Solar Eclipse Safety: How to Protect Your Eyes

Do Not Look at the Partial Eclipse

The “partial” eclipse is the hour-long prologue to a total solar eclipse. You can NOT safely look at any of it. Not with sunglasses, not with binoculars, not through a camera lens, and not through a telescope. Not in any way except with a special-purpose solar filter secured over the front of the optics.

Even when 99% of the Sun’s surface (the photosphere) is obscured during the partial phases of a solar eclipse, the remaining crescent Sun is still intense enough to cause a retinal burn, even though illumination levels are comparable to twilight. Failure to use proper observing methods may result in permanent eye damage or severe visual loss. Most individuals who sustain eclipse-related eye injuries are children and young adults.

Technically, the only time that the Sun can be viewed safely with the naked eye without special filters is during those few minutes of totality when the Moon completely covers the disk of the Sun. That said, you will also need eye protection during the hour-long partial eclipse that follows totality.

Also: It should be said that most people will never see totality because they don’t realize that you can ONLY see that unbelievable spectacle from a very limited area—the narrow ribbon of darkness. (See the map of the 2024 eclipse path of totality.) For most people, a partial solar eclipse will unfold.

Never risk your eyesight. As my book Zapped makes clear, solar radiation includes fascinating components like ultraviolet waves. Even normal lifetime exposure to solar UV ages the eye’s outer layers and is responsible for cataracts. But right now we are concerned about the immediate damage produced by looking directly at the sun without adequate eye protection. 

Pull up a chair: there’s a lot of misinformation out there.

What Happens If You Look at a Solar Eclipse?

I’m in touch with a man who suffers permanent eye damage from looking straight at the Sun decades ago. NOTE: He used binoculars, which is the first lesson. This can cause permanent blindness in just a second or two. He forwarded me his eye doctor’s report. This photochemical injury occurred mainly when the retina is exposed to the blue and green components of sunlight.

It’s why people who routinely wear sunglasses in everyday life are wisely protecting their eyes. That said, sunglasses are totally inadequate shielding for looking directly AT the Sun. There, the greatest danger comes from deep reds and invisible near-infrared radiation, which is absorbed by the dark pigment below the retina, where it heats up the tissue so much that it can literally cook and destroy retinal cells, leaving a permanently blind area. This thermal damage causes no pain, since there are no pain receptors in the retina. In fact, you won’t experience the visual damage until at least several hours later.

This is why staring at the sun is so bad. The heat in the retina builds up. That’s why—although everyone has taken quick glimpses at the Sun during their lives without any harm—staring at the sun is dangerous. And that’s just what a solar eclipse makes people do.

But it brings up that ancient eclipse question: what is the actual, unexaggerated danger of simply peering at the Sun directly?

Few articles tell the truth because eyesight is so precious; editors usually feel it’s better to exaggerate the danger than to state it neutrally. Years ago when I was with Discover magazine and researched this, the shortest amount of Sun-staring I could find, that had created a permanent detectable retinal lesion was 30 seconds. That was a man who’d been drinking, who’d stared at the Sun on a bet. Going the other way, we’ve all taken quick looks at the Sun during our lives, and have not suffered eye damage. So those are the starting points, the limits: A quick fraction-of-second glance won’t harm you, while 30 seconds can damage your retina permanently. In between lies a blurry dangerous realm, a terra incognito of ill-defined peril, a swampy land you want to avoid.

And contrary to widespread myth, the Sun is not more dangerous when it’s in eclipse. It’s simple. That’s when people have a motive for staring at it. In reality, the danger is produced by heat concentrated on the retinal cells. It takes this heat a little bit of time to build up.

Can You Look During Totality?

So, we established that it is not safe to look directly at the Sun without specialized eye protection for solar viewing, except during the brief total phase of a total solar eclipse.

What about totality? Let’s picture the real-time scenario, the quandary. It’s eclipse day. The Sun has been moving behind the Moon for the past 50 minutes. Soon, the Sun will appear as a thin sliver, like a slender crescent Moon. In a minute, even this gets reduced in size. You look at the ground around you; it’s getting darker. If you are within the path of totality, you want to see the famous “diamond ring” that happens just before totality begins. Is it okay to then take a quick squinting glimpse at the Sun?

Some articles say no. But I and other astronomers, including NASA solar system ambassador Charles Fulco, always do. When it’s almost total, we’ve taken quick (no more than a half second) glimpses up. If we see anything but the start of totality, we immediately look away. If you can be disciplined enough to limit such momentary glimpses to under a half second, you’ll be okay.

