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How to Safely Watch a Solar Eclipse

Eclipse Travel Guide

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Looking directly at the everyday Sun is unsafe. It can be blinding – literally. We all instinctively know that. If you do more than glance at the Sun, you’ll find yourself squinting, your eyes will start watering, and you’ll quickly look away. Your eyes are not made to deal with intense light. But during a solar eclipse and total solar eclipse, you want to look at the Sun. You want to follow the progress of the Moon across the Sun’s face. It’s possible, but only if done in a safe manner.

A Significant Danger

Improper solar eclipse viewing can result in what’s known as eclipse blindness. Even a brief exposure of the eye’s retina (the thin layer of tissue lining the back of the eye) to the Sun’s intense light will result in damage to the eye’s light-sensitive rod and cone cells. This retinal damage may be accompanied by a thermal injury. The high level of radiation causes heating that literally cooks the eye and destroys the rods and cones. The consequence is a loss of vision that may be either temporary or permanent, depending on the severity of the damage. While all this is taking place within your eye, you won’t feel a thing, because there are no pain receptors in the retina. Even worse, the visual effects are typically not noticeable until hours after the damage is done.

Indirect Viewing

To follow the progress of a solar eclipse, it must be safety first. And the safest way to view the partial phases of a solar eclipse is to not look directly at the Sun at all. If you’re observing from home, head to your kitchen, bring out a colander or slotted spoon, and hold it over white paper or pale concrete. Amazingly, the little holes project solar crescents onto the ground. This also works with fingers. Cross the outstretched, slightly open fingers of one hand over the outstretched, slightly open fingers of the other. Stand with your back to the Sun and look at the shadow of your hands on the ground. The little spaces between your fingers will project a grid of small images, showing the Sun as a crescent. If your observing site has leafy trees, look at the shadows of leaves on the ground. During the partial eclipse, the tiny spaces between the leaves will act as pinhole projectors, dappling the ground with images of the crescent Sun!

looking at the sun
Left: Light filters through a colander to project numerous crescent-sun images on the ground (Photo by Joy Ng/NASA). Right: A safe solar-eclipse viewer made from a cereal box (Photo by Mary Pat Hrybyk-Keith/NASA).

Pinhole Projection

Speaking of pinhole projection, that’s another way to look at the solar eclipse safely. There are lots of how-to examples on the Internet. A typical instruction might be this: Pass sunlight through a small hole punched in an index card, and project an image of the Sun through it onto a nearby white surface. (Do not look at the Sun through the pinhole!) The problem with this example, and others like it, is that the image is usually dim and washed out by the ambient daylight; it’s a very disappointing sight.

With just a little work, you can make a superior pinhole projector using a box. The idea is to project the solar disk onto the inside of a mostly closed box so there is less ambient light surrounding the image, making it easier to see. Another advantage is that you have your back to the Sun, so there’s no temptation to peek directly at the eclipse. The downside is that only one person at a time can see the projected image. Here are three links to help you make such a projector: Using a cereal box (NASA); using a larger box (George Eastman Museum); and a website with instructions and photos.

Direct Viewing

If you feel you need to look directly at the Sun to follow the partial eclipse, you must shield your eyes using a safe, special-purpose solar filter. Unfortunately, there is an almost limitless variety of handy materials that will dim the Sun significantly but are nevertheless unsafe and dangerous. Never look using CDs, CD-ROMs, DVDs, color and black-and-white film, film negatives with images on them, sunglasses (single or multiple pairs, polarized or not), photographic neutral density filters, or polarizing filters. All are hazardous. All will dim the Sun to some degree but not nearly enough to protect your eyes. Just because the Sun appears dim doesn’t mean the filter is safe, so do not use any homemade filters.

special purpose solar filters
Shade #14 welder’s filter mounted in a cardboard holder. Inset: The view through the filter (Photo by Rick Fienberg/TQ).
Eclipse glasses and Partial inset
Special eclipse glasses provide a safe solar view. Inset: The view through eclipse glasses (Photo by Paul Deans/TQ).

So what can be used to view solar eclipses? One widely available filter that is safe for solar eclipse viewing is a shade number 14 welder’s glass (also available in plastic), which can be obtained from welding supply outlets. Welder’s glass/filters provide excellent quality for visual observation, and shade #14 is perfectly safe. Shade #12 is also safe, but many people find the Sun uncomfortably bright when using this filter. Shade #13 is a good compromise but is not as widely available as shades #12 and #14. Do not use any lower shade number of welder’s filter, and don’t combine two shades of welder’s glass with lower numbers. In addition to welding supply stores, shade #14 welder’s filters, conveniently mounted in sturdy corrugated holders, are available from Rainbow Symphony.

During the Great American Eclipse of 2017, many people used eclipse ‘glasses’ to watch the Moon slide across the Sun’s face. Most of these eclipse ‘glasses’ are stiff paper frames with safe solar-filter material in place of lenses. The frames have arms that fit over your ears, and they sit on the bridge of your nose close to your eyes. If you need regular glasses for distance viewing, you can adjust the paper frames to fit over the front of your glasses. Because they are lightweight, and because the solar-filter material can be scratched, these eclipse ‘glasses’ need to be handled with care. Always inspect the filter material before use; if it’s scratched, punctured, torn, or otherwise damaged, discard the eclipse ’glasses.’ Read and follow any instructions printed on, or packaged with, the eclipse ‘glasses.’ The American Astronomical Society has a webpage devoted to safely watching a solar eclipse, with a link to reputable vendors of solar filters & viewers. There, the links under ‘Solar Viewer Brands’ will go to companies that sell eclipse glasses, whether or not a solar eclipse is imminent.

One final caution. Welder’s filters and eclipse shades/glasses are never to be used with optical equipment of any kind. They are for viewing solar eclipses with only your eyes, and must never be used in combination with cameras, binoculars, or telescopes. Optical gear magnifies the Sun’s light, and neither welder’s filters nor eclipse glasses are designed to withstand the intensity of magnified sunlight. Glass solar filters will shatter, the material in eclipse viewers will melt, and your eyes will likely suffer damage.

Image header by Mark Margolis/Rainbow Symphony

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