Today, millions of people will have a chance to watch a total solar eclipse. If you’re one of them, be careful: looking directly at a solar eclipse without eye protection can permanently damage your vision.
It doesn’t matter if our rocky satellite is blocking all or some of our nearest star—the sun is still an incredibly bright source of light. Don’t risk your eyesight for a quick glimpse or even a once-in-a-lifetime event. Thankfully, it’s pretty easy to protect your eyes while watching an eclipse.
What happens if you look at a solar eclipse
We are able to see thanks to photoreceptors. These cells, also known as rods and cones, are located at the backs of our eyes, and convert the light reflected by the world around us into electrical impulses that our brain interprets as the image we see. But when strong light, like that from the sun, hits our eyes, a series of chemical reactions occur that damage and often destroy these rods and cones. This is known as solar retinopathy, and can make our eyesight blurry. Sometimes, if the damage is too great in one area, you can lose sight completely.
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On a typical sunny day, you almost never have to worry about solar retinopathy. That’s because our eyes have natural mechanisms that ensure too much light doesn’t get in. When it’s really bright outside, our pupils get super tiny, reducing the amount of sunlight that can hit your photoreceptors. But when you stare directly at the sun, your pupils’ shrinking power isn’t enough to protect your peepers.
This is where your eyes’ second defense mechanism comes into play. When we look at something bright, we tend to blink. This is known as the corneal or blink reflex, and it prevents us from staring at anything too damagingly bright.
Just before a solar eclipse has reached its totality, the moon is partially blocking the sun, making it a lot easier for us to look up at the star without blinking. But that doesn’t mean you should—even that tiny sliver of sunlight is too intense for our sensitive photoreceptors.
[Related: Total eclipses aren’t that rare—and you’ve probably missed a bunch of them]
Unfortunately, if you practice unprotected sun-gazing, you probably won’t know the effects of your actions until the next morning, when the damage to your photoreceptors has kicked in.
And while solar retinopathy is extremely rare, it is by no means unheard of. If you search the term in medical journals, you’ll find case reports after almost every popular solar eclipse. Let’s try really hard to do better this time, eyeball-havers.
How to safely watch a solar eclipse
Watching the eclipse with your own two eyes is easy: just wear legitimate eclipse sunglasses. These are crucial, as they will block the sun’s rays enough for you to safely see the eclipse without burning your eyes out.
And if you don’t have eclipse glasses, you can still enjoy the view, albeit not directly. Try whipping up your own eclipse projector or a DIY pinhole camera so you can enjoy the view without having to book an emergency visit to the eye doctor.
This story has been updated. It was originally published in 2017.
