Comets are dirty snowballs, mixtures of ice and dust. They are deep-frozen time capsules that preserve a record of conditions during the formation of the Solar System about 4.5 billion years ago. Billions of them are thought to orbit the Sun in a gigantic spherical cloud (known as the Oort Cloud, after the 20th century Dutch astronomer Jan Oort) beyond the orbit of Pluto. Gravitational perturbations sometimes disturb a comet, causing it to fall in towards the Sun. As it gets closer to the Sun, it gradually develops a tail of evaporating debris, which slowly disappears again as it returns to the region from which it came. The brighter and closer comets are visible from Earth.
In most years, we never see a comet. But in 2013, we are probably going to be lucky enough to see three of them. Although we know their orbits very accurately, predicting their likely brightness is extremely difficult. But it is possible that the last of these three (comet ISON, arriving late November) may be a truly spectacular one.
The first comet of the year (comet Pan-STARRS) will appear in the skies of South Devon in mid-March. Look out for it low on the western horizon just after sunset on and after Tuesday, March 12. It should be clearly visible with the unaided eye.
The photo that accompanies this article is of comet Hale Bopp, which appeared in 1997. It was taken by Simon Harding, who is probably the best astro-photographer in Devon.
The Torbay Astronomical Society will be meeting twice this month, at Torquay Boys’ Grammar School in Shiphay Manor Drive. Our next observing evening will be on Thursday 14 March. If the skies are clear, it will give us a chance to see comet Pan-STARRS. But the comet sets early, so if it’s a clear sky and if you want to see the comet, please arrive at about 7pm, rather than 7.30pm. If it’s cloudy or if you don’t want to see the comet, then please arrive at the usual time of 7.30pm. In the event of a cloudy evening, Simon Harding will be explaining how he takes his astro-photographs.
One week later, on Thursday, March 21, we shall be having our quiz against the North Devon Astronomical Society. The quiz will be chaired by Keith Ball, Dennis Humphreys will keep the score, and the Torbay team will consist of Dave Norman, Simon Harding, Andrew Sellek and A N Other. Do please come along.
Visitors and new members are always welcome. There is a £3 charge for visitors to the lecture evenings, and a £2 charge for the observational evenings. Annual membership is a mere £15 (reduced to £10 for senior citizens).