Saturn and Jupiter come close to each other about every 20 years, but rarely as close as they will Monday evening.
Jupiter and Saturn look like bright stars and are easily visible to the naked eye with a clear sky at night. On December 21, beginning around 5 p.m. EST, the two planets will barely be distinguishable from one another because of how close they will be.
This is the closest the two planets have been nearly 800 years - since March 4, 1226.
Steve Fentress, director of the Rochester Museum & Science Center's Strasenburgh Planetarium, said you can look to the southwestern sky just after sunset. Be sure to look low.
“Saturn is about 450 million miles beyond Jupiter, they’re just along the same line of sight,” Fentress said. “Jupiter passes Saturn in the sky about every 20 years, but rarely is it this close. So it’s a lucky alignment, and a fun thing to see. I hope we get a break in the clouds."
If you miss the alignment Monday night, you can still see the two planets fairly close together over the next couple nights.