C/2023 A3 (Tsuchinshan-ATLAS) is a long period comet discovered by ATLAS South Africa on 22 February 2023 and independently found in images by the Purple Mountain Observatory taken on 9 January 2023. The comet will pass perihelion at a distance of on 28 September 2024, when it is expected to become visible by naked eye. Observational history During the search perfomed by Asteroid Terrestrial-impact Last Alert System using the 0.5-m f/2 Schmidt reflector at the Sutherland Observatory in South Africa an asteroidal object with an estimated magnitude of 18.1 was detected in images taken on 22 February 2023, when the comet was about from the Sun. After the first orbit calculations it was noticed that it is the same as an 18.7 magnitude object reported to the Minor Planet Center by the Purple Mountain Observatory that was detected in images taken on 9 January 2023. It was entered in the objects waiting confirmation list but after no follow up observations were reported, it was removed in 30 January 2023 and was considered lost. Based on the naming convections of comets, the comet received the name of both observatories. The object was subsequently detected in images taken by Zwicky Transient Facility (ZTF) in Palomar Observatory on 22 December 2022, when it had a magnitude of 19.2-19.6. These images also revealed it had a very condensed coma and a small straight tail 10" in length, indicating it is a comet. More evidence of cometary activity were reported by Hidetaka Sato, M. Mattiazzo, and Cristóvão Jacques. Upon discovery announcement the comet was estimated to reach a total magnitude of +3 during perihelion, assuming that an absolute magnitude (H) of 7 and 2.5n = 8, when it will be in low solar elongation. It will become better visible from Earth about three weeks after perihelion, after mid October, when it is estimated to be of forth magnitude. Gideon van Buiten estimated that the comet will reach a magnitude of 0.9 during perihelion and -0.2 at the time of the closest approach to Earth, assuming H = 5.2 and 2.5n = 10, and without taking into consideration the effects of forward scattering. Orbit The comet has a retrograde orbit, lying at an inclination of 139°. Τhe comet has its perihelion at a distance of 0.39 AU and the closest approach to Earth will be on 13 October 2024, at a distance of 0.47 AU. The