Every 20 years, Jupiter and Saturn align in our night sky for an especially bright conjunction of the planets referred to as the "Christmas star."
They will be at their closest, and brightest, on Monday Dec. 21, the Winter Solstice.
But this year's alignment will be particularly special and rare, and not just because of the date on which it falls.
"It’s been nearly 400 years since the planets passed this close to each other in the sky, and nearly 800 years since the alignment of Saturn and Jupiter occurred at night, as it will for 2020, allowing nearly everyone around the world to witness this 'great conjunction,'” says NASA.
NASA says the planets will appear so close together that "a pinkie finger at arm’s length will easily cover both planets in the sky."
“Conjunctions like this could happen on any day of the year, depending on where the planets are in their orbits,” says Henry Throop, astronomer in the Planetary Science Division at NASA Headquarters in Washington, in a release. “The date of the conjunction is determined by the positions of Jupiter, Saturn, and the Earth in their paths around the Sun, while the date of the solstice is determined by the tilt of Earth’s axis. The solstice is the longest night of the year, so this rare coincidence will give people a great chance to go outside and see the solar system.”
The best chance to check out the "Christmas star" is about 45 minutes after sunset on Dec. 21 in the west/southwest sky. (The sun will set at 5:19 p.m. Dec. 21.)
And Great Parks of Hamilton County is promoting several locations in which to see this celestial spectacle — viewable in the night sky through Christmas Day.
And watch Cincinnati Observatory Astronomer Dean Regas discuss the alignment below: