Jupiter and Saturn unite to form ‘Christmas star’ in brightest conjunction in 800 years
After all that 2020 and its clarified vision have shown us, this most epic of years has one more thing up its sleeve – a light bright enough to put Earthly concerns into perspective – and coinciding with the first day of winter, to boot.
For the past few weeks, mighty Jupiter and Saturn – the gas giants, and the biggest planets in our solar system – have been edging closer and closer together, at least from Earthlings’ vantage point.
At some point every 20 years or so, they appear to converge in the sky, a happening known as a conjunction. Starting Friday, we can see the two planets on the home stretch by looking southwest starting about 30 minutes after sunset each night. The visage will be evident to the naked eye, but those with a telescope will be able to see the planets’ moons arrayed on either side, NASA says.
This year, the event promises to be so stunning that astronomers call it a “great conjunction.” The planets have not appeared this close together, or this bright, in 800 years. The two planets have not passed this close to one another in 400 years, since 1623, and the last time they aligned at night was in 1226, NASA explains. (They are, of course, millions of miles apart.)
And it will happen on the evening of the winter solstice, which is Monday.
Between now and then, as Earthsky.org notes, we can see the two getting closer and closer together, shimmering alongside a widening crescent moon, hovering over the horizon soon after sunset. Jupiter is brighter than the stars, and Saturn is their equal, though golden in color. Unlike stars, which twinkle, the planets shine steadily.
Most of us missed the last conjunction, in 2000, because the two planets were too close to the sun to be easily observed. But now the two are rising every evening just after sunset, “easily visible and exceedingly noticeable,” Earthsky says.
Starting Friday night, the two planets will appear just a moon’s width apart, with the actual crescent moon just below them, Astronomy magazine notes. The trio will appear low in the southwest about a half hour after sunset. Moreover, “the shadowed portion of the Moon is illuminated by earthshine, making the whole satellite visible against the deepening twilight,” Astronomy says. “The moon sets shortly after 7:20 p.m. local time, and the planets follow 20 minutes later.”
And that’s just the prelude.
Jupiter takes 12 Earth years to orbit the sun, and Saturn does so every 29.5 years. Planetary conjunctions are possible because they all lie in approximately the same plane, Sky and Telescope explains, not unlike runners on concentric tracks. When two or more planets arrive at the same point on their orbital path in relation to Earth’s vantage point, they can appear as one. That is what’s happening on Monday night.
“You can imagine the solar system to be a racetrack, with each of the planets as a runner in their own lane and the Earth toward the center of the stadium,” NASA astronomer Henry Throop said in a statement. “From our vantage point, we’ll be able to be to see Jupiter on the inside lane, approaching Saturn all month and finally overtaking it on December 21.”
Its proximity time-wise to Christmas will inevitably evoke images of and comparisons to the fabled Star of Bethlehem.
Jupiter and Saturn won’t even become close to being this close again till 2080, says Earthsky, making this a potential once-in-a-lifetime vista, as well as a once-in-a-millennia phenom.
