Astronomers use the term conjunction to describe meetings of planets and other objects on our sky’s dome. They use the term great conjunction to describe meetings of the two biggest worlds in our solar system, Jupiter and Saturn.
This year, on the night of December 21, stargazers will be in for a holiday treat and a chance to see a Christmas “kiss” beneath interplanetary mistletoe when Jupiter and Saturn will appear closer to one another and brighter than they have since middle age in an event known as a “great conjunction”.
According to NASA,
In 1610, Italian astronomer Galileo Galilei pointed his telescope to the night sky, discovering the four moons of Jupiter – Io, Europa, Ganymede, and Callisto. In that same year, Galileo also discovered a strange oval surrounding Saturn, which later observations determined to be its rings. These discoveries changed how people understood the far reaches of our solar system.
Thirteen years later, in 1623, the solar system’s two giant planets, Jupiter and Saturn, traveled together across the sky. Jupiter caught up to and passed Saturn, in an astronomical event known as a “Great Conjunction.”
The world will see a planetary phenomenon that hasn’t occurred in 800 years. On that night, Jupiter, the largest planet in our solar system, and ringed Saturn, the second-largest, will line up perfectly to look like a double planet in the night sky.
The two planets will be so close that they will appear to be touching, separated by one-fifth the diameter of a full moon. It will be the closest they’ve appeared since March 4, 1226. “The two planets have been brilliant highlights of the night sky for much of this year, and are now getting closer together in advance of their super close pairing in mid-December,” NASA said. “Be sure to watch as they draw a little nearer to each other each week.”
When celestial bodies align, it’s called a conjunction, but since this one involves our solar system’s two biggest gas giants, it’s known as the “great conjunction.” Though the two planets will look close together, they actually will be more than four times the distance between Earth and the sun.