Home Science Solar Eclipse – What happens in the eye!

Solar Eclipse – What happens in the eye!

On August 21st 2017, people worldwide turned their attention to the skies to watch the moon move infront of the sun in a total solar eclipse in a once-in-a-lifetime event! The next day , google searches related to aching heads reached a record high. James Ashford explains why.

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For some on August 21st night came early! It then promptly left again; with confused flocks of birds and awed onlookers in its wake.

A total solar eclipse, visible last year over the central states of the USA, is one of the most staggering public astronomical sights and comes about from a wonderful quirk of local orbital geometry. Our sun, compromising about 99.86% of the mass in the solar system, has a radius around 400x larger than our moon but is simultaneously 400x further away. This chance similarity means that, at easily predictable times and locations, it is possible for our humble moon to entirely eclipse the visible disk of the sun. Not only does this lead to an impressive window for scientific investigation, such as Gravitational Lensing, but also a moment for us to look up at the skies in wonder at just how incredible space is.

 

What goes on in the Eye?

Whilst the eclipse is truly impressive, and a David/Goliath story to rival any other, an event that involves prolonged periods of looking at sun is likely to pose a serious risk to your eyesight if done without proper protection.

Before 1962 it was believed that the damage caused by the sun is due to tissue heating; the lens in your eye focuses incoming intense light and causes cell death by overheating. However, the research of physicist Johannes J Vos revealed that exposure to direct sunlight can only produce heating of up to 2oC, which is not enough to damage the retinal cells. This was confirmed in further research carried out by Werner K. Noell where specific wavelengths of light, at peaks around 500nm, would still damage the eyesight of rats even though the energy of those waves was insufficient to produce any dangerous cell heating.

Finally, the work of Malgorzata Rozanowska suggested an alternative photochemical mechanism for cell death involving an over production of the signal chemical all-trans-retinal. This can set off a dangerous cascade of free-radical interactions that leads to unchecked lipid oxidisation and finally cell death (see image).

So?

To completely avoid damage to your eye, the guidelines laid out by NASA state that your chosen filter must block out all but 0.003% of visible light and at all but 0.5% of the near IR light from the sun. In good news, this is all pretty easy to do – there are many brands of commercially available eclipse glasses for your eyes and Barder filters for your telescopes. If you’re hoping to see one from your back garden don’t hold your breath; we’ll have to wait until 2090 to experience the next totality in the UK. Although, if you’re up for a bit of eclipse-chasing you can get a flight to Chile or Argentina for 2nd July 2019; totally worth it!

Whilst the eclipse is truly impressive, and a David/Goliath story to rival any other, an event that involves prolonged periods of looking at sun is likely to pose a serious risk to your eyesight if done without proper protection.

Article by contributing writer James Ashford

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