By Elissa Steedman, ABC
A long lens photo of a sturgeon super moon rising over Istanbul's Blue Mosque, in Turkey, in August 2023. Photo: AFP/ Yasin Akgul
Photography fans and stargazers are in for a show this week.
A "blue" supermoon will light up the sky across the world, with New Zealanders able to see it if our skies stay clear of clouds.
Let's break down what that means and what you can expect.
When is the best time to see the supermoon?
Technically, NASA says it will occur on Tuesday, 20 August at 4.26am AEST.
That's because an optical illusion occurs when the Moon is sitting low on the horizon that makes it appear larger.
And while Tuesday night is the peak time to catch the sturgeon supermoon, it will still look impressive on the nights and early mornings surrounding that day too.
What is a supermoon?
The moon doesn't actually grow bigger - it just looks that way.
According to NASA, the term refers to when the Moon, either its full or new lunar phase, syncs up with a close swing around Earth.
That is, when it is within 90 percent of its closest approach to Earth, to be exact.
But since we can't see new moons very easily, the term most often refers to when the Moon is full.
Because the Moon's orbit around Earth is not a perfect circle, there are times when it is closer to Earth.
That's when it looks biggest to us on Earth.
Why is it called a sturgeon supermoon?
All the full moons throughout the year have names, which can be traced back to a US reference book called the Old Farmer's Almanac, first published in 1792.
The book, which is published every September, contains things like weather pattern forecasts, moon phases and gardening tips.
The Old Farmer's Almanac is still in print. Photo: Supplied/ Harper Collins
Each full moons' name was given to it based on seasonal milestones.
Here's the name for each month's moon:
- January: Wolf Moon
- February: Snow Moon
- March: Worm Moon
- April: Pink Moon
- May: Flower Moon
- June: Strawberry Moon
- July: Buck Moon
- August: Sturgeon Moon
- September: Harvest Moon
- October: Hunter's Moon
- November: Beaver Moon
- December: Cold Moon
You might have noticed some of these names - like the snow moon and cold moon - don't quite fit in with our calendar year.
That's because the lunar names are based on Northern Hemisphere seasons.
Will it look blue?
No.
While that's what the name would suggest, the term 'blue moon' actually describes when we get multiple full moons in a given period.
There are two kinds of blue moons.
A seasonal blue moon refers to the third full moon in a season that has four.
A monthly blue moon is when we get a second full moon within the same calendar month.
This one earns its 'blue' status for being the third full moon in a season of four.
This supermoon was snapped rising over the Frederick Douglass Memorial Bridge in Washington, DC on 1 August, 2023. Photo: AFP/ Bryan Olin Dozier
How rare are blue moons?
You'd be forgiven for thinking blue moons are somewhat rare, thanks to the saying 'once in a blue moon'.
But according to NASA, a monthly blue moon occurs once every two-and-a-half years.
There can be rare occurrences around blue moons, though - it's not often we see two blue moons in the same year.
That only happens about four times a century, with the most recent being in 2018.
How rare are supermoons?
We usually get three or four supermoons a year.
And because they always happen one after another, we'll see about that many in a row in the coming months.
When is the next supermoon?
This will be the first supermoon of the year.
According to the BBC's Sky at Night, the next ones will occur on:
- 18 September
- 17 October
- 15 November (a new moon)
- ABC / RNZ