After sunset on the 2020 winter solstice, many eyes will be looking up to see a 'Christmas Star.'
Both Jupiter and Saturn will get visibly closer to one another throughout December, with their closest alignment expected just after sunset on Monday, December 21st.
HOW CLOSE WILL JUPITER AND SATURN BE
We can measure the visible distance between two objects in the night sky by degrees. Jupiter and Saturn will be about 0.1 degree away from each other, making them appear basically as one bright light in the sky. For perspective, the width of the full moon is about 0.5 degrees. The distance between Jupiter and Saturn from our perspective will be about 1/5 the width of a full moon.
HOW TO SEE IT
In the northern hemisphere, just after sunset, look in the southwest sky and you'll be able to see the two neighboring lights above the horizon. For many Americans, by 7-8 PM local time, the two lights will disappear below the horizon. While looking in the SW sky, Jupiter will be on the left and Saturn will be on the right.
However, you can see Jupiter and Saturn close to one another throughout the month of December above the SW horizon for a couple hours after sunset. The closest alignment will be on Monday, December 21st.
HOW RARE THIS EVENT IS
When two objects in the night sky appear close to one another, astronomers call this a "conjunction." The conjunction of Jupiter and Saturn takes place roughly every 20 years. However the last time these two came within a 0.1 degree of each other, was back in 1623. Humans could not see this conjunction as well because the two planets aligned near the sun, blinding us from any chance of seeing this.
The last "observable" time the two planets lit up the night sky as one bright light was almost 800 years ago in 1226. Here is what Patrick Hartigan, an astronomer at Rice University told Forbes:
“Alignments between these two planets 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.”
Back in 1226, Genghis Khan was taking over parts of Russia and the 5th Crusade was trying to capture land in Egypt.