Two Comets Could Be Visible to the Naked Eye This Fall. Here’s How to Get the Best View

This fall, not one but two comets could be visible to the naked eyes of curious stargazers, gracing Earth’s skies with a new glow.

One of them, called C/2023 A3 (Tsuchinshan-ATLAS), is already visible. The second comet was just discovered last week, and if all goes well for skywatchers, it could become brighter than Venus around the end of the month.

But astronomers note that the comets might not behave as expected. “It is always dangerous to count cometary chickens before they are hatched,” Nick James, director of the comet section of the British Astronomical Association (BAA), warns in a post on the BAA website.

That’s because comets are notoriously fickle. Canadian comet hunter David Levy once said, “comets are like cats: they have tails, and they do precisely what they want.” Basically, it’s hard to predict exactly how bright a comet will be in the future.

But reports of these comets have cautiously raised astronomers’ hopes for some special sightings this fall. Here’s what to know about the pair of planetary visitors.

C/2023 A3 Tsuchinshan-ATLAS

The first of the two comets, C/2023 A3 (Tsuchinshan-ATLAS) was faintly spotted in early 2023 by the Purple Mountain Observatory in China—before it disappeared and was presumed lost, per Scientific American’s Phil Plait. A month later, however, NASA’s Asteroid Terrestrial-impact Last Alert System (ATLAS) rediscovered the celestial body and confirmed it to be a comet.

It was named C/2023 A3 (Tsuchinshan-ATLAS) in honor of both observatories, since Tsuchinshan means “purple mountain” in Mandarin. Scientists calculated the comet originated from a region called the Oort cloud in the most distant part of our solar system.

The comet was at its perihelion—the closest point to the sun in its orbit—on September 27, and it’s now passing between Earth and the sun. While it’s currently visible in the early mornings, it will soon be visible in the evenings, per Spaceweather.com. It will be closest to Earth on October 12 and may reach its peak brightness then.

Astronomers measure the brightness of celestial bodies using a stellar magnitude scale. The brighter the object, the lower the number, with negative values representing the brightest ones; inversely, the dimmer the object, the larger the positive number. Venus, for example, has a magnitude of -5, and Vega, one of the brightest stars, has a magnitude close to zero. C/2023 A3 (Tsuchinshan-ATLAS) is currently at magnitude 1.5, meaning it is a bit brighter than the North Star.

The best time to see Tsuchinshan-ATLAS, according to NASA, will be between October 14 and 24—though it will still be visible through the end of the month. Look to the west after sunset and use binoculars or a small telescope to improve your view. However, “if the comet’s tail is well-illuminated by sunlight, it could be visible to the unaided eye,” per the space agency.

Tsuchinshan-ATLAS’s close encounter with the sun vaporizes the volatile material on the comet, which creates a swell of brightness, per Space.com’s Joe Rao. The glow might be short-lived, however. The brightness of most comets coming from the Oort cloud tends to dim if not stop completely as they cross Mars’ orbit.

Thus, astronomers are cautious that C/2023 A3 (Tsuchinshan-ATLAS) may not deliver the show stargazers are hoping for. On the other hand, it still might—especially on October 14, when Earth will pass through its orbital plane and observers will see the comet’s dusty tail edge-on, which makes it brighter, per the BAA.

A ‘new sungrazing comet’

The other comet, initially designated “A11bP7I,” was just discovered on Friday by ATLAS. The recent finding has been dubbed C/2024 S1 (ATLAS), and it will likely be visible in late October or early November skies.

Currently, the comet is shining at around a magnitude 12—meaning it requires a telescope to see. But according to early predictions, the comet might become as bright as magnitude -5 to -7—potentially brighter than Venus.

A BIG NEW SUNGRAZING COMET: Today, many astronomers are excited about a new comet discovered just a few days ago by the ATLAS survey. It's so new, it doesn't have a name yet, just the provisional designation "A11bP7I." What's the excitement about? A11bP7I is a sungrazer… pic.twitter.com/BeGArf7Orv

— The Watchmen Earth and Space Connection (@TWESC2023) September 30, 2024

Still, C/2024 S1 (ATLAS) has its own set of risk factors that could affect its appearance. The comet is called a “sungrazer,” because it is a member of the Kreutz group, a family of comets that zoom exceptionally close to the sun—so close, in fact, that they either glow brilliantly or disintegrate, per EarthSky’s Kelly Kizer Whitt. In 1965, comet Ikeya–Seki was a sungrazer, and it reached a magnitude of -11—brighter than a half-illuminated moon.

“A11bP7I is at least 4-5 magnitudes fainter than Ikeya-Seki at the same distance,” Qicheng Zhang, an astronomer at the Lowell Observatory, told Spaceweather.com, per Newsweek. “Nonetheless, it could still produce a prominent visual display in early November if it survives its close encounter with the sun.” The comet’s closest approach to the sun is estimated to be October 28.

While expectations are high, stargazers shouldn’t be shocked if either (or both) comets ultimately underperform. But astronomers will be keeping their eyes on the skies to see if one of these celestial bodies becomes the “comet of the century.”

Margherita Bassi | READ MORE

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.