‘Shadow snakes’: What it’s like in the dark heart of a solar eclipse

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Astronomers will criticise me if I don’t kick things off with a warning: Do not look at the sun or an eclipse unless you have viewing glasses that meet the ISO 12312-2:2015 safety standard. That includes former US presidents.

Donald Trump glances at the sun during a 2017 solar eclipse, an act that can cause permanent eye damage. Right: Eclipse chaser David Finlay views a solar eclipse correctly through protective goggles.Credit: Andrew Harnick, David Finlay

Now that’s done, I can tell you that thousands of “eclipse chasers” have descended on the West Australian town of Exmouth, 1250 kilometres north of Perth, where the moon will completely block out the sun during Thursday’s rare hybrid solar eclipse.

Most of Australia will experience a partial eclipse. In Sydney and Melbourne, the shadow of the moon will block about 20 per cent of the sun, starting at 1.36pm in Sydney (AEST) and 1.15pm in Melbourne.

I rang photographer David Finlay, who has travelled more than 5000 kilometres in his 2006 Prado from Kiama, south of Sydney, to Exmouth to park himself right in the “path of totality”.

For Finlay, even the parts of WA where the sun will be 99 per cent obscured are not enough.

“That’s kind of like going to a Madonna concert and standing at the ticketing booth,” he says. “The main show is the totality.”

The hybrid eclipse

A solar eclipse occurs when the sun, moon and Earth form a “syzygy”, the moment when three celestial bodies line up perfectly (and a word that makes for a deadly weapon in any Scrabble battle).

It’s made possible by an excellent cosmic coincidence – the sun is 400 times larger than the moon, but the moon is 400 times closer to Earth. That makes it possible for the moon’s shadow to fully obscure the sun.

A total eclipse occurs for people viewing the sun (through goggles!) from the centre of the moon’s full shadow, or umbra.Credit: CSIRO

Thursday’s “hybrid eclipse” occurs in only 3 per cent of solar eclipses.

It will begin as an annular eclipse over the Indian Ocean. The moon’s umbra, or full shadow, won’t quite reach Earth, so the eclipse will appear as a dark, round moon fringed by a halo of sunlight, or “ring of fire”.

By the time the eclipse’s path of totality passes over Exmouth, the umbra will make it to Earth and cause a total solar eclipse.

Right before totality, a “diamond ring” effect occurs as the last of the unobscured sun bursts through valleys on the moon.Credit: AP

What’s it like to stand in ‘the shadow’?

“You start to get this chill,” says Finlay, who has viewed five total solar eclipses. “The light goes really strange. You’ll spread your fingers out to cast a shadow and they’re curved, like talons. It’s so weird.”

Then come the slithering “shadow snakes” – an unexplained phenomenon where bands of shadow flash across the ground.

“There are like these ripples of snakes racing across the ground in front of you. You’ll never see anything like that other than in a solar eclipse,” Finlay says. “That heralds the totality.”

Researchers plan to observe space weather using CSIRO’s ASKAP radio telescope by measuring the twinkle of distant galaxies during the eclipse. Credit: CSIRO

Only then can viewers whip off their eclipse goggles – in Exmouth, for about 60 seconds until a sliver of sun reappears – and admire the sun’s magnificent corona, bursting out around the moon’s silhouette in arcing white streams.

“It’s this incredible connection of humanity to space … It’s like the universe is opening itself up to us and giving us love,” Finlay says. “I challenge anyone to feel hatred or a negative emotion during a solar eclipse.”

Even the CSIRO’s deputy director of space and astronomy, Dr Mark Cheung, speaks in poetry to describe the totality.

“It’s a life-changing experience,” he says. “You feel the sky getting dark all around you as if the day is punctuated by night. The stars come out. Your surroundings take on a different character, as if another palette was used to paint the land and the sea.”

A map showing the trajectory of five total solar eclipses which will be visible in Australia between 2023 and 2038.Credit: Eclipse Chasers

What can eclipses teach us?

Scientists will leap on the opportunity to study the sun’s surrounding atmosphere, or corona, on Thursday. The corona is a million times dimmer than the sun, which makes it difficult to observe.

“The sun’s corona consists of gases where electrons are stripped from the atoms and you have this ionised plasma that is millions of degrees hot,” Cheung says.

“We are still trying to understand why the sun’s corona is so hot, and how this hot corona blows the solar wind that permeates the solar system.”

A CSIRO radio telescope will take advantage of the temporary decrease in radio waves from the sun to aim at twinkling distant galaxies. This will allow astronomers to better calibrate their observations and understand how solar wind interferes with the light coming from other bodies in space.

The Sydney totality

Four more solar eclipses are set to pass over Australia in the next 15 years, including in 2028, when the path of totality will cut right through Sydney. A total solar eclipse occurs in each location on Earth about once every 375 years.

“There will be a very much more substantial Australian population who will be at or near the path of totality and will be able to experience this astronomical spectacle,” Cheung says.

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