The Celestial Sphere

by Matthew Johnson

We begin the month of December with long nights reaching a maximum on the evening of the winter solstice, Dec. 21, with 14 hours and 55 minutes of darkness. After the 21st, the days begin to grow a few minutes longer each day, a time of year acknowledged throughout history by displays of lights and greenery celebrating the return of the sun.

The winter solstice occurs at 5:02 a.m. During the solstice, the South Pole of the Earth will be tilted to its greatest extent toward the sun, which will have reached its southernmost position in the sky. The sun is then below the equator directly over the Tropic of Capricorn at 23.44 degrees south latitude. The solstice marks the first day of winter (winter solstice) in the Northern Hemisphere and the first day of summer (summer solstice) in the Southern Hemisphere. During this time, the North Pole experiences 24 hours of darkness and the South Pole 24 hours of daylight.
Besides being the longest night of the year and marking the transition from fall to winter, the winter solstice of 2020 offers us a third and very special event—a great conjunction. A solstice with a great conjunction is a phenomenon that has been venerated since antiquity.

A conjunction is a lining up of celestial bodies where they become very close together. A great conjunction is the alignment of our two largest and brightest planets—Jupiter and Saturn. A great conjunction of Jupiter and Saturn occurs regularly (every 19.6 years, on average), but it is most often obscured by the sun or below the horizon to our view. However, this year’s great conjunction, being visible to the naked eye as well as occurring on the solstice, is an event that has not taken place for some 800 years. So, do not miss it! 

Jupiter and Saturn will appear to be so close together that they will look like a single bright double planet. It has been speculated that a great conjunction of Jupiter and Saturn inspired the Christmas story of the “bright star” that the wise men followed. Look to the West just after sunset for this impressive and rare planetary alignment on the eve of the winter solstice on Dec. 21. One can view Jupiter and Saturn approaching each other every night of December leading up the great conjunction on the 21st.

Other celestial events this month: 

Mars is located mid-heaven to the south and continues to be a bright glowing orange red as it recedes from the Earth, growing fainter each month.

 Dec. 13-14. The Geminids meteor shower is considered to be one of the best showers, producing up to 120 meteors per hour, many multicolored. The Geminids are produced by the Earth’s orbit entering a debris path left behind by asteroid 3200 Phaethon. The shower peaks after midnight on the nights of Dec. 13 and 14. A virtually new moon will ensure dark skies for what should be an excellent show this year. Meteors will mostly radiate from the constellation Gemini.

Additionally on Dec. 14 there is a total solar eclipse. However, the path of totality will only be visible in parts of southern Chile and southern Argentina, not in North America.

Dec. 21-22. The Ursids meteor shower is a minor meteor shower producing about five to 10 meteors per hour. It is produced by dust left behind by comet Tuttle. The shower runs annually from Dec. 17 to 25, peaking the night of the winter solstice continuing into the next morning. Best viewing will be just after midnight from a dark location far away from town lights. Meteors will radiate from the constellation Ursa Minor, the constellation containing Polaris, but can appear anywhere in the sky.
Phases of the Moon:

Dec. 8: Last quarter (left half of the moon illuminated).

Dec. 14: New moon (no visible moon). The best time of the month to observe faint objects such as distant galaxies and star clusters is during the few days before and after the new moon (when there is no moonlight to interfere).
Dec. 21: First quarter (right half of moon illuminated).

Dec. 30: Full moon. December’s full moon was known by Native Americans as the Cold Moon because this is the time of year when the winter air settles in and the nights become long and dark. This moon has also been called the Long Nights Moon, since it is close to the date of the winter solstice and is the moon before Yule.