Jupiter and Saturn will appear as the brightest stars in the sky this evening during an event that hasn’t been visible from Earth in this way for nearly 800 years.
Just after sunset, stargazers can look southwest of the horizon to see the two gas giants seemingly close together in the sky. The event, called a conjunction, is when celestial objects’ orbits around the sun seem to align.
“Jupiter will be reflecting the sunlight and appearing very bright in our night sky,” said Mike Hennessy, manager of the Buhl Planetarium at the Carnegie Science Center. “And then just up a little bit and to the left, you’ll see the planet Saturn glowing more faintly.”
Jupiter, the solar system’s largest planet, is 549 million miles from Earth; it takes about 29 Earth-years to orbit the sun. Saturn, known for its signature rings of dust and ice, is more than 1 billion miles from Earth; it takes about 12 years to orbit the sun.
“From our perspective on Earth, a conjunction of Jupiter and Saturn actually happens every 20 years,” Hennessy said. “But the orbits of the planet around the sun aren't exactly flat. They're all slightly tilted. So this is a rarity to see Jupiter pass this close to Saturn.”
The last time the conditions were right for viewing the conjunction of the two planets (not during the day when the sun was out) was in 1226. It’ll happen again, Hennessy said, in 2080.
If clouds obscure the night sky on Monday, Hennessy said the two planets will still appear close together for the next few days.
“Jupiter and Saturn are putting on a show throughout the holiday season,” Hennessy said. “It's a great sort of cosmic treat for us at the end of the year.”
The Carnegie Science Center will also hold a Facebook Live event for people to watch the conjunction together and talk with scientists.