In a year where we’ve already been treated to the Great North American Solar Eclipse in April and one of the biggest displays of the Northern Lights in 500 years in May, what other amazing celestial attractions might 2024 have in store?
How about a bright comet with the naked eye?
In the past few years, two comets have made headlines in the mainstream media. In early February 2023. Comet C/2022 E3 (ZTF)informally called the Great Green Comet, passed close to Earth and then in the past month, Comet 12P/Ponce-Brooks attracted attention for its propensity for sudden bursts of brightness and appearing to emit gaseous horn-like appendages, giving rise to the nickname “Devil’s Comet”.
The only problem, as far as the man in the street was concerned, was that both comets were difficult to see unless you were under a dark, unpolluted sky. And even through good binoculars or a small telescope, both were pretty unimpressive, looking like nothing more than faint, fuzzy patches of light.
Connected: A comet coming in 2024 could outshine the stars – if we’re lucky
Bright? Easy to see?
But by the end of this summer, we may have a good idea if we’ll have a bright and easy-to-see-with-the-unaided-eye comet gracing our early fall evening skies. The comet in question is C/2023 A3 (Tsuchinshan–ATLAS), discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in South Africa on February 22, 2023. ATLAS is a robotic early-warning system developed specifically to detect near-Earths. asteroids a few weeks to just days before they hit Earth.
Originally thought to be an asteroid, this same object was later found to have been imaged six weeks earlier by the Purple Mountain (Tsuchinshan) Observatory in eastern Nanjing, China. It has since been determined to actually be an approaching comet.
When the comet was first spotted, it was well beyond the orbit of Jupiter, about 680 million miles (1.09 billion kilometers) from the sun. But on September 27 this year, Tsuchinshan-ATLAS will make its closest approach to the sun, reaching 36 million miles (58 million km). This also happens to be the average distance of the planet closest to the sun, Mercury.
And just over two weeks later, on October 12, the comet will pass just 44 million miles (71 million kilometers) from Earth.
These numbers suggest that the comet could brighten to second or possibly even first magnitude and could develop a remarkable tail that could make for an eye-catching sight in the western evening sky in mid-October 2024.
Read more: How to watch and photograph comets
It might as well be bullshit
Unfortunately, there’s one caveat: calculations show that Tsuchinshan–ATLAS has an orbital eccentricity of 1.0001081, meaning it’s a “first-ever” coming directly from the Oort cloud, a spherical shell of icy space debris that scientists theorize that lies far beyond the outer limits of the Solar System and is believed to contain billions or even trillions of comets.
Comets originating from the Oort cloud have never passed close to the sun before, and their nuclei are covered in highly volatile materials that evaporate away from the sun, creating short-lived peaks of brightness. But as these comets approach the sun, their brightness slows or even stops altogether.
Most – though not all – comets that originate in the Oort cloud tend to turn out to be duds. Usually, when these comets cross the orbit of Mars, their steady trend in brightness begins to fluctuate, much like a marathon runner at 20 miles; “hitting the wall” so to speak. In the case of a comet emerging from the Oort cloud, a sudden drop in brightness may be a signal that it will eventually fail.
Even in the middle of summer
Comet Tsuchinshan–ATLAS will not reach this point in its orbit until late July. If it then continues to glow steadily after that time, then there is a good chance it will become an eye-catching sight. But more likely, if his tendency to lighten suddenly slows down or even stops, all bets are off for a good show. Until then, all we can do is wait and watch.
Unfortunately, we here in the Northern Hemisphere will not be able to check the status of Comet Tsuchinshan–ATLAS this summer because it will be located too far south to be accessible by telescopes. However, those living in far southern locations such as Australia, New Zealand and South America will be able to track it in the morning sky before sunrise.
We will have to rely on reports from these parts of the globe to tell us if the comet is about to become a bright object.
Dust reflections are the key to a good show
Another thing that may work in our favor is that the comet’s geometry relative to the sun and Earth puts it almost between the sun and Earth around October 8, creating a phenomenon known as “scattering sunlight.” If the comet is particularly dusty, dust particles ejected from the comet’s nucleus would preferentially scatter sunlight in a forward direction and could cause a dramatic spike in the comet’s brightness.
To this end, there are two comets with which Tsuchinshan–ATLAS can be compared, which suddenly brightened due to forward scattering. The first was Comet Skjellerup–Maristany (C/1927 X1), which briefly became very bright in December 1927. Forward light scattering on December 18, 1927 allowed the comet to be seen during the day, due to its arm blocking sunlight ; since then it has been ranked as mid the greatest comets of all time.
The other comet was Comet McNaught, also known as the Great Comet of 2007 and designated C/2006 P1, and was the brightest comet in over 40 years; easily visible to the naked eye to observers in the southern hemisphere during January and February 2007. At its brightest on January 12, 2007, this comet appeared at least twice as bright as Venus and, like Skjellerup-Maristany, was visible around the world in broad daylight to the sun. This extraordinary brightness is also due to forward scattering.
Some calculations suggest that Tsuchinshan–ATLAS may become as bright as Venus around October 8, 2024 – although in the sky – like the 1927 and 2007 comets – it will also be very close to the sun’s position. In the coming days, however, Tsuchinshan–ATLAS should move rapidly northward and become well positioned for viewing in the western sky by mid-October. Although it will now fade as it moves away from both the sun and Earth, it will hopefully be bright enough to be clearly visible to the naked eye, perhaps accompanied by a prominent tail.
No guarantees
But there are no guarantees. In the past, there have been Comets that seemingly promised a great show that fell short of expectations. Comet Kohoutek from 1973-74 is a good example. Conversely, there have been comets that didn’t look like they would perform well, but unexpectedly turned into celestial exhibits. Comet NEOWISE surprised everyone in the summer of 2020 by putting on a good show.
Legendary comet expert Dr. Fred Whipple perhaps said it best when he said:
“If you must bet, bet on a horse, not a comet!”
In the meantime, fingers crossed for Comet Tsuchinshan–ATLAS! Stay tuned to Space.com for future updates.
Joe Rao serves as an instructor and guest speaker in New York Hayden Planetarium. He writes about astronomy Journal of Natural History.on Farmer’s Almanac and other publications.
