The comet’s closest approach to the Sun, or perihelion, won’t be until September 28, 2024, before it hits its closest point to Earth a few weeks later on October 13, so you’ll have plenty of time to get your blanket and telescopes organized.
Although estimates are extremely preliminary, astronomers predict a luminosity on the order of 0.7 at the comet’s perihelion. Keeping in mind numbers lower on the magnitude scale represent brighter objects, with Betelgeuse in the constellation Orion at around 0.42, and Antares – the brightest star in the constellation Scorpius – slightly fainter at a pressure above 1.
At its closest point to Earth, the comet’s magnitude could reach an even more dazzling -0.2, which would make it one of the brightest objects in the night sky. Add the effects of forward scattering, where the comet’s dust and ice reflect light from the Sun, and we can even reach a magnitude of -5.
Unless its encounter with a star tears it apart before it swings out again on its way into the outer solar system, that is.
It’s also worth bearing in mind that the comet’s brightness is more diffuse than the star’s brightness, since we’re talking about a moving object with (potentially) a tail rather than a single source of illumination.
The best moments to see C/2023 A3 should be the days before or after October 13. It will appear in the morning sky near the constellations Hydra and the crater, but be warned, getting a good view in the glow of the sunrise will prove difficult.
Astronomers first spotted C/2023 A3 on January 9, 2023 from the Purple Mountain Observatory in China. It was then thought to be lost before being picked up again by the team at the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in South Africa on 22 February 2023.
As a result, it gets both institute names in its own name (“tsuchinshan” is Mandarin for “purple mountain”). C is used for comets on an open orbit (probably escaping the Sun’s orbit), 2023 is the year of discovery, and A3 shows that this was the third discovery in the first half of January (B is the second half of January, C the first half of February, and so continue).
In addition to its remarkable luminosity, C/2023 A3 is traveling particularly fast: about 180,610 miles or 290,664 kilometers per hour, zooming along on a long circuit of the solar system, estimated to take approximately 80,660 years. Right now it is somewhere between the orbits of Saturn and Jupiter.
Stargazers should start getting good observations of the comet in June 2024, although there’s a lot of (educated) guesswork involved here: these celestial bodies can be unpredictable in the way their paths evolve, and scientists know little about this comet’s properties.
While the chances are good that we’ll see C/2023 A3 shining bright in the sky next year, there isn’t much in the way of comparable cometary data to base calculations on. As such, astronomers can’t even say for sure whether the poor old ball of rock and ice will stay intact long enough to make its deal with the Sun.
Despite the uncertainty, it’s an exciting prospect for astronomers, and we’re likely to hear a lot more about C/2023 A3 over the coming months.