The changing appearance of planets in the sky is generally predictable. But occasional celestial visitors called comets can spring a surprise.
These are icy chunks of debris left over from the formation of the Solar System, Much smaller than planets or moons, they travel in highgly elongated orbits from deep space to the inner Solar System .
Many are known that orbit in just a few years and so their return appearances are entirely predictable. The best known of these is Halley’s Comet which returns every 76 years – unfortunately it is not next due until around 2061!
Other comets can take astronomers completely by surprise if they are making their first recognised visit to the inner Solar System from an icy zone called the Oort Cloud, which exists far beyond the outer planets.
These unexpected visitors can become very bright and produce long tails of gas and dust as they are warmed by the Sun. Examples in recent times have included Comet Hale-Bopp in 1997 and Comet McNaught in 2007.
A small number of comets can be seen with binoculars each year. Whether they appear as faint, ghostly objects or become bright with long tails to the unaided eye, the SPA will help you with advice on how to observe and even photograph them.