So, you want to watch the solar eclipse on Mon., Aug. 21. Good! You should! The U.S. is in the path of totality for the first time in most of our lifetimes, and it probably won't be again in our lifetimes — this isn't an event to miss. However, if you do choose to watch the solar eclipse, you might be wondering when you really need to wear solar eclipse glasses to watch the planetary event. I mean, surely if you look up at the eclipse during full totality, it'll be dark enough for your eyes to be protected?
Absolutely not. If there is one thing you absorb from reading this article, please, please make sure it is this: You must wear NASA-approved solar eclipse glasses (aka, not your regular sunglasses) the entire time you are looking up at the eclipse. No taking them off for just a second, no even glancing out your window without the glasses on to get a peek before you head outside. It's extremely dangerous for your eyesight, and could lead to temporary or even permanent blindness.
Why? The reason is pretty complex, but the gist is basically that when we look up at the sun in all its eclipseless glory, our eyes know to put up shields, so to speak, to protect the delicate inner workings of themselves — for instance, our pupils shrink rapidly so that less light enters the eye. We're still left with a bright spot in our field of vision after looking at anything bright, but because of these safeguards, it's just temporary. Damage occurring during an eclipse might not be, though. Because the sun is dimmed a substantial amount during an eclipse, our eyes can't adjust like they'd normally be able to while looking up at the sun. The pupils remain dilated, and what little sunlight that's visible behind the moon shines directly into our eyes. That can cause serious damage. So, the glasses act as a shield, allowing you to safely look up at the solar eclipse without hurting yourself.
The glasses, again, must be NASA-approved — you can't just wear any old sunglasses, even if they're designer. The standard for the lenses as released by NASA are ISO 12312-2. Additionally, if the glasses are at all scratched, do not wear them.
Now, none of this means you should be scared of the solar eclipse — again, it's going to be an amazing sight to see! Just ensure you take all of the proper precautions while viewing it, because it could seriously save you a lot of pain and trauma in the long run.