Photography fans and stargazers are in for a show this week.
A "blue" supermoon will light up the sky.
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, August 20 at 4.26am AEST.
But luckily for those who aren't early risers, the moon will appear at its biggest around dusk this evening.
That's because an optical illusion occurs when the Moon is sitting low on the horizon that makes it appear larger.
And while Monday night is the best time to catch the sturgeon supermoon, it'll still look impressive on Tuesday evening, 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's within 90 per cent 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 isn't a perfect circle, there are times when it's 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.
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.
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:
- September 18
- October 17
- November 15 (a new moon)
