Why is tonight’s full moon called a pink supermoon?


If the clouds are accommodating, then tonight’s full “pink moon” will be a little bit bigger in the sky, as our planet’s only satellite is almost as close to us as its orbit allows.

But there are a few misconceptions, says Australian astrophysicist Prof Jonti Horner, about the names some people give to full moons.

Right about now in parts of North America, a native herb known as creeping phlox is coming into its pink bloom.
Horner says in the United States, there’s a tendency towards using the names that Native Americans have for full moons.

“Last month it was a wolf moon,” says Horner, of the University of Southern Queensland.

The pink moon is named not because it will take on a particular colour, but because of the colour of the flowering phlox.

Modern skywatchers term tonight’s phenomenon a “supermoon” – a term coined by an American astrologer Richard Nolle in 1979.

Technically, we get a supermoon when a full moon occurs around the time our satellite reaches perigee – its closest point to the Earth.

Horner says tonight’s moon “definitely won’t be pink” but if you’re somewhere where there is pollution in the air, then it could take on a more reddish tinge.

Horner says a supermoon is only about 15% bigger and brighter than a usual full moon – not really enough to be noticeable to most humans.

The moon always seems larger when it is closest to the horizon, but Horner says this is down to a phenomenon known as the “moon illusion”, rather than the satellite actually being any closer.

“When it’s low to the horizon the moon looks bigger than it does when it’s overhead, but that’s more because we have a point of reference. It’s all about perception,” he says.

To counteract this illusion, Horner says that if you can do it safely (and you’re flexible enough), you should bend over and view the moon through your legs, although it’s not agreed why this trick through the legs actually reduces the effect of the moon illusion.

fields of pink flowers
The United States has a tendency to use names that Native Americans have for full moons, with this one named for the pink flowering phlox. Photograph: VCG/VCG via Getty Images
The reason the moon can sometimes appear to glow orange as we view it closer to the horizon, is because the light has to travel through more of the Earth’s atmosphere than it does when the moon is overhead.

The atmosphere scatters the light, filtering blues and then yellows and leaving visible oranges and reds.

In Sydney, the air quality is currently low because of particles from hazard reduction burning in bushland on the city’s outskirts. Sydneysiders have been viewing a reddish moon through this haze in recent nights.

“If you have more pollution, then the more enhanced the effect,” says Horner. “It’s the same reason why if you have bushfires the sun can go blood red. It’s the same reason why the sky is blue.”
When the Earth is lined up between the sun and the moon, we get a full moon. But next month’s full moon – which will also be a supermoon – will see the satellite pass through the Earth’s shadow for a total lunar eclipse visible in east Asia and Australia as well as across the pacific and Americas.

“That’s much more interesting than a super-whatever-moon,” says Monash University astrophysicist Prof Michael Brown

“During a total lunar eclipse, when the moon is in the Earth’s shadow, the only light reaching the moon passes through the Earth’s atmosphere. That produces a red tinge, or a deeper red colour after big dirty volcanic eruptions.”

About the author

Olivia Wilson
By Olivia Wilson


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