Jupiter and Saturn are expected to close together very much in December, when they form a rare “double planet” phenomenon.

The last time this event was about 800 years ago.

The two planets also came close to each other in the 17th century, but the event is not said to be visible from Earth.

The celestial event is called the Great Conjunction, and it is expected to happen on December 21, when Jupiter and Saturn will be only 0.06 degrees from each other, about 1/5 of the diameter of the full moon.

“The alignments between these two planets are rather rare because of how close the two planets are to each other,” said Patrick Hartigan, astronomer at Rice University.

If this were to happen, he would see this conjunction with the naked eye as if it were a large, bright star.

And if the sky was clear on December 21, it would be visible all over the world.