An ancient comet not seen for 80,000 years is visible in Colorado’s night sky. Here’s how to spot it.

Coloradans looking to the west in the early evening hours this week have the chance of spotting an ancient marvel not seen for 80,000 years. 

An Oort Cloud comet is currently passing Earth as part of its highly elliptical trip around the solar system. It was identified in 2023 by observers at China’s Tsuchinshan Observatory and an ATLAS telescope in South Africa — with the comet being named Tsuchinshan-ATLAS. 

Scientists initially believed the comet — a large, frozen mass of space debris that includes dust, rocks and ice — would potentially break apart as it came closer to the intense heat of the sun. But it survived intact and came within 44 million miles of Earth late last week, according to the National Aeronautics and Space Administration. 

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“Comets are more fragile than people may realize,” said NASA astronomer Bill Cooke in a Oct. 2 blog post. “Comet Kohoutek, which reached the inner solar system in 1973, broke up while passing too close to the sun. Comet Ison similarly failed to survive the sun’s intense heat and gravity … in 2013.”

The rare occurrence provides an opportunity to view an astronomical object that originated along the very fringes of the solar system some 1 to 2 light years away. While the comet had been mostly visible in the Southern Hemisphere earlier this month, experts say now is prime viewing time for those on the other side of the equator. 

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“This is the week for people to really have a chance to see it with their naked eye and a pair of binoculars,” said Shawn Dahl, service coordinator for the National Weather Service’s Space Weather Prediction Center. 

At less than 50 million miles away, the comet is “pretty close” to Earth “and that’s why it’s so bright in the night sky,” Dahl said. 

The tail — estimated to be 18 million miles long — takes up around 10 degrees or more of the sky, with the horizon line being 0 degrees and directly above being 90. 

To see the comet, Dahl said to look to the west, with the object currently positioned between Venus and the bright star Arcturus. Currently, the best viewing window is between 7 and 8 p.m. when the comet is higher in the sky. As the night goes on, the comet will become closer to the horizon line which will make it more difficult to see. 

With each day that passes, the comet will become dimmer, but it will also move higher in the sky, meaning the optimal viewing window will shift later and later into the night. 

While the comet’s head, or nucleus, will likely be bright enough to be seen even in areas with light pollution, viewers may need to be in darker environments to make out its tail. Dahl recommended avoiding looking at phone screens before trying to find the comet with the naked eye “because that brightness will affect your eyes.” 

Still, the comet will likely appear brighter in photos, similar to the aurora borealis. Dahl, who is also an astrophotographer, said a long exposure shot on a phone will do the trick. 

If using a professional camera, Dahl recommends using the “500 rule,” which means dividing 500 by the focal length of the lens, to find the right exposure time. A 50 millimeter lens, for example, should shoot with a 10-second-long exposure. 

It’s unlikely the comet will be visible during the daytime. In the past 300 years of astronomical observation, only nine previous comets have been bright enough to spot during the day. The most recent were Comet West in 1976 and, under ideal conditions, Comet Hale-Bopp in 1997, according to NASA. 

In the best conditions, Comet Tsuchinshan-ATLAS could have similar brightness to Venus but won’t shine as intensely as Sirius, the brightest visible star in the night sky. By early November, the comet will be lost to the unaided eye. It’s possible the comet’s path may take it out of the solar system altogether, the agency stated.

Dahl said to savor the moment. 

“It will continue to get dimmer every day — it’s moving very quickly,” Dahl said. “It’s going to be a thing to behold right now and experience something that people won’t be able to see again in their lifetime.”