The Great Conjunction of 2020: Jupiter and Saturn sky show this fall

A waxing moon joins the two bright planets again tonight.

Southern evening sky in late September
Southern evening sky in late September
NASA via earthsky.org

There’s a spectacular sky show in the southern sky this fall.

It’s called the Great Conjunction. Saturn and Jupiter are bright in the southern sky on clear evenings. The waxing moon adds to the show tonight hanging to the lower left of Saturn.

Southern sky for the evening of September 25, 2020
Southern sky for the evening of Sept. 25, 2020
Courtesy NASA/JPL-Caltech

Earthsky.org elaborates:

On September 23, 24, 25 and 26, 2020, look for the moon in the evening sky, and it’ll guide you to Jupiter and Saturn, our solar system’s two biggest gas giant planets. Given clear skies, you can’t miss these bright worlds. The moon is the second-brightest celestial object, after the sun. And Jupiter is exceptionally bright, too, outshining all the stars (but just a hair less bright than dazzling Mars; more about Mars below). As for Saturn, it’s as bright as the brightest stars. Plus Jupiter and Saturn are noticeable now for their nearness to each other. They’re headed for a great conjunction before 2020 ends.

The Great Conjunction of December 2020

Jupiter and Saturn are 7.5 degrees apart in the southern sky now. They will draw closer this fall and will be just 0.1 degrees apart on the winter solstice on December 21.

Astro Bob writes for the Duluth News Tribune about how the two planets draw closer until conjunction on December 21.

More distant Saturn orbits at 21,675 mph (9.7 km/sec) and takes 29 years to circle the sun. Because Jupiter is both closer to the Earth and travels faster it overtakes Saturn about once every 20 years, an event called a great conjunction.

Because the orbits of Jupiter and Saturn are tilted slightly with respect to Earth's orbit, 1.3° and 2.5° respectively, when they do line up the distance between them varies, making every conjunction different. If they were in exactly the same plane Jupiter would always pass directly in front of Saturn, but that's extremely rare.

Enjoy the amazing sky show on clear evenings this fall.

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