Conjunction Junction: Jupiter and Saturn Put on a Celestial Show
Social distancing? Not a thing in the night sky, where two giant planets make their closest observable approach to each other in 800 years.
Christmas is coming early for stargazers this year. On December 21 viewers in the West (and actually all over North America) will receive a rare gift: an ultra-close conjunction of the planets Jupiter and Saturn.
Readers will know that I’ve been geeking out over Jupiter and Saturn for months now. They’re two literal bright spots in a pretty bleak year. Watching the two planets promenade across the sky, moving a little closer to each other every night, reminds me that time is indeed passing, even if each day does sometimes feel like a featureless clone of the one before.
On the evening of December 21 the two planets will appear remarkably close to each other in the sky in an event astronomers are calling a “great conjunction.” How close will they appear? The two will occupy a piece of the sky considerably smaller than the size of the full moon. If you hold your hand out at arm’s length that evening and raise it to the sky, you will probably be able to blot out both planets with your pinky. They may even appear as one point of light to the naked eye.
Good, Sure, but Great?
So what’s so great about this conjunction? Well, for starters, it’s incredibly rare that two bright planets appear so close together in the sky. These two haven’t gotten this cozy since the 17th century—and no one got a very good look at that event because the planets were too close to the sun then. You’d have to go back to 1226 to find another time when Jupiter and Saturn appeared this close and anyone could see it.
Another remarkable aspect of this week’s event is that it involves two bright objects. Jupiter is the third-brightest thing in the night sky (after the moon and Venus). Saturn isn’t quite that bright, but it’s still easily visible to the naked eye, even in cities. Finally, the conjunction is also visible in the early evening. This isn’t something you’ll have to set an alarm for. The two planets are fairly high in the sky at sunset.
Catch the Conjunction
The best time for viewing the conjunction should be about an hour after sunset. That’s when it’s dark enough for the planets to really shine, and although they are setting, they won’t be too close to the horizon yet. Look to the southwest, toward where the sun just set. Jupiter and Saturn will be about one third of the way between horizon and zenith. An astronomy app can help if you’re really lost, but shouldn’t be necessary. (I like SkyView, which is available for both iOS and Android.)
If you have binoculars, try looking at the two planets with them. Jupiter will be a pale orange disk, and you should be able to see four points of light flanking it—those are Jovian moons. Saturn will be slightly yellowish, and may seem slightly oblong—that’s because of its rings. If you have a small telescope, dust it off. With even a small one, you can see dark orange bands on the surface of Jupiter, and those striking rings of Saturn will be clearly separated from the body of the planet.
If you miss Monday’s show, never fear. The planets will remain unusually close to each other for several more weeks. Don’t dawdle too much, though, because these two orbs won’t have a conjunction this great again until 2080. Best to try to make time this holiday season to catch nature’s own light display.