What other amazing celestial attractions might 2024 hold in a year where we already saw the “Great North American Solar Eclipse” in April and one of the largest Northern Lights displays in the last 500 years in May? ?
How about a bright comet that is visible to the naked eye?
In recent 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,” it passed Earth and then last month Comet 12P/Pons-Brooks attracted attention because it tended to experience sudden increases in brightness and eject gaseous appendages that resembled horns, earning it the nickname “Devil’s Comet.”
The only problem for the person on the street 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 rather faint, appearing only as faint, blurry blobs of light.
Related: 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 whether a bright and easily visible comet will grace our early fall evening skies. The comet in question is C/2023 A3 (Tsuchinshan–ATLAS), which was discovered on February 22, 2023 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in South Africa. ATLAS is a robotic early warning system designed specifically to detect near-Earth asteroids several weeks to a few days before they could hit Earth.
It was originally thought to be an asteroid, but it was later discovered that the same object had been photographed six weeks earlier by the Purple Mountain Observatory (Tsuchinshan), east of Nanjing, China. It has since been determined that it is actually an incoming comet.
When the comet was first spotted, it was well outside Jupiter’s orbit, about 680 million miles (1.09 billion kilometers) from the sun. But on September 27 this year, Tsuchinshan-ATLAS will come closest to the Sun, coming within 36 million miles (58 million km). This is also 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 71 million kilometers from Earth.
These numbers suggest that the comet could brighten to second or possibly even first magnitude and develop a notable tail that could make for a striking sight in the western evening sky in mid-October 2024.
Read more: How to observe and photograph comets
It could also be a dud
Unfortunately, there is a caveat: calculations show that Tsuchinshan-ATLAS has an orbital eccentricity of 1.0001081, meaning it is a “maiden flight” coming directly from the Oort cloud, a spherical shell of icy Space debris that scientists suspect is located far beyond the outer limits of the solar system and is thought to contain billions or even trillions of comets.
Comets that originate from the Oort Cloud have never passed close to the Sun before, and their nuclei are coated in highly volatile materials that evaporate far from the Sun, producing short-term bursts of brightness. But as these comets get closer to the Sun, their brightening slows down or even stops altogether.
Most – although admittedly not all – comets that come from the Oort cloud usually turn out to be duds. When these comets cross Mars’ orbit, their steady trend in brightness typically stalls, similar to a marathon runner at the 20-mile mark; he “hits the wall,” so to speak. In the case of a comet that emerged from the Oort cloud, a sudden drop in brightness can be an indication that it will ultimately no longer perform as expected.
Only in midsummer
Comet Tsuchinshan–ATLAS will not reach this point in its orbit until the end of July. Then, if it gets steadily brighter beyond that period, there’s a good chance it will become a striking sight. But more likely, if the brightening trend suddenly slows or even stops, all bets on a good show are off. 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 as it is far too far south to be accessible by telescope. However, those living in much more southerly locations such as Australia, New Zealand and South America will be able to track it in the morning sky before sunrise.
We must rely on reports from these parts of the Earth to know whether the comet is on track to potentially become a bright object.
Dusty reflections are the key to a good show
Another point that could work in our favor is the geometry of the comet in relation to the Sun and the Earth, which places it almost between the Sun and the Earth around October 8th, creating a phenomenon called “forward scattering of sunlight “ is known. If the comet is particularly dusty, the dust particles ejected from the comet nucleus would preferentially scatter sunlight forward and could cause a dramatic increase in the comet’s brightness.
To this end, there are two comets that Tsuchinshan-ATLAS could be compared to, which suddenly became brighter thanks to forward scattering. The first was comet Skjellerup-Maristany (C/1927 by hand; it has since been classified as one the largest comets of all time.
The other comet was Comet McNaught, also known as the Great Comet of 2007 and designated C/2006 P1, was the brightest comet in over 40 years; It was clearly visible to the naked eye to observers in the southern hemisphere in 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 worldwide in wide daylight next to the Sun. This extreme brightness was also due to forward scattering.
Some calculations suggest that Tsuchinshan-ATLAS could become as bright as Venus around October 8, 2024 – although it will also be very close to the position of the Sun in the sky, like the comets of 1927 and 2007. However, in the following days, Tsuchinshan–ATLAS is expected to move quickly north and be in a good position for observation in the western sky by mid-October. Although it is now fading as it moves away from both the Sun and Earth, it will hopefully be bright enough to be clearly seen with the naked eye, possibly accompanied by a notable tail.
No guarantees
But there are no guarantees. In the past, there have been comets that seemed to promise a great show but failed to live up to 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 that unexpectedly turned into celestial showpieces. Comet NEOWISE surprised everyone with a good show in summer 2020.
The 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, we keep our fingers crossed for comet Tsuchinshan–ATLAS! Stay tuned to Space.com for future updates.
Joe Rao is a lecturer and visiting professor at New York University Hayden PlanetariumHe writes about astronomy for Journal of Natural HistoryThe Farmers Almanac and other publications.