Comet Tsuchinshan-ATLAS (C/2023 A3)

24 October 2024 Long exposuresNanosNightPostojnaViewTime-lapseStars

Comet Tsuchinshan–ATLAS angles across the starry twilight above a dark mountain ridge and scattered lights in the valley.

After the monsoon period came three clear days. The peak, when the comet was closest to Earth at 71 million kilometres, or 0.47 AU (47% of the average distance from Earth to the Sun), was in the previous week (12 October 2024). The comet is now moving rapidly away from us and by the end of October 2024 it will already be 1.94 AU, or 290 million kilometres, away.

Comet Tsuchinshan-ATLAS hangs faintly above the glowing night lights of Postojna and the dark outline of surrounding hills.

Comet C/2023 A3 Tsuchinshan-ATLAS over Postojna

Over three nights of chasing the comet, I tried from four different locations: Strmca, Zalog (Postojna), Pečna reber and Šilentabor.

Comet Tsuchinshan–ATLAS and its pale tail appear above the dark ridge of Nanos and scattered valley lights.

Comet C/2023 A3 Tsuchinshan-ATLAS over Nanos (photographed from Strmca)

The comet is named after the two observatories that first observed it.

The Purple Mountain Observatory at Zǐjīnshān Tiānwéntái in China (紫金山天文台), and the
ATLAS system (Asteroid Terrestrial-impact Last Alert System) in South Africa.

Comet Tsuchinshan–ATLAS glows faintly above a starry sky and the white church at Zalog near Postojna.

Comet Tsuchinshan–ATLAS streaks above an illuminated cross and dark trees in the starry sky over Zalog near Postojna.

Comet Tsuchinshan–ATLAS appears beside the illuminated metal cross at Zalog near Postojna under a deep blue night sky.

Photographed from Zalog near Postojna (St Daniel's Church)

Comets are made of rock, ice, carbon gases and other dust particles, and range from a few kilometres to tens of kilometres in diameter. Their characteristic tail appears when a comet approaches the Sun and the heat causes the ice in its nucleus to sublimate, creating gas and dust that are dispersed into a tail by the solar wind.

A starry purple sky and faint comet rise above St Martin's Church at Šilentabor, lit against bare trees.

On the third night at Šilentabor (the subject is St Martin's Church), we photographed it together with Matej Blatnik.

Comets have two main types of tail: an ion tail, which consists of charged particles and points directly away from the Sun, and a dust tail, which is wider and more curved because of the particles' lower speed.

A faint comet rises through a deep blue evening sky above Postojna, whose lights glow below the dark horizon.

Photographed from Pečna reber (Mladika Lodge)

Claims that the comet has an orbital period of 80,000 years and was last seen by Neanderthals are probably wrong. According to new calculations, the comet will continue on its path around the Sun beyond the Solar System and will not return.

Animated orbital diagram tracing comet C/2023 A3 around the Sun among labelled planetary paths and dated positions. — *Animation of the comet's close encounter*

Comets follow very unpredictable paths, so it is difficult to determine their origin and future. Sometimes they do not survive encounters with stars and "evaporate".

Two time-lapse sequences were also made during the photography.