Photograph by Maynard Owen Williams, National Geographic

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People watch a solar eclipse through smoked glass or film on Japan's Rebun Island in 1949.

Photograph by Maynard Owen Williams, National Geographic

How to Safely Watch a Solar Eclipse

Soak up these safety tips for skywatchers wanting to take in the beauty of a solar eclipse.

We've all heard the warnings before: Looking directly at the sun, whether it's with your naked eyes or through an optical aid, can be extremely dangerous.

This holds true on any regular sunny day—and when there is a partial solar eclipse. However, there are easy, safe ways to soak in the sun’s great disappearing act.

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For the fleeting few minutes during a total eclipse when the entire disk of the sun is completely covered by the moon’s silhouette, it is completely safe to look directly at it with your naked eyes.

However, during an annular ("ring of fire") eclipse or a partial eclipse—where only a portion or even a tiny bite appears to be taken out of the solar disk—it is always extremely dangerous to look at the sun directly.

While viewing a total eclipse is safe, it’s important to be aware of when it ends and when the sun starts its return.

Don't Stare at the Sun

Even if only a tiny sliver of the sun can be seen, it's too bright for our eyes. Less than 1 percent of the visible sun is still 4,000 times brighter than the full moon.

The retina of an unprotected eye can burn in as little as 30 seconds. It is particularly dangerous to use binoculars or a telescope to look at the sun. A retinal burn in that case can be frighteningly fast—taking no more than a fraction of a second.

And what makes it even more scary is that because the retina of the eye lacks pain receptors, you won't feel it happening. And the effects may not appear until hours after the damage has been done.

Use Approved Filters

Many materials and methods popularly used to observe an eclipse may be unsafe. Smoked glass, x-ray films, sunglasses, and camera filters, for example, are all dangerous and should be avoided completely.

That's because while they reduce the incoming visible light, they fail to stop the full force of the sun's hazardous infrared and ultraviolet radiation.

Despite the warnings, there are plenty of ways to safely enjoy one of Mother Nature’s most amazing spectacles.

Mylar Filters

Major telescope manufacturers sell aluminum-coated mylar plastic sheets that are available as eclipse viewing glasses or as ring filters that fit over the front of telescopes. These coated filters render the sun in steely blue-white color.

Forget about using those Mylar space blankets sold at camping stores; they are way too thin and flimsy, letting in dangerous amounts of strong light.

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Welders Glass

For those with more experience with solar viewing who want to catch the partial phases of an eclipse, a number 14 arc welder’s glass can work well. The rectangular piece of dark green glass filters out all ultraviolet and infrared radiation and reduces visible light by a factor of at least 300,000.

The only problem with this method is finding a handy local welder’s supply store when you need it.

Telescope Glass Filters

The best way to see the eclipse unfold up-close is by using metal-on-glass filters that fit on the front end of binoculars and telescopes.

Commonly available at local and online astronomy stores, these filters provide a safe, pleasing orange-yellow hue and are great to use for photography and sunspot viewing as well.

Pinhole Projection

By far the safest method of watching the sun anytime, even during an eclipse, is to avoid gazing at the spectacle directly at all but instead look at a projected image of the sun. A simple pinhole camera can do the trick.

To make one, poke a three-millimeter-wide (or thereabouts) pinhole into a square piece of cardboard paper. Then, with the sun behind you, project the sun through that hole onto another white piece of paper. Now you can safely view the projected image of the sun on that second piece of paper.

Remember never to look through the pinhole directly at the sun.

Notes for Astronomers

While it is possible to project an image of the sun through telescope optics onto a paper, it can damage your instrument. The sunlight can heat up optics in just a few minutes, damaging eyepiece coatings and even melting the cement that holds eyepiece optics together.

Also avoid so-called solar eyepieces that may come with less expensive telescopes. They are highly dangerous, as intense heat from incoming unfiltered sunlight can hit the eyepiece and cause the lens to crack, allowing the magnified sunlight to hit your eye.

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