Maybe you’ve already noticed them. You’ve certainly heard the hype.
Look southwest around the end of twilight. There you’ll see two bright “stars,” one brighter than the other. They’re the planets Jupiter and Saturn. Jupiter is the brighter one: Saturn is just to its upper left.
They’ve been in the evening sky since last summer, but now they’re creeping closer together from Earth’s moving point of view. On December 21st they’ll pass by each other super-close. In fact, this will be their closest conjunction easily visible since the year 1226.
Excitement is building. You may have read that they will “light up the sky.” That they will form the “first double planet” in centuries. Even that they will form “a new Christmas Star” of the same kind as the old one.
Horse patooties. That’s the work of headline writers who live by clicks and gullibles repeating it. The real doings in the sky are cool enough! Here’s your guide for what to watch.
The conjunction
Jupiter and Saturn are already close to each other. Go look southwest around the end of dusk. Watch them narrow the gap night by night.
When they pass each other on December 21st they’ll appear a mere tenth of a degree apart – about the width of a toothpick held at arm’s length! If you have good distance vision they’ll look like a tight double star, very unequal in brightness. With mediocre distance vision, they’ll blend into one. But since Saturn is less than a tenth as bright as Jupiter, the combination of the two will be only the slightest trace brighter than Jupiter alone. In fact, Jupiter by itself shone brighter all summer (when we were closer to it) than the combined pair does now.
Bring binoculars or a telescope if you have them. The two planets will fit in a telescope’s view together, definitely an unusual sight. Just don’t expect to see Jupiter’s cloud belts or much of Saturn’s rings. When you’re looking that low in the sky you’re looking through thick layers of air, which blur the telescopic view.
December 21st is also the date of the solstice (at 5:02 a.m.), the start of winter. But that’s just a coincidence.
More Astro-sights
There are more dates to put on your calendar! The thin crescent Moon hangs below Jupiter and Saturn on the evening of December 16th, then to the upper left of them on December 17th. By then the planets have closed to about a pencil width at arm’s length. Think photo opportunity! Use a long lens or maximum zoom, with your camera on a tripod or otherwise solidly braced. Get some nice scenery in the late-twilight foreground.
Meanwhile, late on the night of December 13th the annual Geminid meteor shower should be at its most active. Best times to watch are between about 10 pm and the first light of dawn on the 14th. Layer up super-warm, and bring a reclining lawn chair to a dark spot with an open view of the sky overhead and no nearby lights to get in your eyes. Lie back and gaze up into the stars. Be patient. As your eyes adapt to the dark, you may see a meteor every minute or two on average even through the light pollution over Bedford.
It’s a big universe out there.
Oh yes, about those horse patooties. The sky will not light up when the planets reach conjunction. Nor are close conjunctions all that rare; you may remember the even brighter, more spectacular double-planet pairings of Venus and Jupiter that were visible from Bedford and around the world in June 2015 and February 1999. Nor will this month’s planet pair roam the Earth to hang over a particular stable in a particular town. In fact, despite centuries of guesses that one conjunction or another might have been behind the story of the Christmas Star, there’s not the slightest indication that it involved anything physical or astronomical.
Alan MacRobert, a Bedford resident since 1988, is a semi-retired senior editor of Sky & Telescope magazine in Cambridge, “the best astronomy magazine in our half of the Earth” he informs us.
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Extremely informative!