Jupiter and Saturn will get very close to one another on Winter Solstice to form a rare phenomenon known as ‘Christmas Star’ or ‘Star of Bethlehem’.

“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,” Patrick Hartigan, an astronomer at Rice University, told Forbes.

Jupiter and Saturn will look like a ‘double planet’ for the first time since the Middle Ages, Forbes reported.

It’s a ‘once-in-a-lifetime’ sighting of this proportion, which won’t occur until 2080 and then sometime after 2400.

Stargazers will be able to enjoy this rare phenomenon across the world.

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Gazing into the south-western horizon at the right time, one would be able to witness the two gas giants, which will look like neighbouring points of light.

The best time to witness the ‘Christmas Star’ on Winter solstice would be between dusk and about 15-20 minutes after dark.

NASA has informed that the conjunction will appear ‘spectacular’ with a normal telescope or even the naked eye.

According to NASA, on December 21, the planets will appear just a tenth of a degree apart, which is equivalent to the thickness of a dime held at arm’s length.

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“This event is the greatest great conjunction between Jupiter and Saturn,” said NASA.

In astronomical terms, conjunction is when two objects line up in the sky.

It hasn’t been seen for last 800 years. One will have to go all the way back to just before dawn on March 4, 1226, to see a closer alignment between the two planets.