Jupiter and Saturn will merge in the night sky on Monday, appearing closer to one another than they have since the 17th century.
The phenomenon, referred to as ‘The Great Conjunction’ is a rare astronomic event that will occur tonight. Saturn and Jupiter, the two largest planets in our solar system, will nearly overlap to form a “double planet,” an event that hasn’t been visible since the Middle Ages. December 21, also marks the winter solstice in the Northern Hemisphere, the longest night of the year and the summer solstice in the Southern Hemisphere.
Astronomers say so-called conjunctions between the two planets aren’t particularly rare. But the one coming up 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.
“What is most rare is a close conjunction that occurs in our nighttime sky,” said Vanderbilt University’s David Weintraub, an astronomy professor. “I think it’s fair to say that such an event typically may occur just once in any one person’s lifetime, and I think ‘once in my lifetime’ is a pretty good test of whether something merits being labeled as rare or special.”
It will be the closest Jupiter-Saturn pairing since July 1623, when the two planets appeared a little nearer.
To see it, watchers should be ready shortly after sunset Monday, looking to the southwest fairly low on the horizon. Saturn will be the smaller, fainter blob at Jupiter’s upper right. Binoculars will be needed to separate the two planets.
Despite appearances, Jupiter and Saturn will actually be more than 450 million miles (730 million kilometers) apart. Earth, meanwhile, will be 550 million miles (890 million kilometers) from Jupiter.
A telescope will not only capture Jupiter and Saturn in the same field of view, but even some of their brightest moons.
Their next super-close pairing is in sixty years on March 15, 2080.