Australians were treated to the breathtaking spectacle on Tuesday night, with the moon appearing 17 per cent bigger and 30 per cent brighter than usual.

Onlookers watched the moon climb over Sydney Harbour, lighting up the sky behind the famous Opera House.

Although stunning, the moon was not actually pink. Its name relates to the timing of the supermoon.

"Hundreds of years ago the Americans used to call it the pink supermoon because a beautiful wildflower would bloom around the same time, so they would associate that with big, bright full moon," Astronomer Sara Webb told AAP.

The phenomenon, which usually takes place every year around April, is caused when a full moon occurs while it is on its closest approach to earth.

"It's one of those moons that when you're driving along or you're outside that you really like 'woah'."

This year Australians will be treated to two supermoons, with a blood supermoon due on May 26.

"We have one full moon as it is entering its closest point and one full moon as it is exiting its closest point ... so it is just a lucky coincidence," she said.

"This one is not false advertising in the name. It actually is bright red and it's because it's going to happen during a partial lunar eclipse."

Australian Associated Press