Status Report and Expectations for Comet Tsuchinshan-ATLAS

By: Bob King August 14, 2024 14

Is Comet Tsuchinshan-ATLAS falling apart? How bright will it likely get? We try to answer those questions and more.

C/2023 A3 from Namibia — In spring, most observers saw only Comet Tsuchinshan-ATLAS's dust tail. It's now joined by a delicate ion tail beautifully captured here on July 28th. The comet reaches perihelion on September 27th.
*Gerald Rhemann*

You might need help pronouncing the name of the comet that's on all our lips these days. As imperfect as it is, Choo-cheen-SHAHN - ATLAS comes close. The Oort Cloud dropout is currently located a little more than one astronomical unit (a.u.) from the Sun and barreling into the inner solar system at around 144,000 kilometers per hour. Through the telescope, Comet Tsuchinshan-ATLAS (C/2023 A3) glows around magnitude 8.5 with a compact coma several arcminutes across with a ½° tail pointed east-southeast.

Mid-northern latitude observers lost it to evening twilight in mid-July but folks in the Southern Hemisphere can still spot it in large binoculars or a telescope low in the western sky at dusk. Time is running short — the current observing window will close within a week. Then the icy visitor will hide in plain sight in the daytime sky until late September.

Comet Tsuchinshan-ATLAS in August — Comet C/2023 A3 is still alive and kicking. We see it here on August 10th with a 2.8′ coma and 16.9′ tail in P.A. 100°. North is up. Up-to-date information on the comet's brightness, coma size, and tail length can be found at the Comet Observation database (COBS).
*Taras Prystavski*

Despite some recent news to the contrary, the comet appears healthy — it's brightening smoothly in accordance with expectations — and so far gives no indication of breaking up or disintegrating. Some of us were concerned when it stalled out and then faded in April and May after steadily brightening during the winter months. In Inevitable Endgame of Comet Tsuchinshan-ATLAS (C/2023 A3), published this July, astronomer Zdenek Sekanina suggested a crumbling nucleus could be behind the dip in brightness.

Other comet experts begged to differ, attributing its bright appearance in March to the opposition effect and subsequent fade to simple orbital dynamics. When the Moon lies directly opposite the Sun at full phase, shadow-hiding and other factors boost its surface brightness from Earth's perspective. The comet briefly experienced the same. Once C/2023 A3 passed opposition, the effect abated and the comet dimmed somewhat. Then from late May through late July, even as it continued to approach the Sun, it temporarily receded from Earth, extending its faint spell and making it appear as if something was amiss. Now that Comet T-A's distance is shrinking once again, it's been steadily gaining ground and brightening.

C/2023 A3 light curve — The light curve charts the estimated development of C/2023 A3's brightness. Blue and black dots are visual and photometric CCD observations, respectively, from the COBS (Comet Observation database) or MPC (Minor Planet Center). The gray curve is based on data from the original MPEC (Minor Planet Electronic Circular) or the latest values from the MPC. The red curve is based on fresh observations from MPC / COBS. The green curve shows the potential effect of forward scattering. Under ideal circumstances the comet could reach about magnitude –1 in early October.
*Gideon van Buitenen*

So far there's been no visual or photographic evidence that the nucleus is disintegrating. The light curve is normal and the comet appears on track for a fine appearance this autumn. That doesn't mean we're out of the woods yet. Perihelion can be perilous. Grilled by the Sun's heat and flexed by its gravity the comet could still potentially suffer a breakup.

Based on current observations, the comet is expected to peak around magnitude 2 or 3 when it returns at dawn in late September and again after it transitions into the evening sky in mid-October. Viewing circumstances favor an additional boost in brightness due to forward-scattering of sunlight by fresh dust released during perihelion passage. Should that occur, C/2023 A3 may flirt with magnitude –1 at these times. It's good to remember that while light curves are guidelines to help us anticipate a comet's appearance, it's under no obligation to comply.

For telescopic comets, light curves often include electronic observations that typically measure only the innermost coma as well as estimates made with larger amateur telescopes. Both tend toward the faint side. Jonathan Shanklin, coordinator of the British Astronomical Association's Comet Section, notes that observers using the naked eye or binoculars will typically estimate a brighter magnitude. Check out his light curve for C/2023 A3.

Comet Tsuchinshan-ATLAS — C/2023 A3 returns to the morning sky in late September. Be sure to find a viewing site with an unobstructed eastern horizon for the best chance to see it. From latitude 40° north the comet will hover only a few degrees above the horizon 45 minutes to an hour before sunrise during the final week of September and first few days of October. Circumstances are better for observers near the equator where the comet will stand more than twice as high at dawn.
*Sky & Telescope*

Since the comet will be brightest when low in the morning and evening sky, finding locations with good horizons are important — east for its morning appearance and west for October's evening apparition. As Comet Tsuchinshan-ATLAS moves farther from the Sun and into a dark sky in October, the more rural your observing site the better. Tails are diaphanous things best seen far from LEDs.

