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This December, you can see the “greatest conjunction” of Jupiter and Saturn – a.k.a. the closest visible gathering of these planets in 800 years!
On December 21, 2020, the two bright planets will appear so close that they will fuse into a single dot of light.
Every 20 years, the planets Jupiter and Saturn appear close to each other in the night sky. A gathering of any two planets is called a conjunction; a gathering of Jupiter and Saturn, the rarest gathering of any planets visible without a telescope, is called a “great conjunction.” Usually when these planets conjunct, they are at least one degree apart, which is twice the width of a full moon. On December 21, 2020, however, they will appear only 0.1 degrees apart, or about one-fifth the width of a full moon. That is so close that it’s quite possible the two planets will appear as a single, brilliant dot of light!
This also means that both planets will appear in the same view in a telescope. You will be able to see the fabled rings of Saturn and the four large moons orbiting Jupiter in a single glimpse in the telescope.
So what is the best way to view the great conjunction?
On the night of December 21, 2020, look to the southwest starting around 5:20 pm, or about 50 minutes after sunset. Make sure you have a clear view to the southwest, with no buildings or trees to block your view. The two planets appear low in the sky as it gets dark.
Jupiter, the brightest dot of light in the December 2020 evening sky, outshines every star. Saturn will appear either as another bright light just to the upper right of Jupiter, if you can tell them apart at all; or the two planets may appear fused into a single dot of light. As it gets dark around 5:30 pm, the two planets will be only about 12 degrees above the horizon, which is the width of your palm held at arm’s length. The two planets set at about 6:45 pm on December 21, so your window to view the conjunction is from about 5:20 to 6:45 pm.
Is this the closest conjunction in 400 years, or 800?
The December 2020 event is the closest gathering of these two planets since 1623. However, since the 1623 conjunction occurred when Jupiter and Saturn were virtually lost in the light of the setting sun, there is a good chance that no one ever saw that conjunction! With a telescope, which Galileo had invented 14 years earlier, it might have been possible to see Jupiter and Saturn, though there are no records of that occurring. Research indicates that, indeed, no humans saw the 1623 conjunction.
For this reason, it seems the conjunction of March 4, 1226 is actually the most recent time in which such a close conjunction of Jupiter and Saturn was actually visible to humans. This occurred well before sunrise and was clearly a case where the two planets, separated by only one-twentieth of a degree, would be seen as a single dot of light.
Interested in more space stories like this one? Catch a show in LSC’s Jennifer Chalsty Planetarium, the biggest planetarium in America. Click here to see what’s playing, get showtimes, and purchase tickets.