Stargazers are about to be treated to a blue supermoon: a rare lunar spectacle that won’t be seen again in New Zealand’s night skies for nearly a decade. 

The rare display, appearing on Thursday, will be the biggest and brightest moon of any this year – and also the second super full moon to appear in a single calendar month. 

While a blue moon occurred once every two to three years, one that coincided with a supermoon was rarer. 

The last blue supermoon was in 2009, and the next wasn’t due until 2032. 

A supermoon looms over Auckland on August 12 last year. Photo / Brett Phibbs 

A supermoon was when a full moon happened near the lunar body’s closest point to Earth in its orbit, making it appear brighter and larger than average. 

“Supermoons look about 8 per cent bigger and about 16 per cent brighter than an average full moon,” Stardome astronomer Rob Davison said. 

“A blue supermoon is a lovely quirk of our calendar, which means we’re seeing two of these bigger and brighter moons in the same month.” 

The moon’s orbit was slightly elongated, meaning its distance from Earth ranged between about 364,000km and 404,000km, although variances could bring it a little closer or farther away. 

Typically, only two to three full moons qualified as a supermoon each year – and this month’s first happened overnight on August 1. 

But the end-of-August supermoon would be the biggest and brightest of the year, because the moon would be more than 27,000km closer to Earth than its average distance of 384,000km. 

“The super blue moon will rise towards the east as the sun sets towards the west, and will be visible in the sky for the whole night,” Davison said. 

“If it’s a clear night, people will be able to see it from all over the country.” 

MetService meteorologist Ngaire Wotherspoon said Thursday night’s prospects for moon-viewing looked more positive than tomorrow’s. 

“While there’ll be some cloud around and a few showers north of Auckland, Auckland itself shouldn’t be too bad and will have some fairly clear skies,” she said. 

MetService was also forecasting plenty of clouds for central parts of the North Island, with skies likely to be clearer on the coasts. 

“And the South Island is pretty similar, with a lot of cloud along the West Coast and around Nelson that night – but hopefully, it should be lovely in eastern regions.”