What Exactly Is the "Christmas Star" That's Set to Appear on December 21?

Since 2020 has been such a unique and history-making year, it's only fitting that it concludes with a unique space event that only occurs every few decades.

Each year, on Dec. 21, the Winter Solstice marks the shortest day of the year in the Northern Hemisphere (while it is considered to be the Summer Solstice, with the longest day of the year, in the Southern half of the world). It also officially ends the fall season and marks the beginning of winter.

In 2020, a rare planetary crossing is set to take place on Dec. 21, and many are referring to the event as the "Christmas Star."

What happens on December 21? Find out what you can expect to see during the Winter Solstice and when you should be on the lookout.

Many people have been discussing the appearance of the "Christmas Star" (also known as the Great Conjunction) on Dec. 21, but what exactly does that mean? Will it be clear to the naked eye?

On that date, Saturn and Jupiter are set to align. It will appear as if the two planets are actually one during that time, though they are actually still millions of miles apart. 

The Dec. 21 great conjunction comes seven weeks after the heliocentric conjunction, which was when both planets shared the same heliocentric longitude.

Jupiter has a 12-year orbit, while Saturn's trip around the Sun takes 29 years. Based on these disparate orbit lengths, it is a rarity for the two to line up and cross paths. 

This alignment occurs every 20 years, and the last one took place in May of 2000. But, during the most recent Great Conjunction, it was difficult to see the planets "intersect" because of their position in the sky.

The 2020 Christmas Star is different from anything that any living being on Earth has seen before. Jupiter and Saturn will appear to be much closer together than they have since 1623 — which was when astronomer Galileo Galilei was alive to see it. 

According to records from the 1623 Great Conjunction, Saturn and Jupiter lined up too close to the sun, which made it rather difficult for people to look at. 

The last time the planets aligned in a manner that was so visible to onlookers was actually in March of 1226.

Considering what a banner year 2020 has been for so many people, it only seems appropriate that it wraps up with a rare out-of-this-world event. 

If you're now regretting not pulling the trigger on a telescope purchase, don't fret. The 2020 great conjunction can be seen with the naked eye (though the planets would appear to be more unified with the aid of a telescope or binoculars).

You can begin to look for the alignment of the planets in the lower Southwestern portion of the sky beginning about an hour after sunset on Dec. 21.

The event is set to officially begin at 6:20 UT (Universal Time).  

If you miss the 2020 great conjunction, then you'll just have to wait until 2080 to see one with a similar magnitude.