Easily one of nature’s most beautiful events, total solar eclipses are a rare sight for many. When a solar eclipse occurs, what you’re witnessing is the Earth, Moon and Sun aligning. Eclipses can only really happen at a new Moon. With this in mind, it’s quite easy to think that we should get an eclipse every month but because the Moon’s orbit around the Earth is tilted by around five degrees to that of our planet’s, our natural satellite’s shadow usually misses the Earth’s surface since it passes above or below the planet at this stage in its lunar phases. It’s only really at least twice a year that the geometry lines up just right to make an eclipse for some lucky observers in a particular part of the world.
The Moon’s shadow consists of two parts – the penumbra and umbra. It’s the fainter, outer penumbral shadow that hits the Earth and enables us to see a partial eclipse at first. It’s not until the Moon’s dark inner shadow – called the umbra – strikes the planet that we’re able to see a total eclipse. The track of the umbral shadow across the Earth is called the Path of Totality. At just 16,000 kilometres (10,000 miles) long and 160 kilometres (100 miles) wide, this is why there are few places in the world where you can see a total eclipse, since this path covers less than one per cent of the planet’s surface.
When the Moon passes in front of the Sun, we don’t always get a total eclipse. Instead, we get an annular eclipse, also known as a ‘ring of fire’ – that’s when the Moon is at a further distance from the Earth in its orbit and therefore appears smaller, unable to cover the Sun’s disc entirely. With the Moon at a distance of around 357,000 kilometres (222,000 miles) from us on 20 March, it will appear large enough in the sky to cover the entirety of the Sun from the more ideal eclipse-watching locations.
Experiencing a solar eclipse is like witnessing no other event. At first, a tiny dent will appear on the eastern side of the Sun’s face (western for a southern hemisphere solar eclipse). Initially you won’t be able to see it, but that small chunk out of the side of the Sun will become a gigantic bite out of the solar surface. This is point the excitement truly begins.
The Moon will leisurely move across the Sun’s face for the next half an hour or so. You’ll notice that the sky is still quite bright, but then it will start to take on a much deeper blue. The ground around your feet and around you appears dimmer as the ambient light fades to a grey.
When there’s about quarter of an hour left until totality, a portion of the sky will be much darker than the opposite side, no matter where the Sun is. Our star will become an ever-narrowing crescent but will still be incredibly bright, the sky changing to an extremely deep blue, almost purple. It will become darker as the the Sun’s light gradually becomes extinguished by the Moon creeping across it.
The sky will start to darken noticeably and continue to gather strength before spreading out along the horizon. It won’t be long until the minutes to totality turn into the long-awaited seconds and what’s left of the Sun is nothing but a bare sliver with Bailey’s beads popping into view: these are the final points of bright white light, where sunlight passes through the deepest lunar valleys. A thicker, blacker limb of the Moon continues to move across the Sun’s surface until our bright star is blotted out, apart from a white halo. This is what’s known as the corona, the Sun’s hottest and most extended atmosphere and it shines with a stunning pearly white glow.
At this point we’ve reached totality and you will now be standing in the shadow of our Moon. A great black disc will replace our Sun. The sky will be so dark that the stars and planets near to the Sun and above our horizon will be visible, almost like night truly has enveloped us.