Want to see Comet A3? It’s back! West after sunset

By Spacephototshirts
This illustration shows Comet C/2023 A3 (Tsuchinshan–ATLAS) – aka Comet A3 – around October 13-14. Illustration by Eddie Irizarry using Stellarium. The comet has been in the daytime sky for some days. But now it’s back in the evening sky! We had multiple reports last night, from people who saw it, from rural locations. Look for its long tail, a couple of fist-widths to the right of the brightest planet Venus – in the west shortly after sunset.

Look west after sunset for Comet A3

Comet C/2023 A3 (Tsuchinshan–ATLAS) put on a fantastic show in the morning sky for Southern Hemisphere observers with dark skies and good optical aid in September and early October. See amazing images of the comet here. Then A3 was lost in the sun’s glare for a few days. Now it’s back, quite low along the western horizon as soon as the sun disappears!

Every evening now, Comet A3 will appear a bit higher from the horizon in the hour or so after sunset. Its perihelion (closest point to the sun) was September 27. And its closest point to Earth was yesterday, October 12. So it’s now moving away from us, and thereby getting fainter. And yet – in the days ahead – it will be easier to see than it was for its morning appearance last month. That’s because many comets are brighter after perihelion. And it’s because the comet be farther each evening from the sun’s glare.

Here’s a chart, plus some images from people who caught it last night, on the day of the comet’s closest approach to Earth.

Star chart showing a comet with tail pointing away from the horizon for 2 dates, 1 closer to the horizon and 1 higher up.
If we are fortunate, the comet will grace our sky from October 14 to 24. Look to the west shortly after sunset for Comet Tsuchinshan–ATLAS. Chart by John Jardine Goss/ EarthSky.
City lights with a comet in the sunset sky above.
View at EarthSky Community Photos. | Teresa Molinaro in Sicily, Italy, captured Comet A3 on October 12, 2024. Teresa wrote: “On the day of its passage at minimum distance from Earth, Comet C/2023 A3 Tsuchinshan-ATLAS was visible to the unaided eye, despite the urban context, in the time frame between 7 and 7:30 p.m.” Thank you, Teresa!
A comet with the head at lower right and tail extending to upper left.
View at EarthSky Community Photos. | Steven Bellavia captured Comet A3 from Southold, New York, on October 12, 2024. Thank you, Steven!
Twilight sky with a comet above the trees.
View at EarthSky Community Photos. | David Hoskin in Farnham, Quebec, Canada, captured Comet A3 on October 12, 2024. David wrote: “I was delighted to be able to photograph C/2023 A3, which survived its close encounter with the sun and promises to improve as it climbs out of twilight this month.” Thank you, David!

There might be 2 comets in October’s sky


Here’s the lowdown on not one comet – but two comets – possibly visible in Earth’s skies in October and early November 2024. EarthSky’s Deborah Byrd, Marcy Curran and Dave Adalian have you covered! On October 8, astronomers said the 2nd comet, S1, might be disintegrating. More on that here.

Before this, it was in the sun’s direction

The comet was closest to Earth in its orbit yesterday, October 12, 2024. At that time, it was between us and the sun, putting on a heck of a show in solar telescopes. And some people even managed to catch it near the sun. See images below.

Sunset sky with a small white streak and a yellow arrow pointing to it.
View at EarthSky Community Photos. | David Chapman in Nova Scotia, Canada, sent us our first peek at Comet A3 in the evening sky. David took the photo just after sunset on October 11, 2024. David wrote that he detected the comet 45 minutes after sunset in binoculars and tracked it until it set at 7:45 p.m. He never saw it with his eye alone. It was dimmer than Venus and had a noticeable coma, but he didn’t see the tail. Thanks, David! The comet will rise higher in the sky every evening and become easier to see. Keep watching!
Colorful sunset with a faint comet above trees.
View at EarthSky Community Photos. | Eliot Herman in Tucson, Arizona, caught the comet on October 10, 2024. Eliot wrote: “On October 10, 2024, the comet was a tough spot especially given the poor dusty air quality in Tucson yielding vivid red sunsets. After seeing it at sunrise on Easter Island, I was very pleased to capture it on the other side of the sun.” Thank you, Eliot!

Comet A3’s orbit around the sun

Diagram showing orbits of planets and a swooping hyperbolic line swinging around the sun.
Comet C/2023 A3 (Tsuchinshan–ATLAS is a long-period comet, with an 80,000-year orbit around the sun. In this illustration, the turquoise line represents the path of A3 into the inner solar system. Its orbit around the sun is retrograde, meaning that the comet moves in the opposite direction to most major solar system planets. Its perihelion distance – closest point to the sun – came on September 27, 2024, when it was 0.39 astronomical units (AU, or Earth-sun distances) from our star. The comet was closest to Earth on October 12. Image via University of Arizona/ CSS/ D. Rankin.

Comet A3 in early October 2024

Comet C/2023 A3 (Tsuchinshan–ATLAS) reached perihelion, or its closest point to the sun, on September 27, 2024.

You can start looking as early as October 11, but from around October 14, Comet A3 will be easier to spot. The charts below show the comet’s location from around October 14 and following evenings. The comet’s great speed will cause it to appear noticeably higher in the western sky from one night to the next.

In late October, Comet A3 will pass rapidly in front of a series of constellations, including Serpens Caput and into Ophiuchus.

See our community photo gallery of the comet! It’s amazing.

Star chart showing tick marks higher above Venus near the horizon.
Around October 17, 2024, comet C/2023 A3 (Tsuchinshan-ATLAS) might be easier to see in the western sky, as the comet gets higher each subsequent night. Illustration by Eddie Irizarry using Stellarium.

How bright? How easy to see?

