By james art By Isabella Castel-Branco
“Comet of the Century”, “Last Seen by Neanderthals”, … many such claims regarding Comet Tsuchinshan–ATLAS are currently flooding the news platforms as it reappeared visible in the twilight sky. Although it is not the only one in recent times, it has attracted wide attention due to its promising features.
In everyday language, terms like comets, asteroids, and meteors are often used interchangeably, as if they were all just space rocks. However, each category is clearly defined, and understanding these differences helps explain why comets are in particular demand. Asteroids are space rocks ranging from a dozen meters to hundreds of kilometers in diameter. These irregularly shaped objects orbit the Sun, mainly in the asteroid belts between Mars and Jupiter and extending beyond Neptune. In contrast, meteoroids are smaller pebble-sized space rocks—often fragments of asteroids. When these meteoroids burn up in the Earth’s atmosphere, they become meteors, and any surviving fragments that reach the Earth’s surface are called meteorites. These objects are categorized based on size and position. Comets vary in composition; their cores are usually made of ice and dust, giving them a distinctive elongated, blurry appearance.
Comets usually have two distinct tails: the longer, notorious tail that gave them their name from the Greek komētēs (a star with long hairs), consists of evaporating ice and dust. The second, the ion tail, is caused by powerful solar winds and is directed directly away from the Sun as electrically charged particles are torn off the surface and ejected into space. The ion tail is bright and colorful, usually blue. Both tails stretch for millions of kilometers. As comets travel through the solar system, they create spectacular shows on Earth; the debris they leave behind is encountered by Earth during its orbit, resulting in annual meteor showers as we pass through the comet’s remains. Comets are particularly interesting objects to study because they are remnants of the formation of the Solar System and therefore could give us further clues about its past evolution.
As first proposed by Edmund Halley, comets may be periodic: that is, they may return every certain number of years after completing a long orbit around the Sun. The Solar System is theorized to be surrounded by the Oort Cloud, a vast reservoir of small rocky objects potentially harboring billions of comets. This would explain how we regularly have such visitors — the most recent and memorable for our generation was Neowise in 2020, but we’ve had a few less notable ones since. If Tsuchinshan–ATLAS is indeed a periodic comet, it is believed to have last passed by Earth 80,000 years ago, when Neanderthals were still alive.
It is estimated that it last passed Earth 80,000 years ago, when Neanderthals were still alive
As it approaches the Sun, Tsuchinshan–ATLAS is visible to the naked eye. Observed instrumentally since its discovery in January 2023, it has only two brief viewing windows: just before and after its closest approach to the Sun (perihelia), when it shines brightest, illuminated by sunlight reflecting off the icy its surface. The first, from Sept. 27 to Oct. 2, is visible in the east just before sunrise, and the current one, from Oct. 12 to 30, is visible in the west just after sunset, according to the Royal Astronomical Society. So far, it has been named “comet of the year” due to its peak apparent magnitude of -4. The more negative the magnitude, the brighter the object: the faintest objects we can see are at apparent magnitude +6, while the Sun is approximately at apparent magnitude -26. However, being so close to the Sun places limits on observation. Although it is brighter when it is closer, it rises and sets with the day, making it difficult to see before disappearing below the horizon.
The comet is not yet easily seen in Durham, as it is too close to the horizon when the Sun sets and is therefore hidden by hills and trees. However, each day, it will reach a higher altitude (but also become weaker). With an updated map of the sky, a clear view of the western horizon and a pair of binoculars, amateur astronomers should find it a rewarding subject to pursue. I wish clear skies to all who try!
Image by James Peirce via Flickr
