“Christmas Star” of 2020

[Mystic Wanderer]

December 21, 2020, will bring us a cosmic event that hasn't happened since 1623, but it couldn't be easily observed because they were facing the sun. The last time this happened where it could be seen was almost 800 years ago, during the great conjunction of 1226! 

Wow! I know what I'll be doing tomorrow just before sunset. Seeing this is a "once-in-several-lifetime's" event!

If you can see it, please take pictures in case it's too cloudy for the rest of us to capture the event.

The year 2020 will end with a special astronomical event: the closest great conjunction of Jupiter and Saturn in 397 years. On December 21, the two planets will almost touch in the sky.


Night Sky Map: find Saturn and Jupiter in the sky

What Is a Conjunction?

Generally speaking, a conjunction is when two objects appear close to each other in the sky. A conjunction of Jupiter and Saturn—which only happens about once every 20 years—is called a great conjunction.

In the technical language of astronomers, there are a number of ways to define a conjunction. One way is to say it is the moment of minimum separation between two objects as viewed from the Earth. By this definition, the 2020 great conjunction of Jupiter and Saturn will occur at about 18:20 UTC on December 21. Convert to your time zone

What Can We See, and When Can We See It?
Since September 2020, Jupiter has been moving closer and closer to Saturn in the early evening sky. Wherever you are in the world—even in light-polluted urban environments—the two planets are an impressive sight, and easy to find after sunset. If you're in the Northern Hemisphere, look toward the southwest. If you're in the Southern Hemisphere, look toward the west. Jupiter is the brighter of the pair.

As November begins, Jupiter and Saturn are five degrees apart, which is the width of your three middle fingers held at arm's length. (Another way to think about angular distances in the sky is to remember that the Moon's size is about half a degree.) At the start of December, the planets will be two degrees apart, and still moving closer together.

A handy guide to measuring the sky
A few days before December 21, a thin Crescent Moon will pass close to Jupiter and Saturn in the sky. In the Western Hemisphere, the Moon will be closest to the two planets on December 16. In the Eastern Hemisphere, it will be closest on December 17.


On December 16 and 17, Jupiter and Saturn will be joined by a thin Crescent Moon. This is our Night Sky Map for New York City on December 16, about 45 minutes after sunset.



Just 0.1 Degrees Apart on December 21
On December 21, the day of the conjunction, Jupiter and Saturn will be separated by a mere 0.1 degrees, and may appear as a single bright “star.” The two planets are completely merged together on our Night Sky Map for this date, although a careful observer should be able to separate them in the sky with the naked eye.
The pair of planets will become visible at twilight, close to the southwestern horizon in the Northern Hemisphere, or the western horizon in the Southern Hemisphere. They will set within a couple of hours or so, so it is important to have a clear view toward the horizon.

Jupiter and Saturn will continue to be an impressive sight in the early evenings following December 21. During January 2021, however, the two planets will become lost in the glare of the Sun.
“Christmas Star” of 2020
As Jupiter and Saturn will rendezvous just a few days before Christmas, forming what will look like a single bright object in the sky, the 2020 great conjunction is sometimes also called the “Christmas star” or “Bethlehem star.”
In fact, some scholars have theorized that the original Christmas star, known as the Star of Bethlehem, might also have been a great conjunction. According to Christian lore, a bright light in the sky led the Three Wise Men to the location of Jesus's birth. Other theories aiming to explain this biblical phenomenon include a supernova explosion and a comet.
Some media outlets have also referred to the phenomenon as “kissing stars” or “double planets.”

Closest Great Conjunction since 1623
The December 21, 2020 conjunction will be the closest great conjunction since July 16, 1623. At the great conjunction of 1623, Jupiter and Saturn were slightly less than 0.1 degrees apart. However, this event would have been difficult—although not impossible—to observe since the two planets were near the Sun.
The last time that the two planets were easily observable when separated by less than 0.1 degrees was almost 800 years ago, during the great conjunction of 1226.

 
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