New comet – C/2023 A3 Tsuchinshan – could be bright in 2024

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, a 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.

A beautiful, graceful cometary apparition might be in store for us. It’s been a while since we’ve had a wispy comet tail stretch across our evening sky. In October 2024, in particular October 14 through 24, C/2023 A3 (Tsuchinshan-ATLAS) could be bright in the early evening sky. With ten months to go, all looks good for a great showing.

The comet will make its closest approach to the sun (its perihelion) on September 28, 2024. At that point, some estimates are suggesting it might be around magnitude 0.7. That brightness rivals some of the brightest stars in the sky (though, for comets, the brightness is diffuse, not in a single point).

And of course, as with all comets, be aware that they are finicky balls of ice and dust, often not living up to expectations.

The turquoise line represents the path of Comet C/2023 A3 into the inner solar system. The comet will be closest to the sun on September 28, 2024, and closest to Earth in October 2024. Image via University of Arizona/ CSS/ D. Rankin.

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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 18.

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!

Where’s the comet now?

Preliminary analysis of its trajectory suggests comet “A3” completes an orbit around the sun every 80,660 years. As of the end of 2023, we see Comet Tsuchinshan in the direction of the constellation Libra. Distance-wise, it’s now between the orbits of Jupiter and Mars. Closest approach to Earth should occur on October 13, 2024, at 05:38 UTC.

An amazing detail of the comet is its blazing speed: 180,610 miles per hour (290,664 km/h) or 80.74 km per second, relative to Earth.

When does the fun begin?

Amateur astrophotographers in the Northern Hemisphere may start getting good images of the approaching comet by early June 2024, as the visitor glides by the constellation of Virgo. The comet gets lost in the glare of the sun by August 2024. Then it passes at perihelion – or closest to the sun – on September 28, 2024. Observers with an unobstructed view of the eastern horizon might get a view of the comet during perihelium, especially if the visitor develops an impressive tail.

The development of a nice tail is a possibility, because the comet will be a lot closer to the sun than the planet Venus. In fact, it will be so close to our star that during perihelion, comet A3 will be skimming the orbit of planet Mercury. However, this closeness to our star comes with a known risk for comets; the possibility of disintegration. That’s the reason why there is a current debate on whether this comet will or will not survive its approach to the sun.

If comet A3 survives perihelion, it’ll be too close to the eastern horizon during its closest approach to Earth. The good news is that the high speed of the comet will get it higher in the sky during the following nights after passing by our planet, thus making it easier to spot in the western sky.

Closest approach to Earth

Its closest approach to Earth comes on October 13, 2024. At that point, it could be bright enough to reach magnitude -0.2. As it passes between Earth and the sun, forward scattering could make the comet appear even brighter. The reflection of sunlight off the dust and ice could enhance its light in our direction, making it brighten considerably, up to magnitude -5. That is, if it survives.

The path of Comet C/2023 A3

After the comet gets closest to the sun, it will swing around near Earth. But as it does so, it passes almost directly between Earth and the sun, making it challenging to view. In early October, the comet will be in the dawn sky in Leo and near the constellations Hydra and Crater.

Then in late October, as it appears on the other side of the sun, it will move into the evening sky, passing through Serpens Caput and into Ophiuchus.

Finder charts for C/2023 A3

Chart showing partly lit moon high above tick marks showing comet location at lower right.
Comet C/2023 A3 on September 28, 2024 (perihelion). Facing east just before sunrise. Illustration by Eddie Irizarry using Stellarium.
Chart showing dot for Venus near trees and tick marks for comet slightly higher to the right.
Comet C/2023 A3 on October 14, 2024, one day after closest approach to Earth. Facing a western unobstructed horizon just after sunset. Illustration by Eddie Irizarry using Stellarium.
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.

Bottom line: A newly discovered comet, C/2023 A3 (Tsuchinshan-ATLAS), could be quite bright in October 2024.

March 3, 2023

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