Comet C/2023 A3 tail simulation — This simulation anticipates two apparition highlights — the growth of an approximately15° dust tail and even longer gas tail from September 28th through October 2nd. When C/2023 A3 climbs away from the Sun in the evening sky, its dust tail will stretch about 10°, with a gas tail possibly as long as 40°! Viewing circumstances at dusk are also ideal for viewing the comet's antitail, which may rival that of Comet Arend-Roland in 1957.
*Nicolaus Lefaudeux*

In late July, French optical engineer and amateur photographer Nicolas Lefaudeux posted some well-received visual simulations on the Comet Mailing List anticipating the appearance of C/2023 A3's tail and antitail during its autumn appearance. I was excited to learn that the dust tail may reach a maximum length of around 30° on October 9th during solar conjunction. From a dark-sky site it may be possible to see or photograph the top third of the tail above the horizon while the Sun is still 20° below the horizon. I'm all in on that! Drop by his Comet Tails Simulations site for full details.

Comments

Zubenelgenubi 61

August 16, 2024 at 10:15 am

For a long time, the expectation was that A3 might attain zero magnitude, so reaching a peak of mag. 2 or 3 would be a disappointment. Given the moonlight and twilight the comet will face it doesn't look like it will be a very impressive visual object, although imagers no doubt will have a field day. Best probably around Oct. 14 at around mag. 4. Have to hope for a surge while hidden by the Sun. If the forward scattering event occurs, it will be while the comet is buried in bright twilight- it might make it somewhat visible but dimmed greatly.

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Bob KingPost Author

August 16, 2024 at 11:22 am

Zubenelgenubi,

It does seem as if expectations should be lowered, but C/2023 A3 appears to be a dusty comet and circumstances favor forward scattering and the appearance of an anti-tail. If 2nd magnitude is as good as it gets the comet and its tail will be delicately beautiful with the naked eye (from a dark sky) and an eyeful in binoculars. I'm reminded of the current 13P/Olbers. Given its low altitude throughout much of its this summer's apparition I didn't expect much, but it has exceeded my expectations both visually — with a bright, dense coma and obvious tail — and photographically, with its picturesque tails and fan. If you haven't already seen images by Dan Bartlett (and others) of 13P I encourage you to look them up.

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Chris-Schur

August 17, 2024 at 2:34 pm

Great article Bob! I have a great view of the eastern horizon from my balcony and we will certainly be out on every clear morning to catch that tail before the head rises. My thought is to use the mount to accurately point at its position before it rises and see what shows up in the image as the horizon becomes into the frame.

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Bob KingPost Author

August 17, 2024 at 3:41 pm

Thanks, Chris. That's an excellent plan. I will do something similar using a telephoto on a tracking mount.

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Elvino DrivingAlgarve

August 22, 2024 at 11:38 am

Bob: Nostradamus has predicted around 1555, not 1999 as you said, not only this daylight comet but also the 1st and 2nd WW but much more like the 27 years Putin war against Ukraine (1999 till 2026), the destruction of the Nord Stream gas pipeline, the war in Irak, Napoleon and so many more. Yet to come the Putin revenge (Wagner african group invading west Europe), etc... it is better to stop telling the future... people will beleive when they see only...

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Elvino DrivingAlgarve

August 18, 2024 at 8:02 am

Hi all this comet is incredible. Beleive me: I was expecting it for 27 YEARS. Why? I bought a book around 1997 that describes this comet exactly what you can read today.
- it is a daylight comet
- people on Earth may see it near the sun (like two suns)
- it passes in Leo constellation
- it passes very close to the Earth
- it may disintegrate spreding rocks around
I seriously HOPE the book is wrong:
- in its tail a few big rocks may hit the Earth (the seventh specialy will hit the Atlantic ocean).
- the damage on Europe, USA and other countries will be huge and nobody have thought about. It is better to stop telling you the content of the book!!!
I recommend all of you to read this book if you can find it. "Nostradamus 1999" by Stephan Paulus.

- the destructon

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Bob KingPost Author

August 18, 2024 at 11:10 pm

No worries, Elvino. The book is completely wrong. You can sleep peacefully knowing the comet poses no threat whatsoever. It won't pass close to the Earth, won't be particularly bright (not visible in daylight), it's barely in Leo (spends most of its time in Virgo and Serpens when closest), and if it disintegrates will basically turn to dust — and that dust will be far from Earth. Instead, Comet Tsuchinshan-ATLAS will become a beautiful and delicate sight low in the western sky at dusk in mid-October. If you don't already have binoculars, make sure you get a pair so you can see it best.

