Once-in-a-lifetime comet to be visible in Seattle starting Saturday

Stargazing Seattleites could get a once-in-800-centuries chance to see Comet Tsuchinshan-ATLAS on the horizon on Saturday — as long as the clouds cooperate.

People should be able to see the spectacle, known as Comet C/2023 A3, with the naked eye about 45 minutes after sunset Saturday, said Bill Cooke, who leads NASA’s Meteoroid Environment Office. The soaring “snowy dirtball,” Cooke said, will then be visible nightly until about Halloween. Earth will dodge it by about 44 million miles, according to NASA. It will appear progressively dimmer and higher in the sky until disappearing from view.

Luckily for amateur astronomers, clouds aren’t expected to block this weekend’s celestial sight in most of Western Washington, said National Weather Service meteorologist Kayla Mazurkiewicz.

“We’ll generally have clear skies and a few high clouds, but it won’t be anything like right now,” she said, on a gloomy Tuesday.

The forecast, if it holds, will give Washingtonians the chance to greet the comet for the last time before it hurtles out of sight on its path around the sun for another 80,000 years, Cooke said.

“Bright comets are always spectacular, and this one will be the brightest comet since 2006,” Cook said. “It’s certainly worth a look.”

How can I see the comet?

Catching a glimpse of Comet Tsuchinshan-ATLAS is pretty simple, Cooke said: “Go outside about 45 minutes after sunset and look west.”

The comet should appear low on the western horizon “in the glow of the twilight,” he said. While the comet should be visible at first without special instruments, Cooke recommended using a pair of binoculars or a telescope.

Alan Spurgeon, president of the Seattle Astronomical Society, a 500-member group of amateur astronomers, also recommended going somewhere with an unobstructed view of the horizon, like a big open field or the top of a hill. People should also try to find someplace dark and cloudless, such as hiking trail at high elevation or in rural Eastern Washington, he said.

“If you can see the Olympics, then you’ve probably got a good view to the horizon,” Spurgeon said.

What is Comet Tsuchinshan-ATLAS?

Comets, including Tsuchinshan-ATLAS, are like “big clots of dirt a couple miles across mixed with ice and snow” flying through space, Cooke said. The entities orbit in what scientists call the Oort Cloud: a shell of billions upon billions of comets surrounding the solar system, he said.

About every couple of years, the gravity of passing stars tugs a comet into the solar system, bringing it close enough to Earth for humans to see with the naked eye, Cooke said.

Observers in China and South Africa first spotted and identified Comet Tsuchinshan-ATLAS last year. About two weeks ago, the comet survived flying past the sun, keeping it on track to pass Earth before sailing back into the cosmos, according to NASA.