This story originally appeared on WIRE in Spanish and was translated from Spanish.
C/2023 A3, also known as Tsuchinshan–ATLAS and considered the “comet of the century”, will appear in all its glory in our sky in September and October 2024. Due to its properties, astronomers believe that it will be exceptionally radiant, similar to Halley’s comet in 1986 or NEOWISE in 2020.
Comets like C/2023 A3 are balls of frozen gas, rock, and dust that orbit the sun. They are often spectacular because of two physical phenomena that occur during their journey.
The first is a tail that extends from the comet’s nucleus as it approaches the star it orbits. Solar radiation from the star—in our case, the sun—evaporates some of the comet’s frozen material, blowing gas and dust away from the nucleus, which then reflects the star’s lithe. As the comet approaches its star, its tail grows larger because of the enhance in solar radiation.
The second phenomenon is the comet’s coma. This is a shell of sublimated ice that forms a kind of atmosphere around the nucleus as it approaches its star, also due to solar radiation. This also increases the comet’s brightness.
What is the best day to view a comet?
C/2023 A3 will shine in the northern hemisphere sky from September 27 and will remain perceptible until the last week of October. At that time, the comet will reach its minimum distance from the sun before beginning its return journey out of the solar system.
According to the specialist blog Cometography, the day when comet C/2023 A3 will shine its brightest will be October 2. The comet’s tail will be long and spectacular at that time due to its proximity to the sun.
What time will the comet be perceptible?
Because of its proximity to the sun, the comet will behave similarly to Mercury and Venus: it will be perceptible close to the horizon, in the path of the sun, and just before sunrise. The appropriate window to see it will be from 5 a.m. to 7 a.m. from September 27. The time and position will be similar across the northern hemisphere.
As October progresses, the comet will rise in position relative to the horizon and simultaneously fade in brightness. Because Tsuchinshan–ATLAS is a long-orbiting body and originates in the Oort cloud, beyond the edge of the solar system, it will not reappear in our sky for tens of thousands of years.