Caption for new AAO colour picture of Comet Hyakutake

Comet Hyakutake was discovered by a Japanese amateur astronomer on 30 January, 1996, and it was soon realised that its orbit would bring it within 15 million kilometers of the earth, about one-tenth the earth-sun distance. It would therefore be the closest bright comet for 450 years. The comet has recently been visible to the unaided eye and has been a spectacular sight in Australia's northern sky in the early hours of the morning for the last week or so. Unfortunately for those of us in the southern hemisphere, the comet was moving rapidly northwards and was invisible from most of Australia when it was at its closest, on March 25.

However, the UK Schmidt telescope had the opportunity to photograph this fleeting visitor on the night of March 18-19 and a new 3-colour picture is the result. This specially enhanced picture reveals a very faint multicoloured tail, which points away from the sun. It is made of dust and gas evaporated from the comet's nucleus by sunlight and this image shows a surprising range of subtle colours, probably the result of changes in the tail during the series of exposures, which took about an hour. The brilliant blue coma around the head of the comet is also the result of sunlight, exciting molecules which have been evaporated from the comet's icy nucleus. The nucleus itself is very small, only a few tens of kilometers in diameter, but the tenuous coma is millions of kilometers across.

This photograph of Comet Hyakutake 1996 B2 was made with the Anglo-Australian Observatory's UK Schmidt Telescope at Siding Spring, Australia. Three separate exposures of about 15 minutes were made in the order green, red, blue as the telescope followed the comet. This accounts for the coloured star trails, elongated by the rapid northerly movement. Hypersensitised Tech Pan film was used and the exposures were made by Ken Russell and Dione James on the night of 18-19 March, 1996. The 3-colour picture was made by David Malin of the Anglo-Australian Observatory. This photograph is copyright Anglo-Australian Observatory.

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