On the night of the winter solstice (Dec. 21), a rare cosmic event known as planetary conjunction will occur and, for a few moments, Jupiter and Saturn will appear to shine in the night sky as one bright double planet.
According to NASA, the fact that the conjunction is taking place during the winter solstice is purely coincidence. Nevertheless, the event has been dubbed the “Christmas Star.”
About the conjunction
The space agency reports that a conjunction takes place when two planets appear to meet and overlap one another from Earth’s perspective. In reality, the planets are still hundreds of millions of miles apart in space.
Henry Throop, an astronomer in the Planetary Science Division at NASA, recently explained the phenomenon in a statement. He said (via People):
- “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. ... From our vantage point, we’ll be able to see Jupiter on the inside lane, approached Saturn all month and finally overtaking it on Dec. 21.”
What do you get when you cross two gas giants? A cosmic kiss!— Canadian Space Agency (@csa_asc) December 20, 2020
Jupiter and Saturn will meet in the southwestern sky after sunset on December 21. The two planets haven’t appeared to be this close since 1623.
Photo: Pete Lawrence pic.twitter.com/44qgtTBIIP
According to NASA, planets appearing to pass each other in the solar system is a fairly regular occurrence, and Jupiter and Saturn are aligned in the sky about once every two decades.
But this year’s conjunction is truly special as the planets will be passing each other more closely than they have in nearly 400 years. Saturn and Jupiter will be positioned just a tenth of a degree apart, and for the first time in nearly 800 years, this close alignment will happen at night.
On the night of the solstice, the two planets will appear so close that a pinkie finger at arm’s length will easily cover both planets in the sky.
“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,” astronomer Patrick Hartigan, a professor of physics and astronomy at Rice University in Houston, in a statement (via CNN).
TOMORROW Jupiter and Saturn will be at their closest separation in the sky since 1623 at 0.1° apart. Here's an animation showing exactly how close that is relative to a familiar object, the Moon! (Moon ONLY added to illustrate the scale) #GreatConjunction2020 pic.twitter.com/2mvdl6KjmI— Dr. James O'Donoghue (@physicsJ) December 20, 2020
How to watch it
NASA provided stargazers with three quick tips to make the most out of the upcoming conjunction. The space administration recommends:
- Be sure to find a spot with an unobstructed view of the sky, such as a field or park. Jupiter and Saturn are bright, so they will be visible from most cities.
- An hour after sunset, fix your view toward the southwestern sky. Jupiter looks like a bright star and is easily visible. Saturn is slightly fainter and is positioned slightly above and to the left of Jupiter leading up to the conjunction, then Jupiter will overtake Saturn and the two planets will reverse positions in the sky.
- While both planets can be seen with the unaided eye, binoculars or a telescope can help stargazers see Jupiter’s four large moons orbiting the giant planet.