East Coasters are most likely to get a good view of New Zealand's best supermoon in almost 70 years - if the weather gods are kind.

The supermoon - which will appear as a big yellow ball - will creep over the eastern horizon at 8.45pm on Tuesday.

Astronomers are predicting it will be the most impressive supermoon since 1948.

It will be about 14 per cent bigger and 30 per cent brighter than an apogee full moon - and there won't be a closer full moon until 2024.


WeatherWatch head forecaster Philip Duncan said the east coast of both islands were likely to have the clearest skies on Tuesday evening.

"There's a fairly high chance of cloud in the north and west of both islands. It's not everywhere but at this stage it's looking fairly cloudy. The east areas shouldn't be too bad."

Christchurch residents would have a good chance of seeing the supermoon, as well as those in Hawke's Bay.

Wellingtonians and Aucklanders may catch a glimpse of it. "It's not an exact moment, so you've basically just got to stay up and hope for a break in the clouds."

MetService meteorologist Lisa Murray also expected East Coasters to catch the best views, particularly those in the South Island.

"There's rain moving in for much of the North Island and the West Coast which is expected to linger."

Auckland's Stardome Observatory astronomer Grant Christie said the best time to see the supermoon was as it rose after sunset.

"It's only when the moon's near the horizon that you get any appreciation of its size. Once it's high up in the sky, you don't really notice any particular difference."

The phenomenon occurs when a full moon coincides with its closest approach to Earth.

As its orbit around Earth is an ellipse, not a circle, the moon's distance from Earth can vary from a distant apogee of 406,000km to a closer perigee of 357,000km, although these ranges can also vary because the orbit of the moon is affected by the sun's gravity.

The moon passes through apogee and perigee each lunar cycle, and the phases of the moon and the orbit aren't directly linked, so occasionally a full moon will coincide with perigee, resulting in a supermoon.

The moon will actually be closest to the Earth - just 356,509km away - at 12.23am on Tuesday.

The exact time of the full moon occurs a little after this at 2.52am, at which time the moon will appear high in the sky and noticeably brighter.

The supermoon of 2014, as viewed from the International Space Station. Photo / File
The supermoon of 2014, as viewed from the International Space Station. Photo / File