For daily wit & wisdom, sign up for the Almanac newsletter.
A rare, spectacular sky event is about to unfold: the greatest conjunction ever! It will be more impressive than the usual celestial headliners, like lunar eclipses and Mercury transits. And it will be visible around the world. On the very day of the solstice, December 21, 2020, Jupiter will come as close to Saturn as Jove’s own moons!
When Jupiter and Saturn—the two biggest planets in our solar system—meet, it’s termed the “Great Conjunction.” What’s even more special is that it’s happening on night of the winter solstice.
Our two biggest worlds will appear closer to each other than they have in centuries, as if they are touching in the night sky above. You can think of it as a double planet. To some, it may appear as a very bright “Christmas Star.” How fitting for the season!
It’s already making headlines in the astrological world. After all, from time immemorial, a meeting of Jupiter and Saturn was deemed the most auspicious of all planetary get-togethers, the only one called a “Great Conjunction.” There was good reason for such attention: This is the rarest meeting between any of the five bright planets. It happens just once every two decades, and 2020 brings the closest Jupiter-Saturn conjunction since 1623, during Galileo’s times.
Jupiter-Saturn meetings were believed to have numerous earthly effects, none of them good. One famous consequence was that presidents supposedly suffered risks for their very lives if they were elected or in office when these planets met, and the Web offers no shortage of astrological tables making such a purported case.
But this is an astronomy—not astrology—page, so we will focus on how to view the event and how it compares with past and future Great Conjunctions.
What Is a Conjunction?
Simply speaking, a conjunction occurs when planets or other objects appear to be very close to each other on our sky’s dome. These “meetings” or conjunctions in the sky are fairly frequent, especially when it comes to the Moon passing the different planets in the sky.
However, a conjunction of Jupiter and Saturn is rare and only happens once every 20 years. And December 21, 2020, brings the closest great conjunction of Jupiter and Saturn in 397 years. From our point of view, the two giant worlds will appear only 0.1 degrees apart. That’s just 1/5 of a full Moon diameter. Unlike previous conjunctions, this one’s not obscured by the Sun’s glare, either.
Past and Future Conjunctions
It’s important to get the details right, since its once-per-20-year incidence may make this event seem more common than it really is. For example, during the last Great Conjunction in May 2000, the planets never came anywhere as close together as they will this month, and, moreover, were closer to the Sun and partially hidden in solar glare. It wasn’t eye-catching.
The same was true the time before, in December of 1980. You’d have to go back to February of 1961 to remember a Great Conjunction that remotely competed with the one this month. But even that was far inferior to the 2020’s Great Conjunction.
Nor, looking ahead, will we get another chance anytime soon. The one in October, 2040 won’t be very good at all, with the planets fairly widely separated, and the same will be true in October of 2060.
Only if you can hold out until March 15, 2080, will you see a Great Conjunction as good as this one. Actually, that one, low in the eastern sky before dawn, will even be better, since the two giant planets will seemingly merge into a single brilliant star or rare double planet. Which is what some are saying about our current Great Conjunction.
A Single “Star” on December 21
The truth? Well, if you skipped your last optometrist appointment, you might indeed perceive the two planets as a single brilliant object. But those with normal vision should see them extremely close together, but as separate-looking “stars,” with Jupiter brilliant and Saturn as merely bright.
No matter because here’s some more good news: Unlike most such conjunctions, the pair will stand adequately separated from the sun’s glare, and be sufficiently high enough for it to not present a problem. Yes, they’ll be low in the southwest a half hour after sunset on December 21. But they won’t be super-low—15° above the horizon.
Still, if you’ve got trees or neighbors’ houses or hills in the direction of sunset, you’ll want to check out the planets a few evenings beforehand at that same time so you can be sure they’ll be in the clear on the solstitial evening. If they’re blocked, walk or drive to an unobstructed place like a field, cemetery, or lakeside.
A One-Night Affair
Unfortunately, this will be a one-night affair. The day before and the day after, the planets will be noticeably farther apart and nowhere near as striking. So if the weather cooperates on the 21st, you’ll want to get all you can out of the spectacle. Binoculars will be a nice adjunct, and will easily reveal Jupiter’s four huge satellites spread in a straight line. Saturn will be off in a different direction, perpendicular to those moons.
If you have a small backyard telescope, or can join a friend with one, or can contact your local astronomy club so that you can get a view through a telescope, well, now you’ll be truly amazed. Because the two largest planets in our solar system will be there in the same medium-power telescope field! That’s a stunning sight no one alive has ever seen.
But remember, this is not an occurrence that’s threatening in any way. They seem close together, but Saturn is actually far behind Jupiter—twice as distant, in fact—so those giant worlds are actually nowhere near each other.
How to View the Great Conjunction
To review: Jupiter and Saturn will perform their Great Conjunction lowish in the southwest on December 21, the day of the solstice.
If you wish, start watching a few days prior. On December 16, soon after sunset, look for the crescent Moon in the southwest sky. Right above the Moon are the two bright planets. You can’t miss it.
On December 21, the day of the conjunction, make sure you have a clear view of the southwestern horizon near sunset since the planets will be pretty low in the sky.
The Sun will have just set at its leftward-most spot on your horizon of the entire year, and your best planet view starts about half an hour after your local sunset.
The Great Conjunction’s viewing will begin around 5 PMin most places.
They’ll remain visible for another hour after that if you have no obstructions like hills, so you’ll have plenty of time for leisurely observations.
Of course, you don’t want to be too leisurely—when you remember that this will also be the end of the world.
Just kidding, of course! If it’s not enough that astronomers don’t believe one word of the conjunction fears, just recall that we had no problems with those 2000 and 1980 Great Conjunctions. Still, it does somehow seem fitting that this very strange year should wind down with one of the sky’s rarest celestial events.