Comet C/2023 A3 Tsuchinshan-ATLAS was a bit of an unexpected guest in the solar system. It was discovered at the beginning of 2023 when its brightness was about 18mag. The distance to the comet was 1.2 billion km then and was located in the constellation of Libra.
Over one year later, in May 2024, the comet was visible in the constellation of Virgo. The distance to it shrank to 250 million km, brightness increased to 10mag, and during one of my live stacking sessions, I captured the comet using an 8-inch SCT telescope.
The image above was made with an ASI 183MM Pro camera, and this is 5 minutes of total exposure time in 4-second subframes.
The comet was already expected to brighten up to 0mag in September 2024, so everybody was looking forward to it very hard. Unfortunately, the northern hemisphere observers needed to wait till the beginning of October to see the comet just after it reached the maximum brightness. Conditions were far from good, because the comet was low above the horizon, and also the Moon phase was almost full.
Eventually, on October 15th, 2024, I captured a moment of clear sky in the evening and imaged the comet C2023 A3 Tsuchinshan-ATLAS. It was moving across the Serpens constellation, apparently next to the M5 globular cluster. It was visible with the naked eye, though it was not spectacular, because the evening sky was still quite bright, and it never got dark that night due to the Full Moon.
The comet was about 70 million km from Earth. The image below was made with a Sony A7III camera with an 85mm lens attached. It is a single exposure of 3s.
Despite unfavorable conditions, this short exposure image shows the target quite nicely. The comet’s head was very bright, the tail was quite long, and also the anti-tail was visible. The fuzzy star above the comet’s head is actually the M5 globular cluster in Serpens.
Comets that bright are not common visitors in the sky. They show once per decade on average, but you will never know when exactly it will be. Periodic comets are easy to track, but they do not become that bright. It must be a comet that was never or is extremely rare close to the Sun, so it contains a lot of matter that can be vaporized when heated. And, of course, it must come close to the Sun. This process creates a large head, a long tail, and spectacular views for us.
