C/2023 A3 (Tsuchinshan-ATLAS)

There has recently been a lot of discussion about this comet in the media triggered by a paper by Sekanina which claims that the comet is disintegrating and would probably die before perihelion. Evidence from BAA observations does not support this assertion and, in fact, all the data we have shows a healthy comet which should make it through perihelion in September and, hopefully, give us a good show in October. Our photometry did show a stall starting in mid-April but the comet is now brightening again at around 1.2 mags below the pre-stall curve. The form of the lightcurve is explained by a combination of phase effects and the behaviour of dynamically new comets, such as this one, as it starts to be strongly heated by the sun.

Various observations imply a nucleus diameter of 2km which is quite large and also encouraging.

It is currently only visible in a dark sky from the southern hemisphere and we will probably lose it around mid-August. My thanks to all of the observers who have sent in data to the BAA.

As always, take any prediction about a comet’s future behaviour with a large grain of salt!

https://arxiv.org/abs/2407.06166
https://britastro.org/section_news_item/c-2023-a3-observing-campaign
https://britastro.org/cometobs/2023a3/index.html
https://www.simplelists.com/baa-comet/threads/2024/07/