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NOVA

With the US eclipse just over a week away, here’s how you can watch it safely.

Watch an Eclipse Safely

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<div class="rich-text">Here’s how you can watch a solar eclipse safely.
</div>

Here’s how you can watch a solar eclipse safely.

<div class="rich-text">Here’s how you can watch a solar eclipse safely.</div>

Space & Flight

<div class="rich-text">

 Onscreen
 
 : How do you watch an eclipse without frying your eyeballs?



 Chou
 
 : One patient I saw, he ended up with this whole constellation of retinal burns.



 Onscreen
 
 : Ralph Chou is a retired Professor of Optometry at the University of Waterloo.



 Chou
 
 : There's no pain receptors at the back of the eye, so you have no way of telling you've damaged the back of the eye.



 Onscreen
 
 : Dr. Chou is also an eclipse chaser.



 Chou
 
 : It's around 25 I've seen over my lifetime. It doesn't get old.



 Onscreen
 
 : Looking at the sun (even during an eclipse) can cause your eyes extreme damage.



 Chou
 
 : This patient I mentioned, he had his peripheral vision, he could walk around and do things, but he was legally blind in the sense that he couldn't read anything.



 Onscreen
 
 : Direct sunlight overloads the cells of the retina that allow detailed, color vision.



 Chou
 
 : The cells themselves start to break down. They release very nasty chemicals that will actually attack the innards of the cell.



 Onscreen
 
 : Leading to cell death, scarring, and blind spots in the extreme. The Sun can also scorch and kill the cells that send oxygen and nutrients to the retina. The amount of eye damage depends on how much of the Sun you see. So for someone who looks at just a crescent of the Sun…



 Chou
 
 : They're gonna end up not with a round burn on the back of the eye. They'll end up with a crescent shape.



 Onscreen
 
 : Any amount of direct sunlight is dangerous. So you need protection. Not sunglasses. Not glacier glasses. You need eclipse glasses that meet the ISO 12312-2 standard.



 Chou
 
 : Eclipse glasses contain a specially designed filter that will reduce the amount of light reaching the back of the eye by a couple of hundred thousand times. Just enough to be able to see the Sun through it.



 Onscreen
 
 : Don't take your eclipse glasses off if any part of the Sun is visible. It's only when the Sun is completely covered by the moon… only during these few short moments of totality… that it's safe to remove your eclipse glasses and look directly at what's left of the Sun—a glimmering halo of light.


 As soon as the tiniest bit of sunlight reappears, you must put your eclipse glasses back on.


 Warning! If you're using a telescope, binoculars, or even a camera, the Sun can burn a hole through your eclipse glasses. So the front of any optical device must be fitted with a special solar filter when pointed at the Sun.


 The eclipse should leave an indelible mark in your memory, not on your eyeballs.


 For safety recommendations, visit:
 <a href="https://eclipse2017.nasa.gov/safety">
 https://eclipse2017.nasa.gov/safety
 </a>
</div>

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