Comets are unpredictable. And there’s no way to know at this time exactly how bright any comet will become. But preliminary estimates suggest that Comet A3 might grow as bright as magnitude 2.5 to 2 during closest approach to Earth on October 12. Or maybe even slightly brighter if we are lucky (or fainter if we’re unlucky), since comet behavior is so difficult to predict.

So Comet A3 isn’t going to be a Comet of the Century. But if it continues to perform well, it might be the brightest comet of the year … except for one other possibility.

Two bright comets in October?

There is a second comet in Earth’s skies that might become bright, if it’s not disintegrating. The ATLAS telescope also discovered Comet C/2024 S1 (ATLAS). It’s what’s known as a sungrazer. It was first given the designation of A11bP7I, but now it’s officially C/2024 S1 (ATLAS) … or Comet S1 for short. Predictions for the comet had it reaching as bright as magnitude -5 to -7 around October 28. But on October 8, astronomers reported it might be breaking up. Read more about its rumored disintegration here.

Tsuchinshan-ATLAS: Starfield with one bright object and long, fuzzy streaking tail.
Efrain Morales captured this image of Comet A3 Tsuchinshan-ATLAS from Puerto Rico on July 8, 2024. Image via Efrain Morales/ Eddie Irizarry.

Helpful tips to spot a comet

1. Be sure you’re looking at the correct direction and time. Comet A3 will be visible low in the west after sunset beginning around October 14. Comet S1, if it holds together, will be visible in late October to early November, low in the east before sunrise.

2. You need a dark, unobstructed sky. Start looking when the sky is dark, but close to sunrise or sunset. Make sure there aren’t hills, trees or buildings blocking your view.

3. If you can’t see the comet with your eye, try your phone. Most cell phone cameras provide a night or low-light mode. But capturing an image of the comet will require that you hold the camera firmly – or lean against a fixed object like a tree – to avoid shaky or blurred images. Try taking a few pictures facing west after sunset (for Comet A3) or east before sunrise (for Comet S1). These images accumulate the light for a few seconds, so you might be able to catch the comet in your images, even if you can’t see it with the eye.

4. AFTER you’ve located the comet, use binoculars or your eyes to sweep in that area in the sky. You might discover that, in fact, you can see both the comet and its tail with your eye alone.

5. If you see it, try taking your own measurements of the comet’s tail. For example, if you take a good look through a pair of binoculars that has a 5-degree field of view, and you can see the tail extending about 3/5 of that field, you’re seeing around 3 degrees of the tail. And that means you are seeing with your own eyes a cometary tail that looks as long as six moon diameters!

Palm trees and a darkish sky with a comet near the middle.
Victor Rivera captured this image of Comet A3 using just his cell phone camera on Saturday, September 28, 2024, in Isabela, Puerto Rico. Used with permission.
Three images of the comet, with the left showing little tail and progressing toward the right.
Eddie Irizarry took these 3 images of Comet A3 – one every 2 days in late September – showing the tail looking increasingly longer. Used with permission.
A comet with a bright head and fuzzy tail extending to the upper right in a medium blue sky with a few stars.
Michael Mattiazzo captured this image of Comet A3 from Australia on September 17, 2024. Thank you, Michael! Used with permission.

A speedy ball of ice and dust

Comet Tsuchinshan-ATLAS is blazingly speedy. It’s tearing through the inner solar system at 180,610 miles per hour (290,664 kph) or 80.74 km per second relative to Earth. With a small telescope, you can actually see its amazing speed. You can watch the comet’s location gradually change by comparing its exact position against background stars just 15 minutes later.

Comet A3 Tsuchinshan-ATLAS’s disintegration rumors

Comet A3 Tsuchinshan-ATLAS hasn’t been acting as people expected it to. As it was approaching the inner solar system in early 2024, it wasn’t brightening as much as expected. And then a study suggested the cometary nucleus was fragmenting.

The paper’s author, Zdenek Sekanina, a Czech-American astronomer and comet expert at NASA’s Jet Propulsion Laboratory, said, on July 8, 2024, that the comet entered an advanced phase of fragmentation. He said the end of Comet Tsuchinshan-ATLAS was inevitable.

However, comets are notorious for being erratic and unpredictable. And this one proved to be as well.

Discovery and naming

The Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in South Africa discovered Comet C/2023 A3 on February 22, 2023. Additionally, observers at Purple Mountain (Zijin Shin or Tsuchinshan) Observatory in China found the comet independently on images from January 9, 2023. Therefore, the comet also has the nickname Tsuchinshan-ATLAS.

At discovery, the comet was still 7.3 astronomical units (AU) from the sun, and shining at a dim magnitude of 18.

Preliminary analysis of its trajectory suggests Comet A3 completes an orbit around the sun every 80,660 years.

Side by side images with gray background and black dots, with one dot in differint position in the panels.
View at EarthSky Community Photos. | Filipp Romanov captured these images showing movement of the new comet, originally labeled A10SVYR, and now officially C/2023 A3. Filipp took these images confirming the new comet with remote iTelescopes in Chile and Australia on February 24, 2023. Thank you, Filipp!

Comet A3 in social media

Getting up at 4am to see Comet Tsuchinshan-ATLAS rising over the Toowoomba range

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— George Zhou (@georgezhouastro.bsky.social) September 22, 2024 at 3:54 PM

Bottom line: Would you like to see Comet A3 Tsuchinshan-ATLAS in the evening sky? Get tips and star charts here. If you catch an image of it, submit it to us!

Source: Inevitable Endgame of Comet Tsuchinshan-ATLAS (C/2023 A3)

The post Want to see Comet A3? It’s back! West after sunset first appeared on EarthSky.

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