This week there will be a rare object in the sky over Colorado. 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 of each other in early 2023.

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

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 become. The good news is that because the comet came from the depths of space before orbiting the sun, it was visible in the southern hemisphere. And our colleagues in the south have said that the view is amazing: a big long tail, a very, very impressive comet. So unless the comet melted too much or broke up as it orbited the sun, we expect it to have a beautiful tail stretching across the sky as it appears in the northern sky in the coming evenings.

The biggest thing getting in the way of a good view of this comet is probably not the comet itself. They are your neighborhood lights. If you want a good view of the comet, you should stay away from the lights. Number two: because it is so close to the sun, it is visible right after sunset. It’s not far up there where the sun sets, so you don’t want to be blocked by the mountains. If you live near 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’m only going to drive 15 minutes and I expect to see a beautiful long comet tail.

Michelle Fulcher: Am I looking north? South?

Duncan: It will be exactly where the sun has set and this time of year the sun sets almost exactly in the west. So if you look west, you expect to see the comet’s tail, which is always pointing away from the Sun and sticking up, right where the Sun set 15 minutes or half an hour earlier. Don’t confuse a comet with a meteor. They both have tails, but within a few seconds a meteor shoots through 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 the distance from the Earth to the Sun. So it’s not very close. On the other hand, compared to where it came from, it has gotten closer and closer. That’s why it’s so beneficial to see it this week.

Fulcher: Where does it come from?

Duncan: When we measure the comet’s orbit, believe it or not, it came from a thousand times farther away than Pluto. We think that far out in space, much of the way to the nearby stars, but still associated with the Sun, is a large cloud called the Oort Cloud. So apparently far out there, far beyond Pluto, there is a cloud of comets. If something disturbs them and changes their orbit, they can get close to the sun, close to the Earth. And that is what has happened now.

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

Duncan: We don’t know what the best night or nights will be to see the comet.

You see, every night it gets further away from the sun, and it gets a little dimmer. However, it is located higher in the sky. This means that you can look at the comet when the sky is nice and dark. By far the best view of a comet is when the sky behind the comet is black. If the sky is still dim and a bit gray, or there is light pollution from the city, you may be able to see the comet, but it won’t be as spectacular. So I think it’s entirely possible that the best nights will happen late this weekend or early next week.

Fulcher: People want to take pictures of everything these days, but this sounds like it’s hard to do.

Duncan: I have very good news. Modern smartphones – I have an iPhone 14 Pro Max, something like that, something like a Pixel or an Android phone that’s quite modern, they all have a night mode. They actually take a time exposure. They typically have three seconds in which they collect light and they create a brighter image than even your eyes can see. So if you have such a phone, take it with you. Make sure it’s in night mode, keep it as steady as possible and you might get a spectacular photo of this comet.