Celestial body could become brighter than the stars

 A comet approaching Earth to shine brighter than stars this fall  

In a year in which we have already been treated to the "Great North American Solar Eclipse" in April and one of the greatest displays of Northern Lights in the past 500 years in May. Here is good news for skywatchers as they have a cosmic treat this autumn. Comet approaching earth this autumn could outshine stars in a spectacular celestial display. A comet approaching the earth will be visible with more shine than the stars. Known as C/2023 A3 (Tsuchinshan–ATLAS), this comet was spotted by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in South Africa on February 22, 2023. Tsuchinshan–ATLAS might become as brilliant as Venus. Astronomer Gianluca Masi of the Virtual Telescope Project also captured this Comet C/2023 A3 Tsunchinshan-ATLAS on May 5, 2024 from Ceccano, Italy. 

Over the last couple of 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 near Earth and then during the past month, Comet 12P/Pons-Brooks drew attention because of its propensity for experiencing sudden flare-up in brightness and appearing to spout gaseous appendages resembling horns, thus giving rise to the moniker "Devil's Comet."  The only problem so far as the person-on-the-street was concerned was that both comets were difficult to see unless you were located under a dark, non-light polluted sky. And even through good binoculars or a small telescope, both were rather unimpressive, appearing as nothing more than faint, fuzzy blobs of light. But by the end of this summer, we may have a good idea as to whether we'll have a bright and easy-to-see naked-eye comet gracing our early autumn evening sky. The comet in question is C/2023 A3 (Tsuchinshan–ATLAS). ATLAS is a robotic early warning system developed specifically for detecting near-Earth asteroids a few weeks to just days before they might impact Earth. 

Initially, scientists believed it was an asteroid, but later observations from the Purple Mountain Observatory in China confirmed it as a comet. When it was first spotted, the comet was beyond Jupiter’s orbit, about 680 million miles(1.09 billion km)  from the Sun. But on September 27, this year, Tsuchinshan–ATLAS is expected to come closest to the Sun. It will pass at a mere 36 million miles(58 million km). That also happens to be the average distance of the planet that is closest to the sun, Mercury. This is almost as close as Mercury's usual distance. Then, just over two weeks later, on October 12, 2024, it'll pass within 44 million miles of Earth. These figures suggest that the comet might brighten to second or possibly even first magnitude and could develop a notable tail that could make for an eye-catching sight in the western evening sky during mid-October 2024.

Tsuchinshan–ATLAS might become as brilliant as Venus. Unfortunately, there is a caveat: calculations show that Tsuchinshan–ATLAS has an orbital eccentricity of 1.0001081, meaning that it is a "first-timer," coming directly from the Oort cloud, a spherical shell of icy space debris scientists theorize to be situated far beyond the outer limits of the solar system and thought to contain billions or even trillions of comets. Comets originating from the Oort cloud have never passed near to the sun before and their nuclei are coated with very volatile materials that vaporize far from the sun, creating short-lived surges in brightness. But as these comets get nearer to the sun, their brightening slows or even stops completely. Not all, but mostly comets originating from the Oort cloud usually end up being duds. Typically, as these comets cross the orbit of Mars, their steady brightening trend starts to falter, similar to a marathon runner at the 20-mile mark; "hitting the wall" so to speak. In the case of a comet having emerged from the Oort cloud, a sudden decline in brightening may be signaling that it ultimately will end up underperforming.  Not until mid-summer.

Comet Tsuchinshan–ATLAS will not get to that point in its orbit until late July. If it then continues to steadily brighten beyond that time, then there's a good chance it will evolve into an eye-catching sight. Unfortunately, we here in the Northern Hemisphere will not be able to check on the status of Comet Tsuchinshan–ATLAS during this summer because it will be situated much too far south to be accessible with telescopes. Those living in far-southerly locations, such as Australia, New Zealand and South America, however, will be able to track it in the morning sky before sunrise. But, more likely, if its brightening trend suddenly slows, or even comes to halt, all bets for a good show are off. Until then, all we can do is wait and watch.

To this end, there are two comets that Tsuchinshan–ATLAS might be compared to, which suddenly brightened-up thanks to forward scattering. The first was Comet Skjellerup–Maristany (C/1927 X1), which briefly became very bright in December 1927. Forward scattering of light on Dec. 18, 1927 allowed the comet to be seen during daylight by virtue of blocking the light of the sun with one's hand; it has since been ranked as among the greatest comets of all time. The other comet was Comet McNaught, also known as the Great Comet of 2007 and given the designation C/2006 P1, and was the brightest comet in over 40 years; easily visible to the naked eye for observers in the Southern Hemisphere in January and February 2007. At its brightest on 12 Jan, 2007, this comet appeared at least twice as bright as Venus and, like Skjellerup–Maristany, was visible worldwide in broad daylight next to the sun. This extreme brightness was also attributable to forward-scattering. 

We'll need to rely on reports from these parts of the globe to tell us whether the comet is on track to possibly becoming a bright object.  Dusty reflections hold key to a good show. Another thing that could work in our favour is that the geometry of the comet relative to the sun and Earth, places it almost in-between the sun and Earth around Oct. 8, creating a phenomenon known as "forward scattering of sunlight." If the comet is particularly dusty, dust particles ejected from the comet nucleus would preferentially scatter sunlight in a forward direction and could cause a dramatic upsurge in the comet's brightness. Some calculations suggest that Tsuchinshan–ATLAS might become as brilliant as Venus around Oct. 8, 2024, although in the sky, like the comets of 1927 and 2007, it will also be very near to the position of the sun. In the days that follow, however, Tsuchinshan–ATLAS should sweep rapidly northward and become well-placed for viewing in the western sky by mid-October. Although it will now be fading as it recedes from both the sun and Earth, it hopefully will be bright enough to be well-seen with the naked-eye, perhaps accompanied by a notable tail as well.  

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 of 1973-74 is a good example. Conversely, there have been comets that did not look like they would perform well, that ended up unexpectedly becoming celestial showpieces. Comet NEOWISE surprised everyone during the summer of 2020 by putting on a good show. 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!""

Astronomers think that these close encounters could make the comet brighten up to become as radiant as some of the brightest stars, possibly even developing a striking tail. If all goes according to plan, by mid-October, it could be an eye-catching sight in the evening sky out west. If the predictions pan out, it would be a truly breath taking spectacle for stargazers. There is the possibility that Tsuchinshan–ATLAS might become as brilliant as Venus on October 8, 2024, according to some calculations. It will start fading as it recedes from both the sun and Earth. However, it hopefully will be bright enough to be seen with the naked eye.