2024 April 21

Comet C/2023 A3 (Tsuchinshan-ATLAS) Observing campaign

Nick James

C/2023 A3 (Tsuchinshan-ATLAS) was discovered at the start of 2023 when it was 7.5 au from the Sun. It has the potential to be a bright comet in the evening sky this October.  The comet has been brightening slowly over the last year and it is now approaching a total magnitude of around 10 as it comes within 3 au of the Sun. It also shows a short tail to the east. The tail is actually pointing almost directly away from us so this short tail is a projection of a much longer tail onto the plane of the sky.

The comet is a good imaging target in the evening sky for the next few months before it disappears into the evening twilight. This objective of this observing project is to track the near nucleus brightness of the comet in order to identify any outbursts. This project uses an identical technique to the one used for 12P/Pons-Brooks in that we are using a nominal 9 arcsec radius photometric aperture with Astrometrica, unfiltered imaging and Gaia G as a reference catalogue. Details of how to contribute to the C/2023 A3 observing programme and submit your observations are here. The current magnitude in the 9 arcsec aperture is around 12.

So far the lightcurve is not very interesting but, as with all comets, we never quite know what to expect so please send in your observations. If possible please also send in observations made earlier this year or last year so that I can add the data to the lightcurve and fill in the big gap between 2023 June and 2024 March although for some of this time the comet was unobservable since it was in conjunction.