• WHERE THEY COME FROM • HOW THEY SPARK LIFE
• THIS YEAR’S UNMISSABLE EVENTS
• MAKE YOUR OWN DISCOVERY
A comet bright enough to be seen with the naked eye is one of the most fascinating and thrilling sights in astronomy, and the appearance of a great comet, with a bright head and glowing tail, is a very rare event indeed. The last great comet to grace our skies was comet Hale-Bopp in 1997. That beautiful twin-tailed comet was seen by millions around the world, but that world was very different to the one we live in today. The internet was still young, and social media had yet to be born. There were no computerised telescopes, no astronomy phone apps, no fancy CCD cameras or stacking of images.In many ways Hale-Bopp was the last great comet of the pre-digital age. Next autumn, Comet C/2023 A3 Tsuchinshan-ATLAS might be the brightest comet in the sky since Comet Hale-Bopp. If it lives up to expectations, we might see the return of old-fashioned ‘comet fever’ as reports of the comet’s appearance and thousands of breathtaking digital images of it flood social media. If it falls short, astronomers might face a level of disappointment and anger not seen since Comet ISON – predicted to be the comet of the century – sputtered out and fell to pieces back in 2013. So now is a good time to take a deep breath and take a look at comets – what we used to think about them, what we know about them now and how to observe them – and take an early look at what we might see in the sky at the end of next year.
WHAT ARE COMETS?
We once believed that comets were strange, vaporous objects that trailed through Earth’s atmosphere, or flaming rocks from the depths of space that passed by our planet. Today, after centuries of observation and research, we know that comets are among the most ancient bodies in our Solar System. We know they are icy bodies that contain large amounts of dust and gas. They are members of the Solar System, just like the planets, but while the orbits of the planets are roughly circular, comets’ orbits are much more eccentric, so they spend most of their time far away from the Sun and only come near it for a small part of their orbit. Some comets take only a few years to go around the Sun, while others take hundreds, thousands or even tens of thousands to orbit it.
The solid part of a comet is called the nucleus. It is a very dark, icy body, almost like a huge charcoal briquette tumbling through space. Comets only show themselves when they get close enough to the Sun for its heat to thaw them out enough to release some of the dust and gas from the nucleus. This forms a glowing cloud, or ‘coma’, around
