What's Up With Jupiter and Saturn?

Conjunction junction, what’s your function?

Nah, not that kind of conjunction. A planetary conjunction is when two planets appear near each other in the sky. On December 21, 2020, Jupiter and Saturn will appear near each other in the sky. They will not actually be near each other; they will still be 735 million kilometers apart from each other!

Why do they look like they’re near each other?

Eight planets orbit the Sun in their own not-quite-circular orbits. Earth is the third planet from the sun, Jupiter is the fifth, and Saturn is the sixth. The three planets might look like the picture below, in relation to each other. They are actually much, much farther apart than it is possible to draw on a webpage, so keep that in mind.

Every once in a while (every 20 years or so), Jupiter and Saturn pass each other when viewed from the Earth. That is, to someone standing on Earth, Jupiter and Saturn look like they’re in line with each other, or nearly so. It’s like watching two people walk down the sidewalk at different speeds, with the slower person up ahead. At some point, the faster person will pass the slower person. If you were watching this from the other side of the street, the moment they pass, it looks like they’re in the same exact place as each other, even though you know they’re not actually in the same exact place. That is what’s going on with Jupiter and Saturn.

This year, the conjunction is especially interesting, because Jupiter and Saturn appear to be closer than they have at any point since 1623 and the closest observable (i.e. without a telescope) since 1226. That’s because each planet’s orbit is slightly tilted compared to the other planets’ orbits. The picture below shows an example of a conjunction which, due to the tilted orbits, is not as spectacular as the one in 2020. The tilts are exaggerated in the picture, but because the distances are so much bigger than in the picture, even a small (~1 degree) difference in tilt can cause the planets to appear farther apart.

In the 2020 conjunction, Jupiter and Saturn will appear close enough together that they might look like one mega-planet in the sky. It might even be visible without a telescope!

Missed it? Set your alarm for the next extra-close conjunction of Jupiter and Saturn on March 15, 2080.

Source: https://earthsky.org/astronomy-essentials/great-jupiter-saturn-conjunction-dec-21-2020