NEW YORK – The evening sky over the northern hemisphere treated stargazers with a once-in-a-lifetime illusion, as the two largest planets in the solar system appeared to meet in a celestial alignment that astronomers call the “Great Conjunction.”
The rare spectacle resulted from a close convergence of the orbits of Jupiter and Saturn that coincided with the winter solstice on Monday, the shortest day of the year.
For those able to observe alignment in the clear sky, the two spheres with frozen gas have appeared closer and more vibrant – almost like a single point of light – than ever before in 800 years.
Jupiter – the brightest and largest of the pairs – is gradually approaching Saturn in the sky for weeks, as the two planets continue around the sun, each on its own band of a huge celestial racetrack, said Henry Throop, an astronomer at National Aeronautics and Washington Space Administration Headquarters.
“From our point of view, we will be able to see Jupiter in the inner band, approaching Saturn all month and finally surpassing it on December 21,” Throop said in a statement last week.
At the point of convergence, Jupiter and Saturn seemed to be only a tenth of a degree, about the equivalent of the thickness of a penny held at arm’s length. In reality, of course, the planets are hundreds of millions of miles away, according to NASA.
A conjunction of the two planets takes place about once every 20 years. But the last time Jupiter and Saturn came as close to the sky as Monday was in 1623, an alignment that took place during the day and therefore was not visible from most places on Earth.
The last visible conjunction took place long before telescopes were invented, in 1226, in the middle of the construction of Notre Dame Cathedral in Paris.
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The increased brightness of the two planets, as they almost merge into the sky, has invited speculation as to whether they formed the “Christmas star” that the New Testament describes as guiding the three sages to the baby Jesus.
But astronomer Billy Teets, acting director of the Dyer Observatory at Vanderbilt University in Brentwood, Tennessee, said a large conjunction is just one of several possible explanations for the biblical phenomenon.
“I think there’s a lot of debate about what that could have been,” Teets told WKRN-TV in Nashville in a recent interview.
Astronomers have suggested that the best way to see Monday’s conjunction was to look southwest in an open area about an hour after sunset.
“Large telescopes don’t help that much, modest binoculars are perfect, and even the eyeball is fine to see that they’re right together,” Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics, told Reuters.
The next great conjunction between the two planets – though not nearly as close – comes in November 2040.
A closer alignment, similar to Monday, will be in March 2080, McDowell said, with the next tight conjunction 337 years later, in August 2417.