This December starts with a full moon in the sky and ends with another full moon. While the first full moon is officially on Nov. 30, for all practical purposes the night sky will be saturated with virtually full moonlight the first several days of December, pretty much killing serious stargazing. On Dec. 30, we’ll have an official full moon that many early Native American tribes referred to as the “Cold Moon,” which should come as no surprise.
Between these full moons there’s much going on in the nightly celestial theater. The biggest event is the historic conjunction between Jupiter and Saturn. A conjunction occurs when two or more astronomical bodies appear to be close together in the sky from our view on Earth. We see many of these throughout the year. The conjunction. though. between Jupiter and Saturn is monumental. The last time these two planets were this close together was when Galileo was still living!
Since this past summer, these two giant planets have been putting on a fantastic show. They’ve been faithfully side by side, with Jupiter being the brighter of the two. They’re getting even closer to each other in the night sky as they travel in their respective orbits around the sun. This month, they can be easily seen in the low southwestern sky toward the end of evening twilight, setting about an hour later. At the start of December, Jupiter and Saturn will be less than two degrees apart. That’s about the width of two of your fingers held together at arm’s length. Jupiter is to the lower right of Saturn. On Dec. 21, which coincidently is the Winter Solstice, Jupiter and Saturn will only be a tenth of a degree apart! This is the closest these planets have been to each other in the sky since 1623. They’ll be appearing as “double planet.” Consider the duo to be the “Christmas star” of 2020. After the year this world has had, we deserve a celestial treat like this! Just before the magnificent conjunction peaks, there will be a thin crescent moon close by the planets on Dec. 16 and 17 to really sweeten the sight!
Another marquee event this December is the annual Geminid meteor shower, one of the best of the year. This will be an excellent year for the Geminids because there will be no moonlight in the sky overnight. The Geminid meteor shower peaks on the night of Dec. 13-14. I’ll have much more on the Geminids next week in Skywatch.
Even without all of the special happenings this December, this is a great month for stargazing. Even though it’s generally much cooler (or colder), you get the longest nights of the year. In most locations. you can start your stargazing well before 6 p,m. Mars continues to fade after its big show in October, but it’s still the brightest star-like object in the southern evening sky. You might still be able to spot some of its surface features with a moderately sized telescope.
The great horse Pegasus is riding high in the south-southwestern sky not too far away from Mars. In the high northern heavens is Cassiopeia the Queen, resembling a big, bright, and nearly upside “W.” The Big Dipper is still very low in the north, but as December continues, you’ll notice that it begins evenings higher and higher in the northeast sky, standing diagonally on its handle. The Little Dipper is hanging by its handle above the Big Dipper, with Polaris, the North Star, poised at the end of the handle. Because Polaris is shining directly above the Earth’s North Pole, it appears as if all the stars in the sky in the northern hemisphere revolve around Polaris once every 24 hours, including our sun. You’re seeing the Earth’s rotation reflected in the sky.
Gazing to the east, just after evening twilight ends, you’ll be bombarded with all kinds of bright stars, and even more as you get later in the evening. You are witnessing the rise of the winter constellations, the best ones of the year in my opinion. Auriga the Chariot Driver and Taurus the Bull lead the charge. Above Taurus is the best star cluster in the sky, known as the Pleiades and the Seven Little Sisters. This is a young group of stars, over 400 light-years away that looks like a tiny Big Dipper. After 8 p.m., Orion the Hunter, the winter constellations’ grand centerpiece, climbs well above the eastern horizon. The three equally spaced stars in a row that make up the belt of the great hunter will definitely jump out at you.
Enjoy all that’s going on in nightly celestial theater this month. It’s more than worth bundling up for!
Mike Lynch is an amateur astronomer and retired broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and adventurepublications.net. Mike is available for private star parties. You can contact him at firstname.lastname@example.org.
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