C/2023 E1 (ATLAS)

C/2023 E1 (ATLAS) is a periodic comet with an orbital period of 85 years. It fits the classical definition of a Halley-type comet with an orbital period of between 20 and 200 years. The comet was discovered on 1 March 2023 by ATLAS South Africa. Upon discovery, the comet had an apparent magnitude of about 19 and had a very condensed coma. The comet was subsequently precovered in images obtained by other observatories back on 25 December 2022.

The comet brightened in late June to a magnitude of +10, and became visible in small telescopes and binoculars. At that time it was located high in the northern skies, in the constellation of Little Dipper. It passed its perihelion on 1 July and reached an apparent magnitude between 8 and 9. The comet had a greenish coma and a faint narrow ion tail. On July 8 it passed 9 degrees from the north celestial pole. The closest approach to Earth was on 18 August, at a distance of 0.375 AU.

The comet seems to be in a 2:1 orbital resonance with Neptune, with the comet completing two orbits for every orbit Neptune does.