This is the Dudley Observatory Skywatch Line for Wednesday, December 30th and Thursday, December 31st written by Louis Suarato
Celebrate your year-end by seeking out the innermost planet, Mercury, about 40 minutes after sunset. Look approximately 5 degrees over the southwest horizon to catch Mercury before it sets around 5:40 p.m. below the constellation Capricornus. Mercury orbits the Sun once every 88 days, and rotates on its axis three times during two revolutions around the Sun. Of all the planets, Mercury’s orbital eccentricity is the greatest, as its distance at aphelion is 1.5 times farther from the Sun as it is at perihelion.
The bright stars comprising the asterism known as the Winter Circle, or Winter Hexigon, can be seen after 8 p.m. over the eastern horizon. The lowest star in the circle is also the brightest. That star is Sirius, in the constellation Canis Major. To the east of Sirius is Procyon, the brightest star in the constellation CanisMinor. Above Procyon is Pollux, in Gemini. Continuing clockwise, you’ll find Capella, in the constellation Auriga. Below, and south of Capella, is Taurus’ brightest star Aldebaran. Completing the circle is Rigel, in the constellation Orion.
The planetary procession continues when Jupiter rises at 10:40 p.m. just below the 68% illuminated, waning gibbous Moon. You may be able to see Jupiter in the daylight by using the Moon as a guide when it passes 1.5 degrees south of Jupiter at 1 p.m. EST on December 31st. Mars follows Jupiter about three hours later in Virgo. Another three hours later, Venus rises at the head of the scorpion, followed by Saturn an hour later. If you were successful in seeing Mercury, you’ll have an opportunity to see all the easily visible naked-eye planets.
The Big Dipper will be standing upright on its handle high over the eastern horizon during the pre-dawn hours. Follow the arc of the handle downward toward Arcturus. Use Arcturus to find Comet C/2013 US10 Catalina just 3 degrees to its right.