Jupiter and Saturn will look like a double planet for first time since the Middle Ages
Just after sunset on the evening of Dec. 21, Jupiter and Saturn -the largest planets in our solar system-, will appear closer together in Earth’s night sky than they have been since the Middle Ages (the last time they orbited as closely as they will tomorrow and were visible in the sky, was on March 4, 1226).
“On the evening of closest approach on Dec 21 they will look like a double planet, separated by only 1/5th the diameter of the full moon,” said Patrick Hartigan, a professor of physics and astronomy at Rice University. “For most telescope viewers, each planet and several of their largest moons will be visible in the same field of view that evening.”*
“Those who prefer to wait and see Jupiter and Saturn this close together and higher in the night sky will need to stick around until March 15, 2080,” Hartigan said. “After that, the pair won’t make such an appearance until sometime after the year 2400.”*
These two gas giants are made mostly of hydrogen and helium with no solid surface; they have satellites, rings, and giant magnetospheres. Jupiter’s satellites or moons ( Io, Europa, Ganymede, and Callisto, the largest of its 63) are more massive -except for one, Titan-, than the 47 moons of Saturn.
Enjoy the celestial show.
* https://news.rice.edu/2020/11/19/christmas-week-worlds-will-align-for-spectacular-heavenly-sight-2/