When Jupiter and Saturn appear close together in the night sky this week, their combined light might be what the Bible’s nativity story in the Gospel of Matthew called the Star of Bethlehem, according to faculty and staff at Ball State University.
“People have long wondered if the Star of Bethlehem could be explained by natural celestial events. Some astronomers believe the ‘star’ may have been a series of celestial events,” said Dayna Thompson, director of the Charles W. Brown Planetarium at Ball State.
In coming days, Jupiter and Saturn will appear closer in the sky then they have in 400 years. This event has been labeled “The Great Conjunction,” Thompson said.
Such events have been recorded for thousands of years, she noted.
“For ancient people, the word ‘star’ didn’t have the same meaning that it does for us today,” she said. “Sometimes comets were referred to as stars. Also, ‘star’ didn’t have to refer to a single celestial object or event.”
Jupiter and Saturn appeared close together in the sky in the years 7, 6, and 5 BC in a constellation astrologically significant to the Jewish people. This was followed by the appearance of an exploding star in the pre-dawn sky of 5 BC. These events are all candidates for natural occurrences of the Star of Bethlehem, Thompson said.
“This is one reason why people are referring to the current close grouping of Jupiter and Saturn starting on December 21 as a ‘Christmas Star’ event,” she said. “The other reason, of course being the date of the event, as it’s so close to Christmas. December 21 also happens to be the date of the Winter Solstice – the shortest day of the year.”
An astronomical conjunction occurs when any two heavenly bodies appear to pass or meet each other as seen from Earth. To make one “great,” though, requires an encounter between our solar system’s two largest planets. The orbits of Jupiter and Saturn align to allow the giant worlds to seemingly convene roughly every 20 years.
While called a Great Conjunction, of course, the planets are never actually close at all; during this week’s encounter, they will still be separated by more than 453 million miles.
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For the last great conjunction, on May 28, 2000, the apparent distance between Jupiter and Saturn in the sky was 68.9 arc minutes, or more than twice the diameter of the full moon. The 2020’s great conjunction coincides with the December solsticeand appear roughly the thickness of a dime held at arm’s length.
The last time Jupiter and Saturn appeared so close was July 16, 1623, when Galileo was still alive, a little more than a decade after he first used a telescope to discover Jupiter’s four largest moons that now collectively bear his name. The odds are low, however, that Galileo or anyone else on Earth managed to witness that great conjunction, which was virtually impossible to see because of its apparent position near the sun.
The prior great conjunction to appear as close and as visible as the current one occurred on March 4, 1226. “For perspective, Genghis Khan was still roaming Asia then,” says astronomer Patrick Hartigan at Rice University in Houston.
To view the current Great Conjunction, find a spot where you can watch the sunset with a clear horizon in front of you, free of trees or buildings. In the hour or so after nightfall, first Jupiter will appear in the western sky, and then Saturn, both shining dots distinguishable from the stars by the fact they do not twinkle.
Although the great conjunction arrived on Monday, Dec. 21, “while fading, Jupiter and Saturn will still be visble through Christmas. By watching, you can get a sense how celestial mechanics works in the nighttime sky.
The BSU planetarium’s “Christmas Star” program explores potential natural explanations for the Star of Bethlehem and common modern-day misconceptions about the event, researched and written by Dr. Ron Kaitchuck, the previous director of the Brown Planetarium and professor emeritus.
While the planetarium is closed this holiday season due to COVID-19, its “Christmas Star” planetarium program is on YouTube 360 at https://youtu.be/Wq_1CwKbkaY
