Skywatch Line for Wednesday and Thursday, December 27 and 28, 2023

This is Dudley Observatory’s Skywatch Line for Wednesday and Thursday, December 27 and 28, written by Alan French.

The Sun rises at 7:25 A.M. on Wednesday and sets at 4:28 P.M. On Thursday it rises at 7:25 and sets at 4:28. Now that we are past the Winter Solstice, and the Sun has started its journey back north, the days are lengthening again. This Thursday has 1 ½ minutes more daylight than last Thursday.

The Moon was full early Tuesday evening and is now moving toward third quarter. The next two nights will be dominated by a bright, almost full, gibbose Moon. On Wednesday the Moon, just under 99% sunlit, will rise at 4:50 P.M. in the northeast. The Moon is in the constellation Gemini, the Twins, and on Wednesday night not far from Castor and Pollux, the two brightest stars in the constellation, and the names of the twins. By 6:00 P.M. the Moon will be almost 10 degrees above the east northeastern
horizon and just under 6 ½ degrees away from Pollux. During the night you can see the Moon’s motion among the stars by watching it slowly move closer to Pollux.

Your hand, held at arm’s length, is a useful tool for measuring angular distances in the sky. Your first three fingers, held close together at arm’s length, span 5 degrees. Your pinky spans just 1 degree. By 8:00 P.M. Pollux will be just over 5 degrees from the lunar limb. By 10:00 P.M., Pollux will be just over 4 degrees away. The Moon will be due south, 74 degrees above the horizon, just after 1:00 A.M. Thursday morning, and Pollux will be just over 3 degrees away. At 5:00 A.M., with the Moon high in the west, just over 2 degrees will separate it from Pollux.

On Thursday night the Moon rises at 5:55 P.M. a little north of northeast. Its visible face will still be 96% in sunlight. By 8:00 P.M. it will be 29 degrees high. Note how much its position has changed since 8:00 P.M. Wednesday. It is no longer in Gemini, but is now in Cancer, the Crab.

Jupiter continues to dominate the evening sky. The largest gas giant in our solar system is now due south and highest at 7:42, when it will be 59 degrees above the horizon. The hour around its highest point in the sky is the best time to observe Jupiter through a telescope.

Brilliant Venus still dominates the morning sky. It rises in the east southeast at 4:21 A.M. and is 15 degrees above the southeastern horizon by 6:00 A.M. By 7:00 P.M. our inner neighbor will be 22 degrees high and
morning twilight obvious.