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Why you absolutely cannot stare at the sun without eclipse glasses, explained

Stocks of eclipse glasses are running low. That’s not an excuse to forgo eye protection.

Becker & Bredel/ullstein bild via Getty Images
Brian Resnick is Vox’s science and health editor, and is the co-creator of Unexplainable, Vox's podcast about unanswered questions in science. Previously, Brian was a reporter at Vox and at National Journal.

If you’re going to stare at the sun during the upcoming solar eclipse on August 21, you need eye protection. Unfortunately, obtaining eye protection in recent days has become a major pain. Namely:

Still, there’s no excuse for not protecting your eyes if you’re going to admire the partial phases of the eclipse, when the sun is not totally covered by the moon. None at all. You either have to find some eclipse glasses, breaking out some very dark welder’s glasses, or use an indirect method — like a pinhole projector (more on that below) — to view the eclipse. Because if you don’t, you risk permanent eye damage.

So here’s a short guide to why staring at the sun is so bad for you, and what you need to look out for when purchasing or using eclipse glasses.

How the sun can burn a hole in your eyeball

The sun is the most powerful source of energy in the solar system. It’s the most energetic object for light-years in all directions (it’s literally a huge fusion reactor). The energy it expels is so intense it can actually burn holes in your vision.

And it’s particularly dangerous because of the anatomy of our eyes, Joel Schuman, chair of ophthalmology at NYU Langone Health, explains. When light enters our eyes, the lens focuses light to the retina, located in the back of the eye. We see thanks to the retina’s chemical sensors picking up on the presence of light and transmitting information to the brain.

The retina can handle indirect sunlight just fine. But think of what happens when you hold a magnifying glass up to the sun. It focuses light intensely enough to start a fire.

Something similar happens with the lens in your eye when it’s focused directly on the sun.

“The light from the sun is very intense and concentrated into a very small area, and then that light is converted into heat and that heat cooks the retina,” Schuman says. “So you have a permanent area that you don’t see, a permanent blind spot.” What’s worse, a retina burn doesn’t heal like a sunburn on the skin. It actually doesn’t heal at all.

Wikimedia Commons

It doesn’t heal because the retina is nerve tissue, Schuman explains, which doesn’t readily regenerate. Think of it like a spinal cord tear: permanent. And because the light from the sun hits the center of the retina, this burn occludes the sharpest region of central vision. “Oh, 20 seconds probably, that’s all it took,” Louis Tomososki, an Oregon man who was partially blinded during a total solar eclipse in 1963, told a local NBC affiliate. “Looking at someone and being able see their face — but not their nose” is how he described it to NBC.

In less severe cases, Schuman says, there may just be swelling in the retina. This can be treated with steroids or other anti-inflammatory drugs.

So be sure, if you think your eyes have been damaged, to see a doctor for treatment!

Normally we don’t look at the sun because it’s uncomfortable. But an eclipse is an opportunity to appreciate our place in the universe.

In 1999, a solar eclipse passed over the United Kingdom. Just one hospital alone in Leicester had 45 patients complaining of eye trouble, the journal Lancet reported. Twenty of the cases involved burns or inflammation to the retina.

So how do eclipse glasses work?

On August 21, a total or partial solar eclipse will be visible from every single US state. But wherever you are, “it is never safe to look directly at the sun's rays — even if the sun is partly obscured,” NASA warns. Even when the sun is 99 percent obscured, it can still cause damage.

That’s why during a partial eclipse — and even through the early and later phases of a total eclipse, when you can see the last bits of sun peeking through the craters of the moon — you’ll need eye protection. You can only take off the protective glasses when the moon has completely covered the sun during totality.

Regular sunglasses won’t block enough light. You’ll need glasses that filter all but 0.003 percent of visible light and block out most ultraviolet and infrared as well. “Such filters usually have a thin layer of aluminum, chromium or silver deposited on their surfaces that attenuates ultraviolet, visible, and infrared energy,” NASA’s eye safety page explains. Using photo or X-ray film is not safe.

(The same thing goes for looking through binoculars, mirrored cameras, or telescopes: If you’re looking at the sun through them, you’ll need to put special filters on the lenses.)

For your eyes, you could grab a pair of one of the darkest available (shade 12 or higher) welder’s glasses. Or put on a pair of certified disposable eclipse glasses — the American Astronomical Society points out there are five manufacturers that meet international standards for eclipse eye protection. They are:

When you get glasses, here’s the No. 1 thing to look for: Make sure the glasses are certified by the International Organization for Standardization (ISO). The glasses should mark that they meet “ISO 12312-2” safety standards, like so:

Complicating matters: Counterfeits that claim to be ISO-certified have been spotted. (Amazon recently issued refunds for counterfeits or uncertified pairs sold thorough its website.)

“The worst part [about the counterfeits] may be that you’re fooled into thinking that you’re protected,” Schuman says.

To avoid a counterfeit, the American Astronomical Society recommends using glasses purchased from its list of approved, definitely-not-counterfeit vendors. See that list here. You’ll want to double-check where your specs came from. If you’re in doubt, pick up a new pair (though supplies are starting to run low across the country).

If you can’t find a pair to buy, you may be able to pick up one for free at your local library. The Space Science Institute, an education nonprofit, is distributing 2 million pairs of specs to 4,800 libraries across the country. Find out if your local branch has them here. (Though a few libraries have recalled glasses too. So ask.) Also check out Vox’s sister site Curbed, which has guides for finding solar eclipse glasses in New York City and Washington, DC. Warby Parker stores are also distributing free solar eclipse glasses.

The safest way to view an eclipse: through a pinhole projector

Or if you don’t want to risk looking directly at the sun at all, try making a pinhole projector. All it takes is a piece of paper and a pin. The pinhole mimics the properties of a lens, and it will project the image of the sun onto a flat surface. The Verge has a great, thorough guide on how this all works.

One last tip: If you’re in the path of the total solar eclipse, you can take off the protective glasses the moment the moon is covering the sun 100 percent. Actually, if you don’t, you’ll miss the best part of the whole phenomenon: seeing the sun’s outer atmosphere, the corona.

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