Keep a watch out during the afternoon of December 21, because Jupiter and Saturn are set to align so that they appear to be one giant star. Binoculars should be enough to show a separation between the two, while a telescope will reveal Saturn's rings, Jupiter's belts and both planets' moons, all in the same view.
But what makes the Great Conjunction this year extra special is the fact that Jupiter and Saturn have not been this close to one another in the sky since 1623 - nearly 400 years ago. However, back in 2000, Saturn and Jupiter did align but they did not appear as close together.
Every 20 years the gas giant Jupiter and Saturn cross paths in the night sky during a so-called Great Conjunction. We don't really know what the star of Bethlehem was, but because it was very possibly a conjunction some do refer to this conjunction as the "Christmas Star". On the 21st, Jupiter and Saturn will approach to just one-fifth of the diameter of the full moon, and fainter Saturn might become lost in the glare of brilliant Jupiter, creating an illusion of them merging.
Jupiter and Saturn will appear closest together shortly after sunset on Monday December 21, 2020.
On the night of December 21, Jupiter will lie 551.1 million miles from Earth, and Saturn almost twice as far: 1.0 billion miles.
An hour after sunset, look to the southwestern sky.
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Beginning on December 16, the two will appear closer than the width of the full moon and will appear as a double planet. But on December 21, they will be a mere 1/10th of a degree apart.
The last observable Great Conjunction was on March 5, 1226.
"Nonetheless, the view from here on Earth looks like a spectacular near-miss of the two largest planets in our solar system".
As far as seeing the culmination of all this celestial moving about, the Christmas Star, on the 21st, Chicago's ABC-7 News says "you'll want to look to the lower southwest sky on the evening of December 21, right after sunset". The best spots are from the western sides of the city, with unobstructed views.
"Conjunctions like this could happen on any day of the year, depending on where the planets are in their orbits", said Henry Throop, an astronomer in the Planetary Science Division at NASA Headquarters in Washington. Saturn will be slightly blurred, slightly above and appearing to the left of Jupiter. This means they line up in our sky less frequently than other planets and was therefore the rarest conjunctions people can view naked eye. Jupiter and Saturn conjunctions happen every 20 years.