Extract from ABC News
August is going to be a big month for Moon watchers, with two supermoons happening in the same month.
The month will kick off with what's known as the "sturgeon supermoon".
And it'll end with a "blue supermoon" (although it won't be coloured blue).
When is the next full moon?
In Australia, it'll be Wednesday, August 2 — that's the sturgeon moon.
Then we'll get to see another full moon on Thursday, August 31 — that's the blue moon.
They'll both be supermoons.
What is a supermoon?
It's when there's a full moon at the same time the Moon is closest to Earth.
The Moon's orbit around Earth isn't a perfect circle.
So there are times in the Moon's orbit when it's closer to Earth — that's called the perigee.
When this happens, the Moon is 363,396km from Earth.
So because it's closer to us on Earth, the Moon looks bigger — even though the Moon itself doesn't change in size.
The opposite of this is the apogee, when the Moon is 405,504km from Earth
A supermoon happens when a full moon occurs at the same time as a perigee.
And when a full moon coincides with the apogee, it's called a micromoon.
"Supermoon" isn't really a technical term, but it's generally applied when the Moon is 90 per cent or closer to its perigee.
A supermoon appears 14 per cent bigger than a micromoon and 30 per cent brighter.
But NASA's Jet Propulsion Laboratory Education Office says it's not that noticeable.
"A 14 per cent increase in the apparent size of something that can be covered with a fingernail on an outstretched arm won't seem significantly bigger," NASA says.
So don't be disappointed when the Moon doesn't take up the whole night's sky.
"A technique that involves using a long telephoto lens to take photographs of the Moon next to buildings or other objects makes the Moon look huge compared with its surroundings," NASA says.
"There are also images that have been edited to inaccurately dramatise the size of the supermoon.
"Both of these can lead students, and adults, taking pictures with their cell phone to think that they've done something wrong or just aren't cut out for observing the sky, which isn't true."
What is a blue moon?
A blue moon is when a full moon happens twice in a calendar month.
It's fairly rare. NASA says blue moons usually only happen every two and a half years.
It's even rarer for a blue moon to be a supermoon because we usually only get three or four supermoons a year.
Why is it called a 'sturgeon supermoon?'
Again, this isn't a technical, scientific term. It's more of a nickname.
And it's a northern hemisphere thing.
The name sturgeon moon comes from a US publication called The Old Farmer's Almanac, which is an annual magazine that's been in print since 1972.
"The full moon names used by The Old Farmer's Almanac come from a number of places, including Native American, colonial American, and European sources," the publication's website says.
"Traditionally, each full moon name was applied to the entire lunar month in which it occurred, not solely to the full moon.
"August's full moon was traditionally called the sturgeon moon because the giant sturgeon of the Great Lakes and Lake Champlain were most readily caught during this part of summer."
Here's a bunch of alternative names for the August moon, listed by The Old Farmer's Almanac:
- Black cherries moon
- Corn moon
- Flying up moon
- Harvest moon
- Mountain shadows moon
- Ricing moon
When is the next supermoon?
After August, Australia's next supermoon will be on Friday, September 29.
That'll be the last supermoon of the year.
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