The Great Conjunction of 2020
Jupiter and Saturn appeared just 0.1° apart — the closest since 1623.
The moment of The Great Conjunction of 2020: https://nowsky.org/e/great-conjunction-2020 — opens at the right place and time, replayable, no login.
Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
On the evening of 21 December 2020 — the solstice — Jupiter and Saturn drew within 0.1 degree of each other, a fifth of the full Moon's width. The two planets had not met this closely in a visible sky since March 1226, 794 years earlier; a similar approach in 1623 was lost in the Sun's glare.
Low in the south-west after sunset the pair looked to the naked eye like a single bright star, and one binocular field held Jupiter's four Galilean moons and Saturn's rings together — a once-in-a-lifetime composition. Nicknamed the "Christmas Star", it drew crowds to evening skies worldwide.
The rhythm of great conjunctions is clockwork: Jupiter takes 11.9 years and Saturn 29.5 to circle the Sun, so they meet in the sky about every 19.9 years. Most meetings are a degree or so apart; a 2020-class approach to 0.1 degree comes only every few centuries. The next as close is 15 March 2080.
In the seventeenth century Kepler calculated that a triple conjunction of Jupiter and Saturn in 7 BC might have been the Star of Bethlehem. The orbit view replays the geometry of the two orbits overlapping along the line of sight, and the sky view reproduces the south-western sky of 21 December 2020.
Why it matters
A conjunction is the easiest way to see planetary motion with the naked eye. Over a few days the two planets visibly close and separate, and the direction in which Jupiter overtakes Saturn shows intuitively that inner planets move faster — Kepler's third law in plain sight.
The 2020 conjunction was the peak of pandemic-era public astronomy. Coming in the same month as the 14 December eclipse, the south-western evening sky was the talk of December, and sales of binoculars and small telescopes surged; that interest fed the eclipse crowds of 2023 and 2024.
Historically the great conjunction is where astrology and astronomy parted ways. Kepler's Star of Bethlehem hypothesis and medieval Europe's reading of conjunctions as omens of plague concern the same phenomenon; 2020 was the modern confirmation that it is predictable orbital mechanics.
How to watch
Choose the 2020 conjunction in the sky view's event list to replay the evening of 21 December low in the south-west — an hour after sunset, some 15° above the horizon, Jupiter and Saturn pressed together. With Seoul as the location the best time was around 6 pm.
Follow Earth in the orbit view with Jupiter as the gaze target and move the time to 21 December 2020 to see the geometry — Jupiter and Saturn overlapping along the line of sight from Earth while actually more than 700 million km apart.
The next great conjunction is 2 November 2040 (1.1° apart), and the next as close as 2020 is 15 March 2080. Select Jupiter or Saturn in the sky view for their positions and rise times from your location now.
See this for yourself — replay the moment in the orbit view
Background
Closest approach came at 18:20 UT, with the planets 30° from the Sun in the evening sky. Europe and the Americas had the moment itself in the evening; Asia saw the pair a few hours later at almost the same separation.
The conjunction of 4 March 1226 was closer at 0.03°, and that of 16 July 1623 (0.09°) was only 13° from the Sun and effectively unobservable — hence "794 years" for the last one in a visible sky.
21 December 2020 was also the solstice. The coincidence is just that; the planets lay in Capricornus, which put them low in the south-west in early winter evenings and kept the viewing window short.
Viewing conditions for a great conjunction depend on how far the planets stand from the Sun. On 21 December 2020 they were 30° from the Sun and visible for a little over two hours after sunset — the best since 1226. The conjunction of 15 March 2080 has a 0.1° separation 44° from the Sun in the dawn sky, better than 2020, and in August 2417 the pair closes to 0.05°. At the moment Jupiter overtakes Saturn the two planets appear to move side by side in the same direction within one field of view.
FAQ
Were the planets really close?
No — they appeared 0.1° apart in the sky but were actually more than 700 million km apart.
Why 794 years?
No conjunction since 1226 had been both this close and observable; 1623 was too near the Sun.
When is the next one?
The next conjunction is 2 November 2040; the next as close as 2020 is 15 March 2080.
Was it really the Christmas Star?
Only a nickname. Kepler proposed the triple conjunction of 7 BC as a candidate for the 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.