Image Credit : ESO/E. Slawik

If I asked you to name the most famous comet, I would put my money on you replying “Halley’s Comet.” Comets are huge lumps of dust, rock, gas and ice that exist in the massive Oort Cloud in the outer reaches of our solar system way out past Pluto. Some of these objects are gradually pulled in by the Sun’s gravity and, according to NASA, the number of known comets is 3,743, but it’s thought there are billions orbiting the Sun in total. As they get closer to our star, they heat up and spew material for millions of miles out into space behind them, leaving their trademark tails, a white one of dust and a blue one of ions but always pointing away from the Sun. The word Comet is from the Greek “cometes” meaning “hairy star”. Some comets are pulled in and if they are not broken up by the Sun’s gravity and heat they whip around and exit the solar system permanently, rather than remaining in an elliptical orbit.

So why “Halley’s Comet”? In 1705 the astronomer Edmond Halley noticed three comets with strikingly similar orbits, seen in 1531, 1607, and 1682. He concluded that they were actually the same comet, passing by every 76 years, and he predicted it would appear again in 1758 but didn’t live to see it. Because of this scientific discovery this comet was named after him. Comets were often seen as omens either for good or ill. Halley’s Comet previously appeared in 1066 and is shown in the Bayeux Tapestry. Good for conquering William, but one in the eye for Harold. From Rosenannon I have so far observed 9 comets, most being small fuzzy green blobs but my first observable comet was in April 1997 with Comet Hale Bopp as shown here above my field with the setting Moon. This was most spectacular with its rocky 19 mile diameter green glowing nucleus trailing two tails, one of blue ionized gas and the other made of dust glowing white by the sunlight. You may have seen the recent Comet Neowise in July 2020 that put on a beautiful show firstly in the morning sky and then in the evening sky as it moved around the Sun.

Halley’s Comet 76 year regular reappearance means it could be seen twice in one person’s lifetime. It last appeared in 1986 putting on a disappointing show but the European spacecraft Giotto became one of the first spacecraft to encounter and photograph the nucleus of a comet, passing and imaging Halley’s 3.4 mile wide nucleus as it receded from the Sun. Last December 9th it had reached its farthest turning point over 3 billion miles out past Neptune and is now heading back towards the Sun and will next appear in our sky in 2061. I will then be 104 so I might see it but I wouldn’t put money on it!! 

By Glynn Bennallick