When Jupiter and Saturn appear as one
In the year 1226 A.D., the great Mongol Horde was swarming eastward from Central Asia, marauding its way into Bulgaria. Charles I, the future King of Naples, was born. Louis XIII — Louis the Lion — of France, died. So did St. Francis of Assisi.
And in the muddy-road March of that year, if anyone — peasant, tanner, monk or noble — looked into the night sky, they would have seen Jupiter and Saturn reel in so close together that on one night, they seemed one brilliant star.
Now, it will happen again. On the night of Dec. 21 — the night of the winter solstice, no less — Jupiter and Saturn will seem almost to touch in the southwest sky after sundown.
“It’s going to be spectacular,” said Diana Hannikainen, observing editor of Sky & Telescope Magazine
It’s the first time in nearly 800 years this greatest of Great Conjunctions will be visible. It’s our one and only chance to watch this dance.
“The next one will be in what…another 800 years?” said Geoff Chester, spokesman for the US Naval Observatory in Washington, D.C. “I’m not waiting around to see it.”
It will be wonderful for naked-eye astronomers and better yet for someone with a pair of binoculars. But if you have even a backyard telescope, you’ll be able to see Jupiter and Saturn together in the same fixed view with at least some of their many moons thrown in.
“Wouldn’t that be a picture?” said Monty Robson, director of the John. J. McCarthy Observatory in New Milford.
Bill Cloutier, one of the founders of the McCarthy Observatory, said he’ll have his telescope out.
“If the weather cooperates,” he said.
And if it doesn’t, there will be the nights leading up to the conjunction, as Jupiter and Saturn approach, and the nights that follow, as they take leave of each other. On the night of Dec. 16, there will be a thin crescent moon in the southwest sky, with the two planets nearby.
“It will be a pretty sight,” said Cliff Watley of Ridgefield, who helps lead the skywatching nights at the New Pond Farm nature center in Redding.
“I would tell everyone to
start watching now, even if it’s for only five minutes a night,” Hannikainen said.
The conjunction is occurring because everything in our solar system, and the universe, is moving.
The planets, including Earth, orbit the sun.
The farther out, the longer the orbit. It takes Jupiter nearly 12 Earth years to complete its circle around the sun. For Saturn, it is 29.5 Earth years.
And they’re also far away. Jupiter is 540.6 million miles away from Earth, Saturn, 993 million miles.
But they’re also the two biggest planets in our solar system. Jupiter is approximately 11 times the size of Earth and Saturn, nine times larger.
So we can see these two, which circle so far away, in the night sky.
Venus, Mars and sometimes Mercury are also
naked-eye objects. Sometimes, the circling orbits — including Earth’s — take them closer to the Earth and they appear brighter. Mars, for example, was close by and brilliant this October.
Every 20 years or so, the orbits of Jupiter and Saturn make them appear be to close together in our night sky, what’s called a Great Conjunction.
But this year, they’ll look like they’re close enough as to be nearly one on Dec. 21.
Chester of the Naval Observatory said such a conjunction may have occurred in 1623, but during daylight hours.
“This one, you’ll be able to see,” he said.
What’s best about this dance is that everyone who goes out on a clear night in a relatively dark place will be able to look up with a bit of wonder. You won’t have to travel long distance or wear special glasses or get out of a warm bed at 3 a.m. to see it.
“Kids won’t need anything,” Watley of Ridgefield said.
As for the conjunction happening on the night of the winter solstice, Chester said, it’s simply a matter of coincidence — the circling orbits of Earth, Jupiter and Saturn simply lined up for that night.
“There’s no cosmic significance,” he said.
But Hannikainen of Sky & Telescope said it’s nice to see all this wheeling going on while we swing from one season to the next.
“It makes it extra-special,” she said.
And one can imagine. “If you were a Wise Man and saw that, wouldn’t you follow it?” Watley said.