This is Dudley Observatory’s Skywatch Line for Friday, December 20, through Sunday, December 22, written by Sam Salem.
On Friday, Sun rises at 7:22am and sets at 4:24pm; the waning crescent Moon rises at 12:53am and sets at 1:07pm.
Winter solstice occurs at 11:19pm on Saturday. At that moment, the Sun reaches its farthest point south in the sky. The solstice marks the official beginning of winter in the Northern Hemisphere. Saturday night has more hours of darkness than any other night of the year. However, for our area, the earliest sunset occurred about two weeks ago and the latest sunrise won’t happen until early January.
Mars grows more prominent before dawn with each passing week. The Red Planet now rises by 4:30am and climbs 20 degrees above the southeastern horizon, an hour before sunrise. Mars glows at magnitude 1.6, in constellation Libra the Scales. The waning crescent Moon stands 9 degrees above Mars on Sunday morning.
The Ursid meteor shower peaks on Sunday night. The shower’s radiant, or the point from which the meteors appear to originate, lies in constellation Ursa Minor near the bowl of the Little Dipper. The radiant is visible in the north all night, but it climbs higher as dawn approaches. The waning crescent Moon won’t interfere much even after it rises. Observers with clear skies typically see 5 to 10 Ursid meteors per hour at the peak. This year, astronomers predict this number could briefly double or triple from the normal rate.
The Summer Triangle of bright stars remains prominent during the early evening. Approximately one-third of the way to the zenith lies the Triangle’s brightest member, magnitude 0.0 Vega, in the constellation Lyra. Nearly 25 degrees above Vega lies magnitude 1.3 Deneb in Cygnus. And 35 degrees to Vega’s left lies magnitude 0.8 Altair in Aquila. Altair sets around 9:30pm.
Try to spot Neptune through binoculars this weekend. The distant planet lies halfway to the zenith in the south-southwest near the end of evening twilight and doesn’t set until nearly 11pm. The magnitude 7.9 planet appears against the backdrop of constellation Aquarius, almost 2 degrees west-southwest of the 4th-magnitude star Phi (φ) Aquarii. You’ll need a telescope to see Neptune’s blue-gray disk.
Around 8pm this weekend, find an open view right down to the east-southeast horizon and watch for Sirius to come up about two fists at arm’s length below Orion’s vertical Belt. When a star is very low, it tends to twinkle quite slowly in vivid colors. Shimmering and color changes happen when a bright star as Sirius shines through the Earth’s atmosphere. The varying density and temperature of Earth’s air affect star light, especially when the star is low in the sky. Sirius is bright enough to show these effects well, especially with binoculars.