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Comet ISON: welcome, stranger

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Perry Vlahos

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Telling tail: Some comets are quite spectacular.

Telling tail: Some comets are quite spectacular.

A year ago this Saturday, a couple of Russian astronomers using a 40.6-centimetre telescope of the International Scientific Optical Network (ISON) made an unexpected discovery. Usually on the lookout for asteroids, its camera captured something else in deep space heading towards the inner solar system. It was soon confirmed to be a comet and was named Comet ISON.

Refinement of its orbit by astronomers added to the excitement; this comet will get very close to the sun this spring and could become a spectacular object to behold with naked eye in late November in our pre-dawn skies, if it survives its encounter with Sol.

Much publicity was generated, and it even acquired the tag ''Comet of the Century''. I fear this might be a little premature as comets can be very unpredictable. Most experienced comet observers who weren't sipping the celebratory Bollinger at its discovery also advised caution.

More excitement ensued when it was established that its path would carry it close to Mars on October 1 - passing within a few million kilometres.

We're not certain of the size of its nucleus as it's shrouded in dust and ice. But how large the core is will be an important factor in determining whether ISON survives its journey around the sun and how impressive a sight it becomes for us on Earth. The Martian encounter will provide an opportunity to gain knowledge on that front as we have instruments in the Martian orbit or on the ground that are capable of examining it.

NASA's Mars Reconnaissance Orbiter, equipped with a half-metre telescope, is best placed to give us the skinny on this icy visitor. Once that information is relayed to Earth, we'll have a better idea of how Comet ISON will perform in a couple of months.

An introductory course on astronomy will be run for the public by Perry Vlahos next month. For details, email perryv@optusnet.com.au.