The Great Conjunction of 2020
On 21 December 2020 Jupiter and Saturn appeared only a fifth of the full Moon’s width apart — the closest easily visible meeting since 1226.
Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
On the evening of 21 December 2020, Jupiter and Saturn drew within 0.1 degree of each other in the sky, only about a fifth of the full Moon’s width. The two planets meet in our sky about every twenty years, but a meeting this close and this easy to see at night had not happened since March 1226, 794 years earlier. They came similarly close in 1623, but then the pair sat so near the Sun that it could hardly be seen.
Low in the south-west after sunset, the two planets looked to the naked eye almost like one bright star. Binoculars split them into two points, and a small telescope could show Jupiter’s four large moons and Saturn’s rings together in one view. Because it came just before Christmas, people called it the “Christmas Star”, and many around the world went out to look at the evening sky.
These meetings arrive as regularly as clockwork. Jupiter takes about 11.9 years to circle the Sun and Saturn about 29.5 years. Each time the faster inner planet, Jupiter, catches up with Saturn, the two appear to line up in our sky, and that happens about every 19.9 years. In most meetings, though, the planets stay about a degree apart, so an approach as close as 0.1 degree comes only once every few hundred years. The next one this close is on 15 March 2080.
In the seventeenth century the astronomer Johannes Kepler suggested that a meeting of Jupiter and Saturn in 7 BC might have been the Star of Bethlehem described in the Bible. The orbit view replays how Jupiter and Saturn line up along the direction seen from Earth, and the sky view shows the two planets side by side in the south-western sky on the evening of 21 December 2020.
Mission goals
A meeting of two planets is the easiest chance to see with the naked eye that planets move. Looking at the same time each evening for a few days, one can watch the two draw closer and then pull apart. Seeing Jupiter overtake Saturn shows directly that planets closer to the Sun travel around it faster.
The 2020 meeting came when COVID-19 made it hard for people to travel far, and it was a sky show that could be enjoyed close to home. Earlier the same month, on the 14th, there was also a total solar eclipse over South America, so the December sky made news more than once. Because it could be seen with the naked eye and no special equipment, many people took their first interest in astronomy.
In the past, such meetings were sometimes seen as signs of things to come. In the fourteenth century, doctors in Paris even blamed the Black Death on a gathering of Jupiter, Saturn and Mars in 1345. Today we know these meetings follow from the planets’ orbits and can be calculated centuries ahead, and the 2020 meeting arrived exactly as predicted.
Mission chronology and background
The planets were closest at 18:20 UT on 21 December 2020. At that moment they were in the evening sky, about 30 degrees from the Sun. In Europe and the Americas the moment itself fell in the evening; in East Asia it had already passed, but the pair could still be seen that evening at almost the same separation.
Comparing past meetings shows why 2020 was special. The meeting of 4 March 1226 was even closer, at about 0.035 degree, and was well placed in the dawn sky. The meeting of 16 July 1623 was also close, at about 0.09 degree, but the planets were only 13 degrees from the Sun and lost in its glare. That is why 2020 is described as the first close and easily visible meeting in 794 years.
21 December was also the winter solstice, which was simply a coincidence. The two planets were in Capricornus, low in the south-west in the early winter evening, and they soon set below the horizon. So they could be seen for only a little over two hours after sunset, and observers needed a spot with an open view to the west.
Where to see it — sky and simulator
Choose the 2020 Jupiter–Saturn meeting in the sky view’s event list to replay the low south-western sky on the evening of 21 December. With a mid-northern city such as New York as the location, the two planets appear pressed together low in the south-west shortly after sunset. In the orbit view, following Earth and moving to the same date shows that the planets overlap in the direction seen from Earth while really lying more than 700 million km apart.
The next meeting is on 4 November 2040, when the planets will be about 1.2 degrees apart. The next one as close as 2020 is on 15 March 2080, and it will be seen in the dawn sky. Select Jupiter or Saturn in the sky view to find where each planet is now and when it rises from your location.
See this for yourself — replay the moment in the orbit view
FAQ
Were the planets really close together?
No. They only looked 0.1 degree apart in the sky; in reality they were more than 700 million km apart.
Why ‘794 years’?
No meeting since 1226 had been both this close and easy to see. The 1623 meeting was close but too near the Sun to be seen well.
When is the next one?
The next meeting is on 4 November 2040, and the next one as close as 2020 is on 15 March 2080.
Was it really the Christmas Star?
It was only a nickname, given because it came near Christmas. Kepler suggested a Jupiter–Saturn meeting in 7 BC as a possible Star of Bethlehem.
Related
- Total eclipse — South America (2020)
- JUICE launch — to the icy moons
- Shoemaker–Levy 9 hits Jupiter
- Jupiter — object index
- Saturn — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.