.
On Friday night, look eastward to catch the Moon and the star Regulus ascending over the horizon. Wake up before dawn to see the celestial couple. Look first for the waning gibbous Moon. The nearby bright star will be Regulus, the brightest star in Leo the Lion. Regulus is sometimes called the Heart of the Lion. Find the famous constellations Orion the Hunter, and see the Milky Way running behind it. To see the Milky Way, you’ll need a dark sky. Throughout December, the constellation Orion is up by mid-evening. Orion rises earlier each evening, and, by late December, Orion is seen at nightfall or early evening. Look on either side of the Belt stars for two very bright stars. One is the reddish star Betelgeuse. The other is bright, blue-white Rigel. Given a dark sky, you can see this archway of stars running near Betelgeuse on the sky’s dome. When you look at this band of luminescence, the combined glow of billions of stars, you’re viewing the galactic disk edgewise. In the month of August, the Milky Way appears broad and bright during the evening hours. At that time of year you are gazing toward the center of the galaxy. If you see the Milky Way near the constellation Orion this month, it would look faint in contrast to the August Milky Way. That’s because in December you’re looking toward the galaxy’s outer edge, where there are fewer stars between Earth and intergalactic space.
Find the constellation Auriga the Charioteer with its brilliant yellow star Capella in the northeast at early evening. The pentagon-shaped pattern hits the zenith, or the highest point in the sky, around midnight and finishes up in the northwest at dawn. The constellations Auriga and Orion always climb highest for the night in concert. Auriga shines above to the north of Orion the Giant Hunter. There are several easy-to-find and famous star clusters in Auriga. With binoculars, you might be able to spot M36, M37, and M38. To the south of these star clusters, also close to the galactic equator, look for M35 in the constellation Gemini the Twins, at the foot of Castor. Auriga’s stars Menkalinan and Theta Aurigae run north to south. They point northward to Polaris, the North Star, and south to Orion’s bright ruddy star Betelgeuse. With binoculars, check out the star cluster M35 between Theta Aurigae and Betelgeuse.

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