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As Comet C/2023 A3 (Tsuchinshan–ATLAS) barrels its way through space, some have gotten a view of the object that’s so nice, it appears to have sprouted a tail, twice.
The comet, discovered in January 2023, reached its perihelion—the point in its orbit where it’s closest to the Sun—on September 27. Its path then sent it on a trajectory where it reached its closest point to Earth on October 12. It takes A3 an estimated 80,000 years to complete a single orbit of the Sun, a period so long that, the last time it was in this part of its orbit, Neanderthals still roamed the Earth, long before telescopes were even invented.
According to EarthSky, this comet (known colloquially as Comet A3, for obvious reasons) is special, as it’s the brightest to cross our planet’s sky in 27 years, leading some to dub it the Comet of the Century. Accordingly, it’s a big deal, and this big deal has just sprouted a rare “anti-tail.”
This is an absolutely amazing simulation of the behavior of Comet C/2023 A3 (Tsuchinshan-ATLAS) by @nlefaudeux 🤩 #Comet #Astronomy #TsuchinshanATLAS #Cometa #CometC2023A3 #Tsuchinshan #C2023A3 #FollowTheComet pic.twitter.com/lpAWezXzp4
— Yuri Beletsky (@YBeletsky) September 27, 2024
What astronomers hadn’t anticipated was a quirk of gravity, light, and physics that makes the comet appear to have a typical tail trailing behind it in some views, while in others, it seemed to shoot out from the front.
Comet A3’s tail, like that of all comets, is composed of dust and gas blowing off as the object heats up as it passes close to the Sun. The front tail, known as an anti-tail, is made up of some of the same stuff, and is something of an optical illusion. As the dust gets knocked off the comet, some of it remains in the parent body’s orbital plane. As the Earth passes through that plane, the debris reflects sunlight, giving those of us on the planet the appearance of a second tail, according to EarthSky.
Comet A3 with anti-tail. Image: Stephen Kwong The quirk has appeared in several photographs, perhaps most prominently in one taken by astrophotographer Michael Jäger, who sent the snap to LiveScience. The anti-tail can also be seen in photos and videos posted to social media.
Comet C/2023 A3 (Tsuchinshan-ATLAS) is finally properly visible from the Netherlands, and putting on quite a show.#comet #komeet #CometC2023A3 pic.twitter.com/gISUinSo1P
— Gijs de Reijke (@GijsDeReijke) October 15, 2024
Despite now moving away from the Earth, Comet A3 is still visible in the sky (the comet currently appears along the western horizon at sunrise), even without a telescope or binoculars, but it won’t be for long. By the end of the month, it will have moved out of range. If your nights are packed for the next two weeks, and you won’t get a chance to get a look, you might want to start berating yourself a little. It will only take Tsuchinshan-ATLAS another 80,000 years to come this close to Earth again, so unless you’re big into cryogenics, you probably aren’t going to get another chance.
