The Great Conjunction
December 21, 2020
Sky watchers received a treat last night for sure!
What has become known popularly as the “Christmas Star” is an especially vibrant planetary conjunction easily visible in the evening sky over the next two weeks as the bright planets Jupiter and Saturn come together, culminating last night (Dec. 21st).
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 the 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 planets regularly appear to pass each other in the solar system, with the positions of Jupiter and Saturn being aligned in the sky about once every 20 years.
What makes this year’s spectacle so rare?
It’s been almost 400 years since the planets passed this close to each other in the sky, and nearly 800 years since the alignment of Saturn and Jupiter occurred at night, as it will for 2020, allowing nearly everyone around the world to witness this “great conjunction.”
The closest alignment will appear just a tenth of a degree apart and last for a few days. Last night, they appeared so close that a pinkie finger at arm’s length could cover both planets in the sky. The planets will be easy to see with the unaided eye by looking toward the southwest just after sunset.
While the best viewing night has already occurred, those who would like to see this phenomenon for themselves still have a chance to view it on December 22nd but slightly shifted:
- Find a spot with an unobstructed view of the sky, such as a field or park. Jupiter and Saturn are bright, so they can be seen even from most cities.
- An hour after sunset, look to the southwestern sky. Jupiter will look like a bright star and be easily visible. Saturn will be slightly fainter and will appear slightly above and to the left of Jupiter until December 21, when Jupiter will overtake it and they will reverse positions in the sky.
- The planets can be seen with the unaided eye, but if you have binoculars or a small telescope, you may be able to see Jupiter’s four large moons orbiting the giant planet.
Enjoy and happy star gazing!
