Jupiter and Saturn, the two largest planets in the Solar System, will be stationed in nearly the same spot in the night sky on Monday, creating a bright spectacle.
The positions of the two planets align once every 20 years, according to NASA. While conjunctions happen several times during the course of a typical lifetime, a conjunction of this magnitude is quite rare. The last time the two planets were this close to each other in the night sky was 400 years ago, but no one was able to see it as that conjunction occurred during the day.
The last time a conjunction of his magnitude happened at night was 800 years ago.
The best time to view the conjunction will be 5:30 p.m. to 7:00 p.m. in the southwest sky. Jupiter will appear to be brighter than Saturn as it is closer and larger.
So what causes the conjunction?
“You can imagine the solar system to be a racetrack, with each of the planets as a runner in their own lane and the Earth toward the center of the stadium,” said Henry Throop, astronomer in the Planetary Science Division at NASA Headquarters in Washington. “From our vantage point, we’ll be able to be to see Jupiter on the inside lane, approaching Saturn all month and finally overtaking it on December 21.”
The timing of the conjunction adds to the spectacle. The winter solstice also occurs on Monday, at 5:02 a.m.
“Conjunctions like this could happen on any day of the year, depending on where the planets are in their orbits,” said Throop. “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 two planets have been getting closer in our view of the sky over the past few months. While the two planets will have the appearance of being very close to each other, in reality, they will be hundreds of millions of miles apart.
Due to the brightness of Jupiter, it may be difficult to see Saturn. Binoculars will help, but if you have a telescope, you may be able to see some of the moons around those planets.
But this will only be visible locally if the weather cooperates. A disturbance traveling through Virginia late in the day may increase the clouds during the evening, especially north of Richmond.