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The Christmas Star: Close encounters of the planetary kind

Last updated December 15, 2020

By Tina Underwood

Physics Professor and Department Chair David Moffett knows exactly where he’ll be Monday, Dec. 21, around sunset – behind a telescope trained on the southwestern sky. That’s when he and countless others will observe something that hasn’t been seen in the night sky in nearly 800 years – the “Christmas Star.”

Saturn and Jupiter above the PAC

A recent photo of Saturn and Jupiter as seen above the PAC. Photo/David Moffett

But it’s not a star. It’s a conjunction, which occurs when two or more bright objects come so close together, that to the unaided eye, they appear as one, explains Moffett.

This celestial pas de duex happens with behemoths Jupiter and Saturn this year, coincidentally, on the Winter Solstice. A conjunction of this kind occurs roughly every 20 years, but the two gas giants haven’t been this close in centuries – not since 1226, Moffett says.

Their orbits will come within one-tenth of a degree of one another, still hundreds of millions of miles apart. And because of the conjunction’s close proximity to the Christmas holiday, it’s been dubbed the Christmas Star. But that’s not the only reason for the label.

Some say the Biblical account of the star that appeared near the time of the birth of Christ could have been a conjunction like the one we’ll see. But it’s a hotly debated topic, Moffett says, because of the interdisciplinary nature of the mystery.

“You have theologians, historians and astronomers all trying to come together to solve what might have been the Christmas Star.”

He says the star that led the wise men to the Christ child could have been one of many different phenomena like a rare conjunction of Venus and Jupiter, or an occultation – when, for example, a moon crosses paths with a planet, or it could have been a conjunction of Jupiter and the star Regulus.

“We can’t discount that it might have been a comet,” says Moffett. “Halley’s Comet appeared in the year 12 BCE and another appeared in the year 5 BCE.” Still other possibilities would be a nova – “a star that appears out of nowhere,” he says, or a supernova, a powerful stellar explosion.

Add timing issues, people in positions of power at the time of the alleged Christmas or Bethlehem Star, and it “goes on and on,” Moffett says, so much so, in fact, that entire books and conferences were devoted to the topic in the past.

Regardless of what may have been witnessed by shepherds and wise men more than 2,000 years ago, what we know is that come Dec. 21 shortly after sunset, Jupiter and Saturn will put on quite the show beyond the moonless stratosphere, if clear skies prevail.

Moffett says to get the best view, “don’t tarry too long” past sunset (5:21 p.m. in Greenville) because the show is fleeting. His favorite place on campus (closed to the public due to COVID-19) is the road leading from the Lay Physical Activities Center to Cherrydale Alumni House. The hillside to the right as you pass the PAC provides a wide and unobstructed view of the western sky.

A frequent contributor to the neighborhood information platform, Nextdoor, Moffett is encouraging his community to get outdoors for the post-twilight drama, as it won’t happen again until 2080.

He also sees it as a fitting conclusion to 2020.

“For me, the Christmas Star always represented hope and new beginnings – it represented good news,” he says. “I think we deserve some good news at the end of this year.”

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