Editor’s Note: We are looking up as HMNS Astronomer James Wooten explains the sky happenings for December before we jump into the new year.
Saturn is now well placed for observing in early evening. Face south-southwest at dusk to observe it.
Jupiter was opposite the Sun, and up precisely all night long, a month ago. This month, it is prominent in the east right at nightfall. No star at night is as bright.
Venus has entered the morning sky. Look for it in the east at dawn this month.
Mars is lost in the Sun’s glare and out of sight for the rest of 2023.
The Summer Triangle sets in the west. Watch for the Great Square of Pegasus almost overhead at dusk now and in the west by Christmas. Taurus, the Bull rises in the east, with Mars in his horns. Look for the Pleiades star cluster above reddish Aldebaran. Dazzling Orion, the Hunter rises shortly after dusk (by month’s end, it is already up at dusk). As Orion enters the evening sky, we transition from the relatively dim evening skies of autumn to the brilliant stars of winter. We are beginning to face away from the center of the galaxy, looking at stars behind us in our own part of our galaxy (the Orion Spur).
Moon Phases in December 2023
Last Quarter Dec. 4, 11:49 p.m.
New Dec. 12, 5:32 p.m.
1st Quarter Dec. 19, 1:39 p.m.
Full Dec. 26, 6:33 p.m.
At 9:28 pm on Thursday, December 21, the Sun is overhead as seen from the tropic of Capricorn, the farthest point south where this is possible. That’s because Earth’s North Pole is now tilted as far as possible away from the Sun. That’s why this is our winter solstice, the day when we have more night and less daylight than any other. Below the equator, this is the summer solstice because the South Pole is tilted towards the Sun as much as possible.
You will notice, however, that sunset on New Year’s Eve is up to ten minutes later than on December 1. Why, if the 31st is closer to the solstice? Although the shortest day (least daylight) occurs on December 21, the earliest sunset occurs for us about December 1. This is because the Sun’s apparent position in our sky varies like a sine wave; there is little difference in the Sun’s apparent height for about a month before and after the solstice. Due to Earth’s tilt, the Sun does indeed take a shorter, lower path across the sky on December 21 than on December 1, but only by about 1.5 degrees (your pinky at arm’s length blocks one degree). Meanwhile, Earth is slightly accelerating as it approaches perihelion just after the new year. This makes both sunrise and sunset happen a little later each night during December. Near the solstice, this small effect can dominate. Since most of us sleep through sunrise and watch sunset, days seem to lengthen from December 1-21 when they are in fact still getting shorter.
Our George Observatory is now open every Saturday night for observing! Purchase tickets in advance on our website.
Missed November’s sky happenings? See them here.