Hive’s principal astronomer, Dr Martin George, has been busy with comets in recent times!
In October, Comet Tsuchinshan-ATLAS was visible in our evening sky in the late twilight, and just after mid-January, so was Comet ATLAS. October’s comet was discovered in 2023, jointly by the Purple Mountain Observatory in China (Tsuchinshan), and the South African telescope of the Asteroid Terrestrial-impact Last Alert System (ATLAS). January’s comet – first seen in 2024 –was purely an ATLAS discovery.
Unfortunately, neither became as bright as some people had hoped; each was just visible with the unaided eye for a short period before they faded. However, binoculars were a great help and offered a fine view of both the head and tail of January’s comet. Comets have been likened to ‘dirty snowballs’, made up of different ices – including water – and particulate material. They are quite loosely held together and have been known to break apart. Indeed, this was the worry about the more recent of the two comets, which, during January, passed closer to the Sun than the innermost planet, Mercury.
Comets’ tails are formed when near the Sun, as the Sun’s energy removes cometary material to form a tail pointing generally away from the Sun. Photographs of comets can make them look a lot more impressive than the view with the unaided eye. This is because when the CCD sensor (or film) is exposed to the image of the comet – the image formed by the camera lens – the image ‘builds up’ on the sensor, continually adding to how bright the comet (and stars, too) appear on the image. So the recent comets look a look more prominent through imaging.
We shan’t see these comets again; they are on very elongated orbits that take them a very great distance from the Sun before they can ever begin a return journey. Comet Tsuchinshan-ATLAS may never return, but Comet ATLAS could be back in the inner Solar System after another several hundred thousand years.
Neither of these comets was nearly as bright as Comet Hyakutake (1996), Comet Hale-Bopp (1997) or the magnificent Comet McNaught (2007), but now and again, as was the case with those three comets, one is discovered on a rare (or first) visit to our part of the Solar System and becomes a fine sight with the unaided eye.