A once-in-a-lifetime holiday treat is on track to delight sky watchers later this month on the Winter Solstice. Jupiter and Saturn are moving closer to each other, culminating in a Great Conjunction on Dec. 21. You can watch the two large planets inch closer between now and the solstice.
Jupiter and Saturn have a conjunction every 20 years, so why is this time going to be so rare? It’s because of how cozy the two giant planets will appear. They will be so close, they will look like one big, bright star.
An observatory in Perth, Australia explained it this way:
“On the 21st of December, a once-in-a-lifetime opportunity will occur, #Jupiter and #Saturn will be in a Great Conjunction and will be so close, they’ll appear as a single bright star. The last time the two planets were this close was on the 16th of July 1623 while Galileo Galilei the father of observational astronomy was still alive.”
When Jupiter and Saturn snuggled up in 1623, that conjunction was likely not seen by very many people because it happened just 13 degrees east of the sun, closely following the sun at sunset, according to the experts at EarthSky. They go on to say:
“The closest observable Jupiter-Saturn conjunction before that was as long ago as during medieval times, in 1226! At their closest in December, Jupiter and Saturn will be only 0.1 degree apart. That’s just 1/5 of a full moon diameter. Start watching them now, and you’ll see them draw close together.”
If you miss this one, prepare for a long wait. The next close conjunction won’t happen until 2080.
The Great Conjunction happening later this month will mean both big planets will appear so close, people looking at them through a telescope will likely be able to see both in one field of view, according to NASA’s Jet Propulsion Laboratory in California. Here’s what else scientists there are telling sky watchers:
“Keep in mind that while the two gas giants may appear close, in reality they are hundreds of millions of miles apart. This will still be quite a striking sight, but you will need to look fast as both planets will set shortly after sunset. Look above the western horizon after sunset for these bright, close planets – a clear view will help!”
Because of the Dec. 21 timing, some people have dubbed this bright rarity “The Christmas Star.”
Gordon Johnston, the former planetary program executive at NASA who now pens a monthly blog about what’s going on in the solar system, suggests people start watching Jupiter and Saturn do their close dancing right around Dec. 16. Here are some excerpts from his latest blog:
Dec. 16: Jupiter and Saturn Near the Moon
“On Wednesday evening, December 16, the bright planet Jupiter and the fainter planet Saturn will appear near each other above the waxing crescent Moon. As evening twilight ends, the Moon will appear about 9 degrees above the southwestern horizon. Jupiter and Saturn will appear about 6 degrees above the Moon and quite near each other. The Moon will set first in the west-southwest.”
Dec. 17
“Thursday evening, December 17, 2020, will be the first of nine evenings when the bright planet Jupiter and the fainter planet Saturn will appear nearer to each other than the apparent diameter of the Moon (i.e., less than 1/2 of a degree apart). As evening twilight ends they will appear about 14 degrees above the southwestern horizon. The waxing crescent Moon will appear about 10 degrees above these planets. Each evening you can watch these planets shift closer to each other until they reach their closest on December 21, when they will be about 1/5 of the diameter of the Moon apart, after which they will gradually separate again. With a backyard telescope you should be able to see both of these planets in the same field of view (since most backyard telescopes easily view the full disk of the Moon).”
Dec. 21: Jupiter and Saturn Meet Up
“Monday evening, December 21, 2020, will be when the bright planet Jupiter and the fainter planet Saturn will appear nearest to each other, about 1/5 of the apparent diameter of the Moon (1/10 of a degree) apart. As evening twilight ends, they will appear about 12 degrees above the southwestern horizon.
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