This month's full moon coincides with its lunar perigee, the closest approach the moon makes to Earth, making the moon appear larger in the sky.
Grant Christie of Auckland's Stardome Observatory said the moon should appear about a 10th larger than normal.
"The moon's orbit is elliptical, so at various times it reaches its closest point to Earth and therefore it appears a little bigger in the sky and a little brighter.
Dr Christie said the so-called "supermoon" would have only a slight effect on tides.
The last supermoon was in March last year.
The moon will be at its fullest at 3.35pm NZT on Sunday.
"It does reach its closest moment in a particular point in time, but in terms of the visual impact ... you wouldn't notice a difference half a day either side, frankly," Dr Christie said.
According to Space.com meteorologist Joe Rao, this month's perigee will also be the nearest the moon will get to Earth this year, as the distance of the moon's closest approach varies by about 3 per cent.
The moon will be 356,955km from Earth.
Later this year the opposite will happen, with the November 28 full moon coinciding with the moon's apogee, its furthest approach, Space.com said.
- Paul Harper of Herald Online
