Alignment of Two Major Planets Will Cause Rare ‘Christmas Star’ in December

by Will Shepard
(Photo by Gary Hershorn/Getty Images)

For astronomy buffs, December is bringing a pretty cool event in the night sky. On December 21, 2020, the two biggest planets, Jupiter and Saturn will appear to collide and create one superstar.

In actuality, Jupiter and Saturn will be, visually, exceptionally close for the first time since the Middle Ages. On the winter solstice, the two planets will seemingly create one super beam of light.

Even though the planets will look as if they are on top of one another, they’ll remain far apart. In astronomical terms, they will still be 5 astronomical units apart. An astronomical unit (au) is what astronomers use to measure distances in outer space. One au is approximately 93 million miles, or rather, the distance between the Sun and Earth.

This conjunction – when two planets line up in the sky – between Jupiter and Saturn actually happened a few weeks ago. But, for everyone on Earth, they will line up together. This is because our sightline into the Solar System is skewed as a result of our orbit speed.

Again, on December 21, Jupiter and Saturn will align. This astronomical feat happens roughly every 20 years. However, for Earth to see this happen is exceptionally rare.

Planets Creating a Mega Star

Patrick Hartigan, an astronomer at Rice University, explains why this occurrence is so uncommon.

“Alignments between these two planets [Jupiter and Saturn] 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. You’d have to go all the way back to just before dawn on March 4, 1226, to see a closer alignment between these objects visible in the night sky.”

The distance between Jupiter and Saturn is going to seem smaller than the moon.

Stories as told in the Holy Bible say that the “three wise men” in Christ’s birth journey followed this “great conjunction.”

German astronomer, Johannes Kepler, explains that the story of finding Jesus to give him gifts could have been similar. He says that the kings might have followed a triple conjunction between Jupiter, Saturn, and Venus.

In our night sky, Jupiter and Saturn will come together low on the horizon. In the northern hemisphere, the planets will be visible for about an hour after sunset.

Each night, you can watch the planets get closer together, and on December 21, they will be at their closest. On the solstice, this event will even be bright enough to be seen during twilight.

This feat won’t happen again until March 15, 2080. So, keep an eye on the southwest horizon for Jupiter and Saturn creating one giant star.