Do Supermoons Matter? Yes! Why You Need To See Tonight’s ‘Equinox Supermoon’ And Its ‘Moon Illusion’


The full moon rises behind trees in Lisbon Sunday, Jan. 20 2019.ASSOCIATED PRESS

Later today at dusk across the world, the year’s third, final and best supermoon will rise close to the moment of the vernal (or spring) equinox. It will be slightly bigger than most full moons because of its proximity to Earth, but you are not going to notice that. So what’s the point of all the hyperbole around a supermoon?

Here are the reasons why the supermoon will look bigger than most full moons, and why supermoons matter.

clear full moon behind mountains golden hourGetty

What is the ‘supermoon illusion’?

It’s to do with the human brain’s perception of size and scale. If you don’t look at the moon all that much, watch the “Super Worm Equinox Moon” (March’s full moon is sometimes known as a “Worm Moon” because of the seasonal appearance of earthworms in North America) appear on the eastern horizon (it will actually appear perfectly due east on March 20) and it will seem enormous and dramatic. “The ‘moon illusion’ makes watching a moonrise a wonderful experience because the moon seems to be bigger than it actually appears in the sky,” says Tom Kerrs, an astronomer at the Royal Observatory Greenwich in London, and author of Moongazing: Beginner’s guide to exploring the Moon. “The human brain understands the geometry of the sky, but it doesn’t see the sky as a dome, so it doesn’t project things correctly near the horizon,” he explains. “So everything at the horizon gets oversized in your mind’s eye compared with the foreground.”

Full moon behind San Luca basilica church on the Bologna hills of Italy.Getty

How to destroy the ’supermoon illusion’

It’s very easy to destroy this strange and beautiful effect. “You can shatter the illusion by just holding out your little finger at arm’s length and covering the moon,” says Kerrs. “But as soon as you take your finger away again, your brain will think the moon is bigger.”

Since the “moon illusion” will be slightly heightened for the rise of the Super Worm Equinox Moon, dusk is the time to get high and look east.

The full moon rises behind the Graca Monastery in Lisbon, Tuesday, Feb. 19 2019, the year’s second supermoon. (AP Photo/Armando Franca)ASSOCIATED PRESS

Do supermoons matter?

We hear a lot about them in the mass media, but astronomers often play down their significance and are puzzled as to why they’re so popular. However, they are certainly significant. “The culture and the physics don’t marry perfectly, but all cultures have a strong tradition of anything big and bright in the sky, whether it’s a moon, a meteorite, or a comet,” says Tristan Gooley, author of The Nature Instinct and editor of The Natural Navigator. “It gets slightly inflated in terms of its impact on us, but the actual physical nature of a supermoon is real.”

For example, supermoons have a very special significance to anyone who lives near the coast. “Since it’s a full moon and it’s particularly close to us there are certain very definite relationships, and the biggest one is tides,” says Gooley. “It has a bigger impact on the force of the tides than a lot of people might imagine,” he says. “If you’re within 20 miles of the coast you’ll notice an impact on the behavior of birds and all animals.”

How does a supermoon affect the tides?

“The proximity of the moon to Earth has a bearing on the height of tides,” says Gooley. “You get a big spring tide where the high and low tide are more extreme than normal.” A neap tide is when the sun and moon are influencing the oceans separately, so the range between low and high tide is smaller, while a spring or ‘king’ tide is when the sun and moon work in concert, so they have a combined gravitational impact, and the ranges are therefore bigger. “A supermoon is an extreme version of a full moon, so it’s ramped up even more and you get abnormally big ranges,” says Gooley. Technically, it’s called a perigean spring tide.

A supermoon at full moon causes a perigean spring tideGetty

After the Super Worm Equinox Moon has passed, the next really big supermoon will be the “Super Pink Moon” of April 8, 2020.

Wishing you clear skies and wide eyes

Follow me on Twitter @jamieacarter@TheNextEclipse or read my other Forbes articles via my profile page.

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