Western Australian star-gazers have been treated to a unique astronomic event at dusk with a brief 'face-off' from opposite horizons between the sun and the moon.

Speaking before the phenomenon, University of Western Australia physics professor David Blair told 720 ABC Perth that at the same time the moon rose in east, the sun would be touching the horizon in the west.

"You really get the sense of the Earth turning, with the moon popping above the horizon and the sun sitting there, touching the western edge of the horizon," he said.

The face-off occured at 6:25pm (AWST) on Tuesday evening.

However overcast conditions in Perth appear to have hampered views of the sun and moon.

The occurance also coincided with a supermoon, which made the moon appear 14 per cent larger than usual.

"That's a pretty rare event, I haven't seen one with such perfect timing in quite a few years," Professor Blair said.

A supermoon is a new or full moon closely coinciding with perigree — the moon's closest point to Earth in its orbit.

"The moon looks bigger and smaller at different times because the moon gets closer to us at different times of the month in its elliptical cycle," Professor Blair said.

The face-off was not visible in other parts of Australia.

In Sydney, the sun and moon were set to miss each other by 18 minutes, but in Perth the moonrise and sunset coincidence would have been "spot on", according to Professor Blair.

Public astronomy centre opens for face-off

Gravity Discovery Centre at Gingin with the observatory and leaning observation tower will open tonight with new telescopes. ( Supplied: Gravity Discovery Centre )

Professor Blair is a co-founder of the Gravity Discovery Centre (GDC) at Gingin, 90 kilometres north of Perth.

The GDC Observatory opened on Tuesday evening to coincide with the sky show.

Professor Blair had predicted the facility's Leaning Tower of Gingin would provide the perfect viewing platform for both the eastern and western horizon.

"We have three new telescopes, plus a big telescope coming from the United States Air Force Academy," he said.

"These telescopes make our centre the biggest public astronomy centre in Australia.

"It's all been revamped. It's going to be a great place for people to come and celebrate the skies."

400-metre asteroid passing by on Halloween

There will be another spectacle in the skies on Halloween this coming Saturday.

An asteroid is due to pass by Earth on October 31.

Known as asteroid 2015 TB145, it was only spotted by scientists on October 10.

It will be difficult to see with the naked eye but will pass closest to the Earth at 1:00am (AWST) on Sunday, November 1.

"It's going to miss the Earth luckily because it is 400 metres in diameter and shooting past at 30 kilometres per second on Halloween," Professor Blair said.

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