This is pretty awesome.

On December 21, for the first time since 1226, the “Christmas Star” (that told the Maji of Jesus’ birth) will be visible in the night sky. The Earth, Jupiter, and Saturn will be lined up in a row with Jupiter and Saturn appearing incredibly close, creating what some astrophysicists believe is the Christmas Star.

From Forbes:

If you managed to see the crescent Moon pass Jupiter and Saturn this week, you’ll have noticed something else about the Solar System’s two largest planets.

They’re now really, really close to each other, and on December 21, 2020—the date of the December solstice—they’re going to almost appear to collide to become one super-bright point of light.

Jupiter and Saturn will look like a “double planet” for first time since Middle Ages.

In reality, of course, they won’t be close at all. Think about the distance from the Earth to the Sun. That’s what astronomers call an astronomical unit (au), and it’s how they measure distances in the vastness of the Solar System. Jupiter is 5 au from us. Saturn is 10 au.

These two planets aligned in the Solar System a few weeks ago, but on December 21 they’ll appear aligned to us on Earth. Our line of sight is different because we’re orbiting quickly around the Sun.

“Alignments between these two planets are rather rare, occurring once every 20 years or so, but this conjunction is exceptionally rare because of how close the planets will appear to be to one another,” said Patrick Hartigan, astronomer at Rice University.

“You’d have to go all the way back to just before dawn on March 4, 1226, to see a closer alignment between these objects visible in the night sky.”

Jupiter and Saturn’s orbital resonance is such that they align in a “great conjunction” every 19.6 years, but they’re rarely as close—from our point of view on Earth—as on December 21, 2020 when the two planets will be separated by less than the apparent diameter of a full Moon.

conjunction is when two objects line up in the sky.

Though some astronomers think the Star of Bethlehem was actually a trifecta with Jupiter, Saturn, and Venus all in perfect alignment.

A further explanation:

 

 
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