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Elvino DrivingAlgarve

August 19, 2024 at 7:14 pm

Hi Bob how can you be so shure if a great scientist like Mr Sekanina was so confident that he wrote that study for the world to know that this comet may disintegrate???
What elements you have that l don't to say "the book is completely wrong"?
Did you read the book? If not please do it and see for yourself. After that we will talk about ...

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Bob KingPost Author

August 20, 2024 at 12:12 am

Elvino,

Always glad to discuss. I reported what other knowledgeable comet observers have written in response to Mr. Sekanina's analysis. Some feel the paper misses key points that indicate a different cause for the comet's light changes. Frankly, there is zero observational evidence of breakup then or now. Predictions by Ignacio Ferrin were part of Sekanina's paper. Ferrin, who touted the comet's disintegration, has since revised his position and now says that it's no longer fragmenting but sublimating rapidly. I have yet to see any analysis of this new scenario.

Regarding the Nostradamus book — it is not possible to predict in 1999 that a specific comet would be discovered in 2023 that would disintegrate and create the havoc you described. There is no way any astronomer would or could ever make that prediction — it defies logic. And while the author may be a talented and brilliant writer his biography indicates no background in astronomy. I've been around long enough to have heard numerous doomsday scenarios involving comets that never materialized. Many of these predictions are based on misunderstanding the nature and behavior of comets.

Lots of comets disintegrate. It's not uncommon. In fact, as I described in the article, there still exists the possibility that C/2023 A3 will break apart. We'll just have to keep watching and let the comet do what it will do. I for one hope it holds onto its head!

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PeteBA

August 21, 2024 at 10:31 am

Thank you for this great article. I have a 7 year old here interested in astronomy that I recently told about this comet. However, I'm unsure whether I should hype up the possibility of him being able to see it at all (and the risk of possible disappointment) as we live in the city of Buenos Aires and the possibility of it not reaching great brightness levels. But, on the 2nd of October at about 4pm there will be a partial eclipse in this area. Any chance in the dimmed light at the horizon it'll be visible with the naked eye. The coming together of a couple of celestial events might really spark his enthusiasm for the topic. Thanks

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Bob KingPost Author

August 21, 2024 at 12:34 pm

Hi Pete,
I think it's wonderful you want to show your 7-year-old the comet. You're right about Buenos Aires — light-pollution and buildings may make it impossible to see. Unfortunately, only about 41 percent of the Sun will be covered during the eclipse from your location so the sky will be too bright to see the comet. Your best opportunity will be in the last two weeks of October when the C/2023 A3 moves into the evening sky and climbs away from the Sun. It will likely still be around 2nd magnitude in mid-October and gradually fade but still be easily visible in binoculars throughout the month. There will be a bright Moon for a time until about Oct. 18th. We'll be covering the comet's development on the S&T website and have the latest news so you can know what to expect. Here's what you'll need:
1. A pair of binoculars for the best view. 10x50s, 8x40s should be fine.
2. Find a location to the west of the city with an unobstructed view of the western horizon. That will be crucial especially when the comet is brightest, which occurs at same time it's low in the sky.
3. Let Venus be your guide. It will be shine brightly in the west at the same time as the comet. Hold a balled fist at arm's length against the sky and look about two "fists" to the right and below Venus to spot the comet.

Good luck! I hope you both get to see it.

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PeteBA

August 21, 2024 at 2:46 pm

Thank you for your time and information, appreciated

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Elvino DrivingAlgarve

August 22, 2024 at 11:59 am

PeteBA: as this comet has been predicted by Nostradamus in the XVI century, you will see it next to the sun ("as 2 suns in the sky). You just have to be in the right place in the south of Argentina or Chile.
Read in Wikipedia: Other than Easter Island and a small portion near the southern tips of Argentina and Chile and the north of the Falkland Islands, the path of the eclipse's antumbra will be entirely over the Pacific Ocean. The penumbra will be visible from Hawaii, eastern Oceania, southern and central South America, the southwesternmost parts of Mexico (more specifically, Baja California del Sur and Jalisco), and portions of Antarctica. Approximately 175,000 people live in the path of annularity.

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Bob KingPost Author

August 23, 2024 at 11:08 am

Pete and other readers,
I should add that Comet Tsuchinshan-ATLAS may reach magnitude 2 on Oct. 2, the day of annular eclipse. This is about as bright as the stars in the Big Dipper. Since it will lie only about 20° from the Sun it will be impossible to see with the naked eye. If however it breaks up around perihelion, it could be brighter or fainter than this prediction — most likely the latter. As of late August, the comet shows no signs of falling apart.

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