In a year where we’ve already been treated to the ‘Great North American Solar Eclipse’ in April and one of the greatest displays of the Northern Lights in the last 500 years in May, what other amazing celestial attractions could 2024 have in store for us? ?
How about a bright comet with the naked eye?
Over the past few years, two comets have made headlines in the mainstream media. Beginning of February 2023, Comet C/2022 E3 (ZTF)informally called the “Great Green Comet”, passed by Earth and last month, Comet 12P/Pons-Brooks attracted attention for its tendency to experience a sudden flare of brightness and appear to spout gaseous appendages that resemble horns, giving rise to the nickname ‘Devil’s Comet’.
The only problem as far as people on the street were concerned was that both comets were difficult to see unless you were under a dark, non-light-polluted sky. And even through good binoculars or a small telescope, they were both rather unimpressive and looked like nothing more than faint, dim balls 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 we will have a bright and easily visible comet in our early autumn evening sky. 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 for detecting nearby -Asteroids on Earth, a few weeks to just a few days before they could impact Earth.
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Originally thought to be an asteroid, it was later determined that the same object had been photographed six weeks earlier by the Purple Mountain Observatory (Tsuchinshan) in eastern Nanjing, China. It has since been determined that it is actually an incoming comet.
When the comet was first observed, it was far beyond the orbit of Jupiter, some 680 million miles (1.09 billion km) from the Sun. But on September 27 this year, Tsuchinshan-ATLAS will make its closest approach to the sun, at a distance of 58 million kilometers. That 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 be just 45 million miles (71 million kilometers) from Earth.
These numbers suggest the comet could brighten to second or possibly even first magnitude and develop a distinctive tail that could make a striking appearance in the western evening sky by mid-October 2024.
Read more: How to view and photograph comets
It could also be a dud
Unfortunately, there’s a caveat: Calculations show that Tsuchinshan-ATLAS has an orbital eccentricity of 1.0001081, meaning it’s a “first-timer,” coming straight from the Oort Cloud, a spherical shell of icy space debris that scientists theorize that it is located far beyond the outer limits of the solar system and probably billions or even trillions of comets.
Comets originating from the Oort Cloud have never come close to the Sun before, and their nuclei are coated with highly volatile materials that evaporate far from the Sun, creating short-lived brightness spikes. But as these comets get closer to the Sun, their brightening slows or even stops altogether.
Most – but admittedly not all – comets that emerge from the Oort Cloud usually end up as duds. When these comets cross the orbit of Mars, their steady brightening trend begins to falter, much like a marathon runner’s 20-mile run; ‘hitting the wall’, so to speak. In the event that a comet emerges from the Oort cloud, a sudden decrease in brightness could be a signal that the comet will eventually underperform.
Not until mid-summer
Comet Tsuchinshan-ATLAS won’t reach that point in its orbit until late July. If it continues to brighten steadily after that time, chances are it will grow into a striking sight. But it is more likely that if the uptrend suddenly slows down or even comes to a halt, all chances of a good show are eliminated. Until then, all we can do is wait and watch.
Unfortunately, here in the Northern Hemisphere we will not be able to check the status of comet Tsuchinshan-ATLAS this summer, as it will be much too far south to be reachable with telescopes. However, those living in far southern locations such as Australia, New Zealand and South America will be able to watch it before sunrise in the morning sky.
We will have to rely on reports from these parts of the world to tell us whether the comet is on its way to potentially becoming a bright object.
Dusty reflections are the key to a good show
Something else that could 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 ‘forward scattering of sunlight’. If the comet is particularly dusty, dust grains ejected from the comet’s nucleus will preferentially scatter sunlight forward, which can cause a dramatic increase in the comet’s brightness.
In view of this, 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 X1), which briefly became very bright in December 1927. The forward scatter of light on December 18, 1927 allowed the comet to be seen in daylight by blocking the light from the Sun. manual; it has since been ranked as one of the 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 more than 40 years; easily visible with 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 in wide areas worldwide . daylight next to the sun. This extreme brightness was also due to forward scatter.
Some calculations suggest that Tsuchinshan-ATLAS could become as brilliant as Venus around October 8, 2024 – although like the comets of 1927 and 2007, it will also be very close to the Sun’s position in the sky. However, in the days that follow, Tsuchinshan-ATLAS should move quickly northward and be well positioned to be observed 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 easily visible to the naked eye, perhaps also accompanied by a distinctive tail.
No guarantees
But there are no guarantees. In the past, there have been comets that seemingly promised a great show that 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 were doing well, but ended up unexpectedly becoming celestial showpieces. Comet NEOWISE surprised everyone during 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 have to 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 an instructor and guest lecturer in New York Hayden Planetarium. He prescribes on astronomy Natural history magazinethe Farmer’s almanac and other publications.