Jupiter Saturn conjunction: how to see today’s ‘poinsettia’

Get ready for December 21, 2020, when the “great winter solstice conjunction” of Jupiter and Saturn has brought them closest in the night sky since 1623

Tonight, stargazers around the world will be treated to an event that, on average, only happens once every 19.6 years. On December 21st, the winter solstice, Jupiter and Saturn appear in the same place in the night sky in an event known as the great conjunction.

These two so-called gas giants in our solar system, which are normally bright enough to be seen with the naked eye from the light-polluted heart of a city, will align themselves when viewed from Earth to look like an extremely bright planet. That year, the pair will be only 0.1 degrees apart in the sky, making it the next event since 1623. For reference, the diameter of the full moon in the sky extends 0.5 degrees as we see it from Earth. The next time these planets become visible this close to the night sky will be in 2080.

Jupiter and Saturn are the most distant planets that are easy to see with the naked eye. Uranus is only visible this way when the skies are particularly dark, and you will always need binoculars or a telescope to see Neptune.

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Since Jupiter and Saturn are the furthest away from the Sun of all planets with the naked eye, they orbit the slowest. It takes almost 30 years for Saturn to make a round of the Sun while Jupiter takes about 12 years. This is why conjunctions between the two are the rarest between any clearly visible planet.

Where can you look for the great conjunction?

While the event itself takes place on December 21st, the planets will be close to the sky in the days before and after. To see the conjunction, once the sun goes down, look southwest and find the brightest thing you can see. Since the time coincides with the winter solstice, the shortest day of the year in the northern hemisphere, sunset is early. Jupiter and Saturn are low in the sky and setting in quickly. So make sure you have a good view of the western horizon to catch them.

If you have binoculars on hand, the two will appear as separate planets. Saturn is located above and to the left of Jupiter in the northern hemisphere and below and to the right of it in the southern hemisphere.

However, if your binoculars are powerful enough and have a minimum magnification of seven, you can even get a glimpse of Jupiter’s four Galilean moons. In the northern hemisphere there are two of them, Callisto and Ganymede, to the left of Jupiter. To Jupiter’s right, much closer to the planet, one could see Io and Europe. In the southern hemisphere, the moons will point in the opposite direction.

For stargazers with a telescope, if you can spot the planets before they dive too deep on the horizon, and you won’t be lucky enough to see them often, the view is well worth it: Saturn, its rings and some of its moons along with Jupiter , its great red spot and the Galilean moons, all visible at once.

Stargazing at Home comes out every four weeks

These articles are published every week at newscientist.com/maker