Space

Comet A3 is the brightest comet in 27 years! Don’t miss it

Posted by
Kelly Kizer Whitt
and
Eddie Irizarry
and
Deborah Byrd
and
October 15, 2024
A comet behind bright streetlights.
This comet is bright! EarthSky founder Deborah Byrd caught Comet A3 on the evening of October 14, from downtown Austin, Texas. See it behind the streetlights (above and to the right)? She said: “It wasn’t easy to spot. I was sitting right next to a highway, and there were big streetlights all around. I spent maybe half an hour shooting the part of the sky where I THOUGHT the comet should be with my iPhone. I also scanned with binoculars. Finally, the binoculars picked it up. Then, as the sky darkened, I realized I could see a faint smudge with the eye alone.”

Brightest comet in 27 years!!

In case you haven’t heard … Comet C/2023 A3 (Tsuchinshan-ATLAS) – aka Comet A3 – is in the evening sky! And it’s the brightest comet in 27 years, the brightest since Hale-Bopp in 1997. Look to the right of the bright planet Venus for Comet A3’s long wispy tail. Read and find more charts: Can you see Comet A3 Tsuchinshan-ATLAS with the unaided eye?

Our charts are mostly set for the northern half of Earth. To see a precise view – and time – from your location, try Stellarium Online.

Star chart showing Venus and the comet.
Watch for C/2023 A3 (Tsuchinshan-ATLAS) – aka Comet A3 – this week to the right of the bright planet Venus, in the west not long after sunset. As the days pass, the comet will be appearing higher above the western sunset horizon. See the chart below. Illustration by Eddie Irizarry using Stellarium.
Star chart showing a comet with tail pointing up for 2 dates, 1 closer to the horizon and 1 higher up.
Here’s a chart for October 14 to 24. Look to the west shortly after sunset. Notice that Comet A3 will appear higher above the western horizon after sunset each evening. Binoculars and a dark sky will help! Chart via EarthSky.

Comet A3 and its anti-tail, October 13-15

Comet A3 has an anti-tail! Can you see it? An ordinary comet tail always points away from the sun. That’s because comet tails are created by the pressure of solar radiation and by the solar wind streaming from our star. But – during the period of October 13 to October 15, as we cross the plane of the comet’s orbit – Comet A3 is exhibiting a rare anti-tail as well. The anti-tail points toward the sun. Read about the anti-tail – and see photos – here.


Victor Rivera in Puerto Rico captured this rare footage of the anti-tail of Comet A3 on October 13, 2024.

We might have 2 comets

Stay tuned, because we might have another bright comet toward the end of October. EarthSky’s Deborah Byrd, Dave Adalian and Marcy Curran have more in the video below.


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.

Look west after sunset for Comet A3

In September and early October – for Southern Hemisphere observers with dark skies and good optical aid – Comet C/2023 A3 (Tsuchinshan–ATLAS) put on a fantastic show in the morning sky. Amazing images of A3 in the morning 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 western 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 October 12. So it’s now moving away from us, and thereby getting fainter. And yet, in the days ahead, the comet should 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 will be farther each evening from the sun’s glare.

Here are some images from the EarthSky community.

Twilight sky with trees in foreground and small comet in the sky next to an old-fashioned Texas windmill.
View at EarthSky Community Photos. | Scott McDonald captured this image from Fort Worth, Texas, on October 12, 2024, and wrote: “Perfect weather and sunset for capturing Comet C/2023 A3. I drove down the road a bit and found this old windmill to use, pulled off the road and got a few good shots, this is one of them.” Thank you, Scott!
Long-tailed comet over a distant mountain and foreground city lights.
View at EarthSky Community Photos. | Azem Ramadani captured this image from Kosovo on October 14, 2024, and wrote: “Comet C/2023 A3 Tsuchinshan-Atlas. Captured about an hour after sunset, shortly before setting behind Pashtrik mountain. Photo taken from the city of Prizren, Kosovo, with lots of light pollution.” Thank you, Azem!
Comet in twilight, near a tall silhouetted saguaro cactus and above distant city lights.
View at EarthSky Community Photos. | Dale Ann Petersen captured this image on October 13, 2024, from Oro Valley, Arizona. Thank you, Dale Ann!

Before this, the comet was in the sun’s direction

The comet was closest to Earth in its orbit on 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.

Around October 17 …

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 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.

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!

Venus and comet in a twilight sky over some trees.
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 with longer tail.
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.

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. However, that doesn’t mean it’s been here before or will be back in 80,000 years. According to Karl Battams, a scientist who works on the SOHO/LASCO and Sungrazer Project for the U.S. Naval Research Laboratory, the comet is most certainly dynamically new from the Oort Cloud and it’s not possible to model back if it had been near the sun in the ancient past. Battams also said:

Its orbit has now been tweaked (shortened) by the sun but still is absurdly long, and puts it back out into the Oort Cloud where, more than likely, it’ll get nudged again by a passing star system, and will never return. … So Neanderthals definitely did NOT see this comet, and some distant alien civilization is more likely than humans are to see it.

Side by side images with gray background and black dots, with one dot in different 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

[image or embed]

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

Bottom line: Look for Comet A3 Tsuchinshan-ATLAS in the evening sky, west after sunset. Get tips and star charts here. If you catch an image, submit it to EarthSky!

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

Posted 
October 15, 2024
 in 
Space

Kelly Kizer Whitt

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About the Author:
Kelly Kizer Whitt - EarthSky’s nature and travel vlogger on YouTube - writes and edits some of the most fascinating stories at EarthSky.org. She's been writing about science, with a focus on astronomy, for decades. She began her career at Astronomy Magazine and made regular contributions to other outlets, including AstronomyToday and the Sierra Club. She has nine published books, including a children's picture book, Solar System Forecast, and a young adult dystopian novel, A Different Sky.

Eddie Irizarry

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About the Author:
Eddie Irizarry of the Sociedad de Astronomía del Caribe (Astronomical Society of the Caribbean) has been a NASA Solar System Ambassador since 2004. He loves public outreach and has published multiple astronomy articles for EarthSky, as well as for newspapers in Puerto Rico. He has also offered dozens of conferences related to asteroids and comets at the Arecibo Observatory. Asteroid 33012EddieIrizarry, a 7.8 km space rock, has been named in his honor.

Deborah Byrd

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About the Author:
Our Editor-in-Chief Deborah Byrd works to keep all the astronomy balls in the air between EarthSky's website, YouTube page and social media platforms. She's the primary editor of our popular daily newsletter and a frequent host of EarthSky livestreams. Deborah created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. In 2020, she won the Education Prize from the American Astronomical Society, the largest organization of professional astronomers in North America. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.

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