The sun will dim tomorrow morning during a rare solar eclipse.
Wanganui astronomer Ron Fisher said a solar eclipse was caused by the moon moving across the sun.
In parts of Australia the eclipse will be total - turning day into night - but in Wanganui around 80 per cent of the sun will be blocked out, Mr Fisher said.
"Generally, the further north you go, the more of the eclipse you'll see."
Up to 91 per cent of the sun would be blocked out on Northland's east coast, but less than 60 per cent would be obscured in the far south of the South Island.
The last partial eclipse observed in Wanganui was in 2008, and the next significant eclipse will not be seen here until 2025.
Mr Fisher said tomorrow's eclipse would begin around 9.25am and finish around 11.45am, with the peak time being around 10.32am.
He said in Wanganui the eclipse was unlikely to be noticeable to people going about their ordinary business. On a fine day, the sun would dim to the same level as a cloudy day.
However, for those who are interested in the eclipse, the event offers the opportunity to view what Mr Fisher calls "one of the wonders of the universe".
"During a solar eclipse the sun, moon and earth are all perfectly aligned. If you get a chance to see it, it is a remarkable sight."
However, he warned people they need to have proper viewing equipment to see the phenomenon. He suggested people head to the Ward Observatory or wear a pair of special solar glasses to view the eclipse.
Two Wanganui optometrists, Wanganui Eyecare and Eyes On Victoria, have limited numbers of solar viewing glasses they will give away to the public on Wednesday morning.
Kerry Bennett from Eyes On Victoria said wearing sunglasses would not protect your eyes if you looked directly at the sun - even during an eclipse.
"If you look directly at the sun without proper protection you can literally burn a hole in the back of your eye and permanently damage your eyesight," he said.
Mark Lee from the Wanganui Astronomical Society said the Observatory, located in St Hill St, would be open from 8.30am.
"We'll be open all morning, and the public is welcome to come and view the eclipse."
At least four telescopes would be set up for viewing, and special solar viewing cards sold for $3 each.
MetService is forecasting cloudy periods for Wanganui tomorrow.
Meanwhile, thousands of scientists, astronomers and umbraphiles [eclipse watchers] are expected to descend on the northern Queensland city of Cairns, which will experience the full eclipse.
Studies will be made of the psychological effect of the eclipse on humans, and the marine life of the Great Barrier Reef and Queensland's rainforest birds and animals will be studied to observe the eclipse's effect on them.