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Particle 101: Solar Eclipses

Parts of Western Australia will be plunged into darkness during a once-in-a-lifetime solar eclipse on 20 April.
Thomas Crow
Thomas Crow
Freelance science writer
Particle 101: Solar Eclipses
Image credit: NASA Photo / Carla Thomas

An eclipse is an incredible natural phenomenon to witness (safely!).

It also offers scientists a chance to study the structure and activity of the Sun’s corona – a jacket of super-hot gases that surround the fiery planet.

The magnetic fields that influence the behaviour of these gases can cause solar flares and solar winds.

These events can mess up communications equipment and satellites, so it’s valuable to measure the corona to predict when they may occur.

WHAT IS A SOLAR ECLIPSE?

A solar eclipse occurs due to rotations and orbits between the Sun, the Earth and the Moon.

The Earth rotates on a tilted axis of 23.5 degrees. This means some parts of the Earth are closer to the Sun than others.

This difference is why we have time zones, inverted seasons in the northern and southern hemispheres and the illusion of the Sun moving across the sky.

While we spin and orbit around the Sun, the Moon orbits around Earth. A solar eclipse happens when the Moon passes between the Sun and the Earth, blocking the Sun’s light from reaching our planet.

How the Sun, Moon and Earth align for an eclipse | NASA’s Goddard Space Flight Center

The Earth experiences around four to seven solar eclipses each year. Depending on where you live, you might not experience them all.

The eclipse on 20 April is best viewed from Australia, particularly Ningaloo, near Exmouth, Indonesia and South Asia.

TYPES OF SOLAR ECLIPSES

You may be wondering how the Moon can block the Sun when it’s 400 times smaller and roughly 400 times further away.

Well, it’s actually an illusion caused by forced perspective. You can create the same illusion by catching the Sun between your fingers.

Arie Zimet/Wikicommons

The 20 April eclipse is a hybrid eclipse. This is a combination of an annular, partial and total eclipse.

An annular solar eclipse occurs when the Moon obscures the Sun during the point in the Moon’s monthly cycle where it’s furthest from the Earth.

A partial eclipse involves the Moon partially covering the Sun from our perspective.

This is what we’ll see from Perth this week between 8am and 12.46pm. The eclipse will reach its peak at 11.20am when the Moon will cover 70% of the Sun. A partial eclipse can last for hours.

In contrast, a total eclipse might last anywhere between 10 seconds and 7.5 minutes. (The next one to last that long won’t happen until 2186.)

THE DARK SIDE OF THE MOON

The umbra is the area of shadow where the Moon completely blocks the Sun for the people below.

The broader shadow – where people can look up to see the Moon partially blocking the Sun – is called the penumbra.

Ningaloo, near Exmouth, is the best place to view the 20 April eclipse because it will be beneath the umbra. This makes it one of the only places on Earth to experience a total solar eclipse from 11:28am.

The closer you are to Exmouth, the more ‘total’ the eclipse will appear. However, it’ll only last 58 seconds, so make sure you’re really living in the moment if you want to experience the eclipse.

GIPHY

HOW TO SAFELY VIEW AN ECLIPSE

It’s not safe to look directly at an eclipse without specialised eye protection.

While the Moon might cover most of the Sun, there will still be enough visible light to damage your eyesight.

Do NOT do this | GIPHY

Experts warn against using cameras, binoculars or telescopes to view the eclipse without purpose-built filters. Without the proper filter, these viewing tools will focus the incoming sunlight directly into your eyes and quickly cause damage.

Also, do not use the old eclipse glasses or filters that have been hanging around your house since the last eclipse. There’s no guarantee that they’re still safe.

What if the weather is crap?

If the weather isn’t favourable where you are, Scitech is live-streaming the eclipse from Exmouth.

Thomas Crow
About the author
Thomas Crow
Thomas Crow is an Australian science writer. He has a background in professional writing, biochemistry and genetics. He writes for Australian and New Zealand research institutes and publications like Crikey. He's a horror and gothic fantasy fan. He thinks of himself as a gardener but scores of dead plants beg to differ.
View articles
Thomas Crow is an Australian science writer. He has a background in professional writing, biochemistry and genetics. He writes for Australian and New Zealand research institutes and publications like Crikey. He's a horror and gothic fantasy fan. He thinks of himself as a gardener but scores of dead plants beg to differ.
View articles

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