But many don’t have such discipline. And children should never be allowed to try. So the safest route is to play it safe, and use your eye protection until darkness when the Sun is totally eclipsed or the expert in your party shouts, “It’s total now!”

Types of Solar Eclipse Eye Protection

What type of eye protection is best? Here are a few options for most of the viewers on eclipse day—enthusiastic beginners.

Eclipse Glasses

Many companies sell inexpensive “eclipse glasses” made of cardboard, with plastic Mylar filters. They work. The cardboard types run about $10 for a 4-pack. 

Beware of fake, knock-off eclipse glasses; they may not be strong enough to fully protect your eyes. You can test your glasses by simply looking through them. If you’re able to see light from lamps, headlights, or even reflections of the sun, your glasses are not strong enough! You should only be able to see the sun itself through your glasses. 

The American Astronomical Society has compiled a list of vendors where you can buy safe eclipse glasses.

If you’re feeling fancy, go for plastic frames which are sturdier versus cardboard.  Do not even consider regular sunglasses. Wear the solar shades right until the Sun goes completely behind the Moon.

Make a Pinhole Viewer

Some people punch a pinhole in a box and let the Sun project its eclipsed image on another interior part of the box. That’s always safe because you’re not looking directly at the Sun. See NASA’s guide on how to make a pinhole camera.

Welders’ Goggle Filters

The cheap commercial eclipse filters made of mylar plastic are fine. But I’ve always preferred welding filters because of their superior optical quality. They are available in most local hardware stores.

For the seven total eclipses I’ve led for our tour company, we always purchase these filters. Their optically certified glass allows for a crisp, perfect image, and those filter replacements are only about $2. But if you go to a welding supply store, you must buy shade 12, 13, or 14—and nothing else. A 14 will be the most comfortable, although a shade 12 is definitely still safe, web misinformation notwithstanding.

Eclipse Glasses Alternatives

If you’ve not bought any welding goggles or eclipse glasses and are desperate on eclipse day, all may not be lost. You can ask your Welding supply store to create a 12, 13, or 14 shade by cobbling together a few lighter-shade filters and stacking them. 

Or, you can create a safe filter by looking through two layers of exposed and developed black and white film. It’s what many astronomers used to use, and has been well tested. Those are the inky black strips at the very end of negatives. But don’t try to look through negatives with images on them. And don’t use color film. And don’t use black and white film unless it’s been exposed and developed. Even then, use a doubled up layer. Two thicknesses. We’re talking about old fashioned Kodak products like Plus-X and Tri-X, which contain the silver granules that block harmful light. Some newer films don’t have the silver, so only use the older negative strips—the ones you’ve had lying around since forever.

Our grandparents used to hold a piece of glass over a candle flame and let it get black from soot. Was that dangerous? Were they endangering their eyesight? Surprise: Modern testing shows that such smoked glass only transmits 0.0032 percent of the Sun’s visible and invisible radiation. So it WAS adequate for solar viewing.  Nonetheless, to slightly paraphrase our parents, “Please don’t smoke glass.” You should avoid it because you never know how deep the soot layer is or whether some of it has smudged off. And definitely avoid such dangerous web suggestions as looking through a CD disk. The Sun’s image may seem safely dim, but too much infrared (heat) may be arriving on your retina.

What About Binoculars?

The most dangerous is a view through an unfiltered telescope or binoculars. So if you’re observing totality through binoculars, that’s great. But I’d limit it to the middle section of this short totality. Once you’ve passed the eclipse midpoint, about a minute after the start of totality, I’d put down the binoculars. Because the last thing you want is for totality to suddenly end with, say, a diamond ring of full sunlight, and for you to be still using that instrument. Don’t let that happen.

Taking Photos of the Eclipse

Do not look at the Sun through a camera without a special solar filter—nor while using your eclipse glasses or solar viewer. The concentrated solar rays will damage the filter and enter your eye(s), causing serious injury. Even if you buy a special solar filter for your camera, shooting an eclipse is challenging, requiring the photographer to shift from too much light to shooting in the dark when you need a fast lens. If you’re a beginning photography, we’d put the camera down during the 2-minute event, soak in the experience, and look at the thousands of photos taken by professionals after the event.

We want to see this eclipse, and also be able to see each other afterward!