Watching a solar eclipse? here’s how to protect your eyes

Every couple of years, a total solar eclipse occurs, during which the sun is completely blocked by the moon. If you’re lucky enough to be in the eclipse’s “path of totality,” light will fade, dusky colors will appear along the horizon, temperatures will drop, and stars and planets will come out as if it was nighttime. You’ll also be able to view the sun's corona, or outer atmosphere.

If you’re outside of the path of totality, you won't get quite the same effect. But you’ll be able to view a partial eclipse, where a chunk of the sun is blocked. You may see the lights dim or shadows take different shapes, or hear animal noises unusual for the time of day.

Catching a glimpse of an eclipse is exciting, educational, beautiful—and rare. Make the most of the occasion by using the right eye protection and following a few simple rules.

Don't look directly at the sun

Staring at the sun can cause serious, lasting injury to the eye, and even blindness. And though this may sound like well-worn advice, many ignore it during eclipses. After one 1999 event in England, for example, at least 14 people reported significant damage to their eyesight. Thousands more phoned into hotlines or visited clinics for vision problems.

Over the course of a total solar eclipse, you can only look straight at the sun when it's fully blocked—not before, and not after. When not completely covered, its rays are able to penetrate and literally burn your eyes. It can alter your vision, maybe for good.

Wear protective glasses

Whether you're waiting for totality or looking at a partial eclipse, you must protect your eyes. Skip the sunglasses, which aren't nearly strong enough, and opt for eclipse glasses. Their lenses have a special type of solar filter, making them thousands of times darker than your favorite pair of shades. The American Astronomical Society keeps a list of reputable vendors. Order only from approved companies, since fake glasses often flood the market in the weeks before an eclipse. Inspect your pair before using them, too. Damaged glasses should be thrown away, as should those more than three years old that don't meet current standards.

Another way to see an eclipse: a pinhole camera, which you may remember constructing in elementary school. These do-it-yourself devices—often created from paper, shoeboxes, tin foil, your fingers, or even a tree—allow you to look at the eclipse indirectly via a projection. Look for instructions online.

Beware of unfiltered lenses

For a better view of the eclipse, you may want to use your camera, a telescope, or a pair of binoculars. Avoid the temptation, however. The lenses in these optical devices actually concentrate the sun's rays, making them even worse for your vision. Donning your eclipse glasses before gazing through your binoculars won't help you, either; they don't provide enough protection.

Still, eclipses are reportedly best seen up close. So, if you decide to use a magnifying tool, look for special solar filters made for your particular device. They're relatively inexpensive and widely available online. Before the eclipse, make sure the filter fits tightly, and there are no scratches. During the event, when you're not using your filtered camera or telescope, remember to wear your eclipse glasses.

A total solar eclipse may be once-in-a-lifetime experience. Make sure you're able to see its full celestial beauty—and still see other things afterward—by taking the right safety measures.