Tonight, Jupiter and Saturn will merge in the night sky, appearing closer to one another than they have since Galileo's time in the 17th century.
Jupiter passes its neighbour Saturn in their respective laps around the sun every 20 years. But the one coming up later tonight is especially close. Jupiter and Saturn will be just one-tenth of a degree apart from our perspective or about one-fifth the width of a full moon. They should be easily visible around the world a little after sunset, depending on the weather conditions, according to a PTI report.
Toss in the winter solstice in the Northern Hemisphere, the longest night of the year — and the summer solstice in the Southern Hemisphere — and this just-in-time-for-Christmas spectacle promises to be one of the greatest of Great Conjunctions.
This will be the closest Jupiter-Saturn pairing since July 1623, when the two planets appeared a little nearer. This conjunction was almost impossible to see, however, because of its closeness to the sun. Considerably closer and in plain view was the March 1226 conjunction of the two planets — when Genghis Khan was conquering Asia. Monday night's conjunction will be the closest pairing that is visible since way back then.
“Conjunctions like this could happen on any day of the year, depending on where the planets are in their orbits,” said Henry Throop, astronomer in the Planetary Science Division at the Nasa Headquarters in Washington, in an official release earlier this month. “The date of the conjunction is determined by the positions of Jupiter, Saturn, and the Earth in their paths around the Sun, while the date of the solstice is determined by the tilt of Earth’s axis. The solstice is the longest night of the year, so this rare coincidence will give people a great chance to go outside and see the solar system,” Throop adds.
Saturn and Jupiter have been drawing closer in the south-southwest sky for weeks. Jupiter — which is bigger and closer to Earth — is vastly brighter. Saturn will be the smaller, fainter blob at Jupiter's upper right. Despite appearances, Jupiter and Saturn will actually be more than 450 million miles (730 million km) apart. Earth, meanwhile, will be 550 million miles (890 million km) from Jupiter. According to an AP report, their next super-close pairing will be on March 15, 2080, which makes this pretty much a once-in-a-lifetime celestial event for many.
If you want to spot this phenomenon, here’s what Nasa suggests you do:
- 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.