Skywatch Line for Wednesday and Thursday, December 20 and 21, 2023
This is Dudley Observatory’s Skywatch Line for Wednesday and Thursday, December 20 and 21, written by Alan French.
The Sun rises at 7:22 A.M. on Wednesday and sets at 4:24 P.M. On Thursday it rises at 7:23 and sets at 4:24. This Thursday has 2 minutes less daylight than last Thursday.
In the northern hemisphere, the Winter Solstice, at 10:27 P.M. EST on Thursday, December 21, marks the official start of winter. The Sun will begin its journey back north and our days will start growing longer.
The Moon reached first quarter on Tuesday and is now headed toward full. On Wednesday night the Moon will be toward the south southeast as darkness falls. At 7:00P.M. it will be just past due south and its visible face 63 ½ percent sunlit. Thursday night at 7:00 it will be toward the south, 74% sunlit, and bright Jupiter will be 7 ½ degrees to the Moon’s left.
Jupiter is now due south and highest at 8:10 P.M. Around its highest is the best time to observe the giant gas giant with a telescope. At Jupiter’s altitude of 59 degrees the telescope is looking through less atmosphere and the view is likely to be steadier. We generally do not get good views of the planets when they are low in the sky. The ecliptic, the apparent path of the planets among the stars, is higher from the northern hemisphere in the winter.
Venus continues to slowly move lower in the morning sky, but is still bright and prominent in the southeast before dawn. On Wednesday morning it will be just under 19 degrees above the southeastern horizon at 6:30. On Thursday morning at 6:30 it will be just under 18 ½ degrees high. By January 1 it will be 17 degrees high at 6:30 A.M.
If you are up early Thursday morning there is a bright and interesting pass of the ISS (International Space Station). We see satellites because they are up in sunlight while we are down in the Earth’s shadow and darkness. Sometimes a satellite will move into or out of the Earth’s shadow while high in the sky, vanishing or appearing when well above the horizon. On Thursday the ISS will move out of the Earth’s shadow and into view when high above the horizon.
The ISS will first appear 53 degrees above the northern horizon at 5:32:19 A.M. (HH:MM:SS). Its appearance will be just over one-third of the way from Polaris, the North Star, to the star at the top front of the bowl (Dubhe). You will see that the bowl is hanging downward, so Dubhe is the lowest star in the bowl. Soon after emerging from the Earth’s shadow the ISS, moving down to the northeast, will shine at a brilliant magnitude -3.5, making it easy to spot.
After moving into view, the ISS will be moving toward the back of the Little Dipper’s bowl. It will begin crossing through the Little Dipper beginning at 5:32:34. The ISS will pass just north of bright Vega, 16 degrees above the northeastern horizon, just before 5:35 A.M. and then fade from view low in the sky as it approaches the horizon.