The solar system will give us an especially rare show to close out the year 2020: a Christmas star.
When you look into the sky on Dec. 21 – the winter solstice – Jupiter and Saturn will look like they're nearly touching, creating what's been dubbed the Christmas Star because this planetary event happens so close to Christmas.
This will be the first time they'll appear this close together since 1226, during the Middle Ages, Earth Sky reports.
“It’s the rare astronomical event where you can appreciate the motion of the planets around the sun without being some kind of astronomer,” Konstantin Batygin, professor of planetary science at the California Institute of Technology, told the New York Times.
“You can still go outside close to Christmas and say, ‘Wow, those two planets sure are close to one another, and they aren’t usually,'" Batygin added. "It’s one of these rare times when the majesty of the solar system presents itself to the naked eye."
The two plants will appear to be about a tenth of a degree apart or the thickness of a dime if you hold it at arm's length, NASA says.
Although Saturn and Jupiter will look super close from Earth – and they will be closer together along their orbital paths – they'll still be more than 400 million miles apart.
This will mark a once-in-a-lifetime spectacle for most adults – they won't appear this close together again until March 15, 2080.
How to see it
As soon as it gets dark on Dec. 21, go outside and look toward the southwestern portion of the sky. Grab a telescope or binoculars if you have them, but you should still be able to see the show with the naked eye anywhere on Earth, NASA says.
If the sky is clear, you should see two orbs shining steadily (not twinkling as stars do). Jupiter will shine much brighter and very low, while Saturn will appear golden. Saturn shines as bright as the brightest stars, but not as brightly as Jupiter, Earth Sky notes.
The New York Times says they'll look like a bright ball or a tipped-over snowman.
Earth Sky says Saturn will be just to the east of Jupiter, with NASA noting Saturn will appear as close to Jupiter as some of its moons.
This isn't just a one-night event. Deane Morrison of the University of Minnesota's Minnesota Institute for Astrophysics encourages people to follow the planets' approach and separation over several days, such as from Dec. 16 through Dec. 23. (Morrison points out that on Dec. 16, there will be a thin crescent moon that comes out below Saturn and Jupiter.)
NASA notes in the weeks leading up to Dec. 21 the two bright planets will visibly inch closer together with each passing day.
Why this is happening
This rare planetary event is called the great conjunction.
The term conjunction is used to describe the meetings of planets in our sky's dome, Earth Sky notes, and when it's the meeting of the solar system's two biggest planets (Jupiter and Saturn), it's called the great conjunction.
The great conjunction happens thanks to their orbital paths coming into alignment, as seen from Earth. Jupiter orbits the sun every 12-ish years, while Saturn's orbit around the sun takes nearly 30 years.
So, nearly every 20 years the two planets come into alignment to form the great conjunction.
Although the planets will align about every 20 years in this century (the most recent was in 2000), NASA calls this the "greatest" great conjunction between the two planets.
That's because it'll be the closest observable great conjunction of the two planets for almost 800 years.
“Alignments between these two planets are rather rare, occurring once every 20 years or so, but this conjunction is exceptionally rare because of how close the planets will appear to one another,” said Rice University astronomer Patrick Hartigan. “You’d have to go all the way back to just before dawn on March 4, 1226, to see a closer alignment between these objects visible in the night sky.”
"... It is fair to say that this conjunction is truly exceptional in that the planets get very close to one another. In the three thousand year interval from 0 CE to 3000 CE, only seven Jupiter/Saturn conjunctions were/will be closer than this one. Two of those (in 769 CE and 1623 CE) were too close to the Sun for Saturn to be seen without a telescope, and even Jupiter would have been difficult or impossible to detect from most locations with the naked eye for these events.
"If you are looking for a positive spin, the last time the two planets appeared this close to one another in the sky and were observable (i.e. not in the Sun's glare) was on the morning of March 4, 1226! That was back in the Middle Ages, when the Notre Dame Cathedral was first being built.
"For this conjunction, both planets will be visible in the same field of view in most small telescopes, along with some of Jupiter's and Saturn's moons. In fact, they will be so close it may be a challenge to separate them with the unaided eye for some people."
Geminids meteor shower this month, too
The year's best meteor shower – the Geminids – will peak overnight on Dec. 13 and the morning of Dec. 14 (Saturn and Jupiter will be inching closer together, too), NASA says.
This annual event will be active from Dec. 4-17, at which time the Earth will go through a trail of dusty debris left in orbit from asteroid 3200 Phaethon.
NASA says this year's meteor shower should be especially good because it coincides with a nearly new moon. This means the sky will be darker and the moonlight won't washout the fainter meteors, so more should be visible.
In the Northern Hemisphere, meteor activity is good all night, peaking around 2 a.m. To see them, get away from bright city lights and lie on the ground with your feet pointing south and look up at the sky.
The meteors can be seen anywhere in the sky but will appear to radiate from the constellation Gemini.