THE brightest comet in Australia's skies for more than 40 years will be visible from Jan 15th, astronomers have said.

Dr James Biggs, director of the Perth Observatory, said the McNaught Comet is currently at its closest approach around the Sun and will be visible to West Australians from Monday 15th for about a week.

"It should be easy to locate. Find a vantage point with an unobstructed view and look low on the horizon near where the Sun has set, in the direction of south-west, around 9pm (WDT)," Dr Biggs said.

The 10km wide comet was discovered by Australian astronomer Rob McNaught at Siding Spring Observatory, in NSW, in August 2006.

Dr Biggs said it was 12 per cent brighter than the sighting in 1995 of the Hale-Bopp Comet but still 25 times fainter than 1965's Ikeya-Seki Comet.

"But we don't get to see its true brightness because it's close to the Sun and obscured by twilight," he said.

Northern Hemisphere observers have reported the tail of dust cloud following the comet is especially impressive when viewed through binoculars.

The tail is created when the Sun's radiation turns ice on the comet's outer surface to water vapour, releasing dust particles.

Observers are reminded, because of the comet's closeness to the Sun, never to look directly at the Sun with the naked eye or through an optical instrument.