Jupiter and Saturn have flirted with each other for months. For almost all of 2020, they’ve been separated by no more than 10 degrees — the width of your fist held at arm’s length. This month, though, the giant planets will outdo themselves. On the 21st, they’ll pass less than half a degree apart. The last time they appeared closer was in 1623.

Jupiter and Saturn pass by each other once every 20 years. It takes that long because the planets are far away from the Sun.

On average, Jupiter is almost half a billion miles from the Sun. At that range, the planet takes almost 12 years to complete a single orbit around the Sun. So as we watch from Earth, that’s also how long it takes for Jupiter to make one lap against the background of stars.

Saturn is almost twice as far from the Sun. Not only does that mean that Saturn has to travel a longer distance around the Sun, but it moves slower than Jupiter does. So it takes Saturn about 30 years to circle the sky.

Put those motions together, and it means the planets get close once every 20 years.

Look for Jupiter and Saturn in the southwest as night falls. Jupiter is the brighter of the two — brighter right now than anything else in the sky at that hour. Saturn is a couple of degrees to the upper left — the width of a finger at arm’s length. Watch as the gap between them closes evening by evening — leading to their magnificent conjunction on the 21st.

Script by Damond Benningfield

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