Earthlings treated to rare alignment of Jupiter and Saturn

The evening sky over the northern hemisphere treated stargazers to a once-in-a-lifetime illusion on Monday as the solar system's two biggest planets appeared to meet in a celestial alignment that astronomers call the "Great Conjunction."

The rare spectacle resulted from a near convergence of the orbits of Jupiter and Saturn that happened to coincide with Monday's winter solstice, the shortest day of the entire year. For those able to take notice of the alignment in clear skies, both frozen-gas spheres appeared closer and more vibrant - almost as an individual point of light - than anytime in 800 years.

Jupiter - the brighter and larger of the pair - has been steadily nearing Saturn in the sky for weeks as both planets proceed around the sun, each in its lane of a massive celestial racetrack, said Henry Throop, an astronomer at National Aeronautics and Space Administration headquarters in Washington.

"From our vantage point, we’ll have the ability to be to see Jupiter inside lane, approaching Saturn all month and lastly overtaking it on Dec 21,” Throop said in a statement the other day.

At the point of convergence, Jupiter and Saturn were just one-tenth of a degree apart, roughly equivalent to the thickness of a dime held at arm's length. The truth is, of course, the planets remained vast sums of miles apart, according to NASA.

A conjunction of both planets takes place about once every twenty years. But the last time Jupiter and Saturn came as close together in the sky as on Monday was in 1623, an alignment that occurred during daylight and was thus not obvious from most places on Earth.

The last obvious great conjunction occurred long before telescopes were invented, in 1226, halfway through construction of the Notre Dame cathedral in Paris.

The heightened brightness of both planets because they almost merge in the sky has invited the inevitable speculation about whether they formed the "Christmas star" that the brand new Testament describes as having guided the three wise men to the baby Jesus.

But astronomer Billy Teets, acting director of Vanderbilt University’s Dyer Observatory in Brentwood, Tennessee, said an excellent Conjunction is only one of the possible explanations for the biblical phenomenon.

"I think that you will find a lot of debate in regards to what that might have already been,” Teets told WKRN-TV in Nashville in a recently available interview.

Astronomers suggested that the best way to view Monday's conjunction was by looking toward the southwest within an open area about one hour after sunset.

"Big telescopes don't help that much, modest binoculars are perfect, and even the eyeball is okay for since they are right together,” Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics, wrote in an email to Reuters.

Another Great Conjunction between your two planets - though not almost as close together - will come in November 2040. A closer alignment similar to Monday’s will maintain March 2080, McDowell said, with the next close conjunction 337 years later in August 2417.