There’s something magical about spotting a comet in the night sky. It’s like witnessing a celestial visitor from the distant reaches of space, making a rare appearance before vanishing back into the darkness. In fall 2024, comet C/2023 A3, or Tsuchinshan-ATLAS, will give us that kind of opportunity with the potential to deliver a truly spectacular display.
Discovered in January 2023 by two observatories — the Tsuchinshan Observatory in China and ATLAS (Asteroid Terrestrial-impact Last Alert System) in Hawaii — C/2023 A3 carries both names to reflect its dual discovery. C/2023 A3 is made of ice, dust, and rock, like other comets. However, unlike most comets that follow shorter elliptical orbits, this one is on a rare, extremely elongated orbit, meaning it will take around 80,000 years to return. To put that into perspective, the last time this comet passed through the inner solar system, much of the planet was covered by vast ice sheets, and early humans were beginning their migration out of Africa.
Astronomers believe C/2023 A3 originated in the distant Oort Cloud, a vast, spherical region filled with icy objects left over from the formation of our solar system. Located more than 50 times farther than the orbit of Pluto, the Oort Cloud is considered the outermost boundary of the Sun’s gravitational influence. While it remains unobserved mainly due to its immense distance, the Oort Cloud is believed to be the source of many long-period comets. Though it’s unknown exactly why C/2023 A3 originally left the Oort Cloud, gravitational interactions with other objects likely nudged it on its journey toward the Sun.
After traveling countless years from the farthest reaches of our solar system, C/2023 A3 made its closest approach to the Sun on 27 September 2024. Intense solar radiation caused the ice within its core to vaporize, forming a glowing coma, or “head.” At the same time, a tail of gas and dust stretched out behind it, setting the stage for a potential celestial spectacle. Despite the extreme conditions, the comet survived and is expected to brighten as it continues its journey toward Earth. Astronomers are optimistic that C/2023 A3 will deliver a rare and awe-inspiring display to all who witness it.
In the days leading up to 12 October 2024, when the comet will make its closest approach to Earth, it is projected to reach a brightness magnitude comparable to Venus. For the best viewing experience, seek out dark-sky areas far from city lights to avoid light pollution. Look toward the eastern horizon in the early morning, a few hours before dawn. As 12 October approaches, the comet will rise higher in the sky, becoming visible 30° to 40° above the horizon, depending on your location. The comet should appear higher in southern parts of the United States, while those in northern regions may spot it closer to the horizon.
After 12 October, as C/2023 A3 moves away from Earth, its brightness may fade, but it could remain visible for several weeks. Look toward the western sky just after sunset, where it may appear 10° to 20° above the horizon. Depending on the comet’s behavior, it could still offer impressive views through mid-to-late October.
As C/2023 A3 makes its closest approach to Earth, it offers a rare chance to witness a celestial event that won’t occur again for 80,000 years. Whether it shines brightly or stretches a brilliant tail across the sky, this comet’s journey will be a stunning reminder of the vastness of our universe. For those fortunate enough to see it, the memory of this extraordinary event will linger long after the comet has faded from view.