Last Chance For 80,000 Years To See Comet As It Gets Closest To Earth

The brightest comet for over 10 years will be visible to the naked eye this weekend from the northern hemisphere as it makes its once-in-80,000 years journey around the sun.

First discovered in January 2023 by the Tsuchinshan (Purple Mountain) Astronomical Observatory in China, Comet Tsuchinshan-ATLAS — also called comet A3 and C/2023 A3 (Tsuchinshan-ATLAS) — will today get to within 44 million miles (70 million kilometers) of Earth, the closest it will get.

What Is Comet A3 (Tsuchinshan-ATLAS)?

It's a large, long-period comet from the Oort Cloud, a sphere of millions of comets wrapped around the solar system. It has a coma about 130,000 miles (209,000 kilometers) in diameter and a tail that streams about 18 million miles (29 million km) away from the sun into the solar system, according to Space.com.

Observers should not need binoculars to see the comet, but they will enhance the view. Here's everything you need to know about seeing Comet Tsuchinshan-ATLAS with your naked eyes this weekend and beyond.

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Where To See Comet A3 (Tsuchinshan-ATLAS)

Comet Tsuchinshan-ATLAS is currently exiting from the sun's glare and is positioned due west just after sunset. As such, it's both low on the brightest part of the horizon and sinks below it during twilight.

To see it, find out the exact time of sunset where you are and be in position 30 minutes after that. You need to look west just above where the sun has recently set. You'll need somewhere you can see low to the western horizon. If you have a place local to you where you like to watch sunsets, that's ideal.

It will be positioned between Antares, the brightest star in the constellation Scorpius, and Arcturus, the brightest star in the constellation Boötes, according to Sky & Telescope.

When To See Comet A3 (Tsuchinshan-ATLAS)

Act quickly because this comet will not be bright for long. "It should start to become clearly visible around the evening of Oct. 12 and very prominent on Oct. 13 and Oct. 14 when it will have a bright downward spike in addition to its normal upward pointing tail," said Dr. Qicheng Zhang, an astronomer at Lowell Observatory in Flagstaff, Arizona, who has been monitoring the comet, in an email.

Over the next few days, it will climb higher into the post-sunset sky. As it does, it should appear brighter because it will be set against a slightly darker sky and take longer to set.

Why You Need To See Comet A3 (Tsuchinshan-ATLAS) Soon

Comet Tsuchinshan-ATLAS is already fading. That's a consequence of the timing and position of the comet in Earth's sky, which is far from ideal. Technically speaking, the comet reached its brightest on Oct. 9 when it reached magnitude -4 (as bright as Venus) while lost in the sun's glare. As it did, it became visible to NASA's SOHO Observatory, which permanently monitors the sun. At that point, it was the brightest comet in over a decade.

"It's now fading, but also becoming much easier to see and more visually prominent in the evening as it moves away from the sun," said Zhang. "It should stay fairly prominent over the next few days as the fading comet is balanced out by the darker sky as it moves away from the sun until about Oct. 19 or 20."

Wishing you clear skies and wide eyes.