NEW YORK – The evening sky over the Northern Hemisphere treated stargazers Monday for a once-in-a-lifetime illusion, when the solar system’s two largest planets appeared to meet in a celestial alignment that astronomers call the “Great Conjunction.”
The rare spectacle was the result of a near coincidence of the orbits of Jupiter and Saturn that happened to coincide with Monday’s winter solstice, the shortest day of the year.
To those who could observe the alignment in a clear sky, the two frozen gas spheres seemed closer and more vibrant – almost like a single point of light – than at any time in 800 years.
Jupiter – the brightest and larger of the pair – has been gradually approaching Saturn in the sky for weeks as the two planets orbit the sun, each in their own orbits of a massive celestial circuit, said Henry Throop, an astronomer with National Aeronautics and Space Administration headquarters in Washington.
“From our vantage point, we will be able to see Jupiter on the inner orbit, approach Saturn for the entire month and finally catch up on December 21,” Throop said in a statement last week.
At the point of meeting, Jupiter and Saturn appeared to be only one-tenth of a degree apart, roughly equal to the thickness of a dime at an arm’s length. In reality, the planets were, of course, hundreds of millions of miles apart, according to NASA.
A conjunction of the two planets takes place about once every 20 years. But the last time Jupiter and Saturn came so close to each other in the sky as on Monday was in 1623, an alignment that occurred in daylight and so was not visible from most places on Earth.
The last visible great conjunction occurred long before telescopes were invented, in 1226, halfway through the construction of Notre Dame Cathedral in Paris.
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The increased brightness of the two planets, while almost merging in the sky, has given rise to speculation as to whether they formed the “poinsettia” that the New Testament describes as leading the three wise men to the baby Jesus.
But astronomer Billy Teets, acting director of the Dyer Observatory at Vanderbilt University in Brentwood, Tennessee, said a Great Conjunction is just one of many possible explanations for the biblical phenomenon.
“I think there is a lot of debate about what that could be,” Teets told WKRN-TV in Nashville in a recent interview.
Astronomers suggested that the best way to view Monday’s conjunction was to look southwest in open space about an hour after sunset.
“Big telescopes don’t help much, modest binoculars are perfect, and even the eyeball is okay to see they match,” Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics, told Reuters by email. .
The next Great Conjunction between the two planets – although not nearly as close together – will come in November 2040.
A closer alignment, similar to Monday, will take place in March 2080, McDowell said, with the next close conjunction 337 years later, in August 2417.