How to Safely Watch a Total Solar Eclipse

How to Watch a Solar Eclipse

June 24, 2019
Total Solar Eclipse
NASA

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You can seriously damage your eyes by watching a solar eclipse without proper protection (NOT sunglasses!). Here is information on how to watch an eclipse safely and what kind of eye protection you need—from eclipse glasses to welder’s googles.

First, if you are watching a “total solar eclipse,” do you realize that you can only see totality from a very limited area—the narrow ribbon of darkness? Otherwise, a partial solar eclipse will unfold for you. (Learn about different types of eclipses.) You can NOT safely look at any of it. Not even for a minute. You need eye protection.

But if you are watching from that narrow dark band of the full eclipse, well, that awesome, unbelievable spectacle does not require special filters during those two minutes of totality. Still, the mind-numbing glory of totality is presaged and then followed by an hour-long partial phase—and here also you must protect your vision.

Is It Safe to Look at the Sun?

I’m in touch with a man who suffers permanent eye damage from looking straight at the Sun decades ago. True, he used binoculars, which can cause permanent blindness in just a second or two. 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.

Is It Safe to Look at a Total Solar Eclipse?

So 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.

NEVER use sunglasses of any kind, smoked glass, or anything but special eclipse glasses or a Sun filter.

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. 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.

 

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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.

Purchase Welders’ Goggle Filters

If you do not have access to a solar filter, you may use instead what is called welder’s glasses, rated 14 or higher. They are available in most local hardware stores.

For the seven total eclipses I’ve led for our tour company, we always purchase welders’ goggle filters. Their optically certified glass allows for a crisp, perfect image, and those filter replacements are only about $2.  

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Also, don’t use the stuff that was popular between 1870 and 1960, such as smoked glass and reflections from puddles. Exposed and developed film was once universally used. In truth, two layers of exposed and developed black and white (not color) film, meaning those black strips accompanying negatives, are adequate, and many science tours used them right through the 1980’s. Still, I’d limit the peeks to quick glimpses through them. With eyesight, you want to be conservative.

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!

Learn even more about solar eclipse eye safety.

About This Blog

Welcome to “This Week’s Amazing Sky,” the Almanac’s hub for everything stargazing and astronomy. Bob Berman, longtime and famous astronomer for The Old Farmer’s Almanac, will help bring alive the wonders of our universe. From the beautiful stars and planets to magical auroras and eclipses, he covers everything under the Sun (and Moon)! Bob, the world’s mostly widely read astronomer, also has a new weekly podcast, Astounding Universe

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