The good thing is that the spectacle will be shown worldwide without special equipment. All you have to do is look southwest once a night. And people with an amateur telescope can admire another rarity: with a low magnification, two massive planets can be captured in one and the same field of view. Jupiter, with its four brightest moons, and Saturn with its striking rings will be all in view at the same time.
But you do not need to wait until December 21 to admire the night sky. “It’s a lot more fun to look all month long rather than just December 21,” said Laura Danley, curator of Griffith Observatory in Los Angeles. “You are watching those two lights, Jupiter and Saturn, up close and close, until they are only one-tenth of an arc degree on the 21st” – or about one-fifth of the diameter of the full moon in the night sky.
This is a very short distance, given that you can easily cover the entire lunar disc with the thumb at arm’s length. Nevertheless most night vision goggles will still be able to separate the two planets from each other. “If your vision is good to drive, then you can see that Jupiter and Saturn are two different objects,” even when they are closest to each other, Danley says.
near and far
Astronomers call a moment when planets in the sky appear directly next to each other or even a coincidence. The relations of the gas giants Jupiter and Saturn occur once every twenty years and are called “great conjugates” because of their rarity. Combinations of the inner planets of our solar system, such as Mercury or Venus, with each other or with one of the outer planets, are many times more common per decade.
A planet far away from the Sun, it moves slower than the night sky – and Jupiter and Saturn are two planets away from the Sun and still visible to the naked eye. (Saturn is far from the Sun and smaller than Jupiter, one of the two.) Jupiter takes 12 years to orbit the Sun, while Saturn takes 30 years to do so. Due to those astronomical revolutions, they stand next to each other in the night sky once every twenty years.
But not all yogas of Jupiter and Saturn are equal. Their classes are not in the same disc plane. (If that were the case, Jupiter would have completely blocked our view of Saturn every twenty years.) Generally, two massive planets pass through an arc of only a few degrees, a short distance into the night sky. But this year, the two gas giants will get closer to each other from Earth, even though they are actually hundreds of millions of miles away.
The final coincidence of Jupiter and Saturn occurred near each other in 1623, thirteen years after Galileo first rolled a telescope into the night sky and discovered Jupiter’s four largest moons. “It would have been very difficult to see that conjunction, because both planets would have been closer to the sun in the sky,” said Kevin Schindler of the Lowell Observatory in Flagstaff, Arizona. (The same happened during the last ‘great combination’ in 2000.)
“You have to go back to the year 1226 to find a combination that looks tight and visible at the same time in the night sky.” The next such coincidence will happen in 2080.
Solar system in motion
Throughout history, people have attributed special astrological significance to these types of conjunctions. This is described by the English writer Geoffrey Chaucer in his poetic epic Trillius and crissade Great combination of 1385: “Saturn and Jupiter, in [het sterrenbeeld] Cancer came together / that such rain fell from the sky. “Some astrologers predicted global disasters, but certainly nothing happened.
Today we know that planets draw a little by their gravity, but that their impact on the Earth is negligible. So we can relax and enjoy the show – or try to take pictures of it.
“To get a good picture of the pair,” says Bradley Scheffer, an astronomer at Louisiana State University, “you have to practice a lot and experiment with very good instruments. While your smartphone’s camera can register two points of light in the night sky, people with a single lens digital SLR camera or at least a camera on a tripod will get better results.
“You should use a tripod and plan ahead of time where you want to take photos,” says Schaefer. Make sure that you can see the night sky in the southwest direction without hindrance.
And don’t worry if it’s cloudy, as a host of observatories, including Lowell, Arizona, will broadcast the event on a live stream.
We know that planets are always in motion, but a coincidence really makes us feel again. The great coincidence of 2020 is an opportunity to see the solar system as an ever-changing phase, on which the planets act. “When you look at the night sky for several nights in a row, you realize how dynamic the solar system really is,” Dunley says.
Science journalist Dan Falk lives in Toronto. His publications include Science of shakespeare In In search of time. Follow donation Twitter.
This article was originally published in English on NationalGeographic.com