There will be a rare object in the skies over Colorado this week. Comet Tsuchinshan-ATLAS will be visible just above the western horizon shortly after sunset.

Astronomers say the comet was last visible from Earth about 80,000 years ago, when Neanderthals roamed the planet. Scientists in China and South Africa discovered it within about a month in early 2023.

Astronomer Doug Duncan, former director of the Fiske Planetarium at the University of Colorado Boulder, spoke with Michelle P. Fulcher, executive producer of Colorado Matters.

Editor's Note: This interview transcript has been edited for length and clarity.

Doug Duncan: The professional astronomers watched it get closer and closer to the Sun and Earth to see how bright it would get. The good news is that before the comet orbited the Sun, it came from deep space and was visible in the Southern Hemisphere. And our colleagues down south said the view was great – a big long tail, a very, very impressive comet. So unless the comet melted too much or disintegrated as it orbited the sun, we expect that when it appears in the northern sky in the next few evenings it will have a beautiful tail stretching across the sky.

The biggest obstacle to getting a good view of this comet probably isn't the comet itself. It's your neighborhood lights. If you want a good view of the comet, you'll need to stay away from the lights. Second, because it is so close to the sun, it is visible right after sunset. It's not very far above where the sun sets, so you don't want to be blocked by the mountains. If you live right next to the Rocky Mountains and don't see where the sun sets, you won't see the comet. Where I live in Boulder there is a beautiful, convenient mountain called Flagstaff, and I only drive 15 minutes and expect to see a beautiful long tail of a comet.

Michelle Fulcher: Am I facing north? South?

Duncan: It will be right where the sun set, and this time of year the sun sets almost exactly to the west. So if you look west, expect to see the comet's tail, always pointing away from the sun, reaching into the sky exactly where the sun set 15 minutes or half an hour earlier. Don't confuse a comet with a meteor. They both have tails, but in a few seconds a meteor races across the sky. A comet will remain in the sky for many days or even weeks.

Fulcher: How far is the comet from Earth?

Duncan: It is approximately equal to the Earth's distance from the Sun. So it's not very close. On the other hand, it has gotten closer and closer compared to its place of origin. That's why it's such a good time to see it this week.

Fulcher: Where does it come from?

Duncan: If you measure the comet's orbit, believe it or not, it comes a thousand times further away than Pluto. We think that far out in space, a good part of the way to the nearby stars but still connected to the Sun, there is a large cloud called the Oort Cloud. So apparently there is a cloud of comets far out there, far behind Pluto. If something disturbs them and changes their orbit, they can come close to the Sun and Earth. And that's exactly what happened now.

Fulcher: So it will be visible this weekend. What are probably the best days?

Duncan: We don't know which night or nights will be the best for observing the comet.

You see, every night it moves further away from the sun and becomes a little dimmer. However, it is higher in the sky. This means you can view the comet when the sky is nice and dark. By far the most beautiful view of a comet is when the sky behind the comet is black. If the sky is still twilight and a bit gray, or if there is light pollution in the city, you may be able to see the comet, but it will not be as spectacular. So I think it's entirely possible that the best nights will happen at the end of the weekend or early next week.

Fulcher: Nowadays you want to photograph everything, but it seems difficult.

Duncan: I have really good news. Modern smartphones – I have an iPhone 14 Pro Max, something like that, something like a Pixel or an Android phone that's pretty modern, they all have night mode. You're actually taking a long exposure. They typically have three seconds to collect light, and they produce a brighter image than even your eyes can see. So if you have a phone like this, bring it with you. Make sure night mode is turned on, keep it as still as possible, then you might get a spectacular image of this comet.