Millions of people will soon travel to a narrow strip in America to witness a rare event: a total solar eclipse. On 21 August, many will look up to the sky to witness this phenomenon – will you be one of them? In the following shortened excerpt from Totality: The Great American Eclipses of 2017 and 2024, learn what types of eyewear you should be using to watch the Sun disappear, when you can do away with eye protection completely, and other ways to best view this event.
You would never think of staring at the Sun without eye protection on an ordinary day. You know the disk of the Sun is dazzlingly bright, enough to permanently damage your eyes. Likewise, any time the disk of the Sun is visible—throughout the partial phase of an eclipse—you need proper eye protection. Even when the Sun is nearing total eclipse, when only a thin crescent of the Sun remains, the 1% of the Sun’s surface still visible is about 10,000 times brighter than the full moon.
Once the Sun is entirely eclipsed, however, its bright surface is hidden from view and it is completely safe to look directly at the totally eclipsed Sun without any filters. In fact, it is one of the greatest sights in nature. Here are ways to observe the partial phases of a solar eclipse without damaging your eyes.
Solar eclipse glasses
The most convenient way to watch the partial phases of an eclipse is with solar eclipse glasses. These devices consist of solar filters mounted in cardboard frames that can be worn like a pair of eyeglasses. If you normally wear prescription eyeglasses, you place the eclipse glasses right in front of them.
When you are using a filter, do not stare for long periods at the Sun. Look through the filter briefly and then look away. In this way, a tiny hole that you miss will not cause you any harm. You know from your ignorant childhood days that it is possible to glance at the Sun and immediately look away without damaging your eyes. Just remember that your eyes can be damaged without you feeling any pain.
Another safe filter for looking directly at the Sun is welder’s goggles (or the filters for welder’s goggles) with a shade of 13 or 14. They are relatively inexpensive and can be purchased from a welding supply company. The down side is that they cost more than eclipse glasses and give the Sun an unnatural green cast.
The pinhole projection method
If you don’t have eclipse glasses or a welder’s filter, you can always make your own pinhole projector, which allows you to view a projected image of the Sun. There are fancy pinhole cameras you can make out of cardboard boxes, but a perfectly adequate (and portable) version can be made out of two thin but stiff pieces of white cardboard. Punch a small clean pinhole in one piece of cardboard and let the sunlight fall through that hole onto the second piece of cardboard, which serves as a screen, held behind it. An inverted image of the Sun is formed. To make the image larger, move the screen farther from the pinhole. To make the image brighter, move the screen closer to the pinhole. Do not make the pinhole wide or you will have only a shaft of sunlight rather than an image of the crescent Sun. Remember, a pinhole projector is used with your back to the Sun. The sunlight passes over your shoulder, through the pinhole, and forms an image on the cardboard screen behind it. Do not look through the pinhole at the Sun.
Solar filters for cameras, binoculars, and telescopes
Many telescope companies provide special filters that are safe for viewing the Sun. Black polymer filters are economical but some observers prefer the more expensive metal-coated glass filters because they produce sharper images under high magnification.
Caution: Do not confuse these filters, which are designed to fit over the front of a camera lens or the aperture of a telescope, with a so-called solar eyepiece for a telescope. Solar eyepieces are still sometimes sold with small amateur telescopes. They are not safe because they absorb heat and tend to crack, allowing the sunlight concentrated by the telescope’s full aperture to enter your eye.
Do not use standard or polaroid sunglasses to observe the partial phases of an eclipse. They are not solar filters. Standard and polaroid sunglasses cut down on glare and may afford some eye relief if you are outside on a bright day, but you would never think of using them to stare at the Sun. So you must not use sunglasses, even crossed polaroids, to look directly at the Sun during the partial phases of an eclipse.
Do not use smoked glass, medical x-ray film with images on them, photographic neutral-density filters, and polarizing filters. All these “filters” offer utterly inadequate eye protection for observing the Sun.
Observing with binoculars
Binoculars are excellent for observing total eclipses. Any size will do. Astronomy writer George Lovi’s favorite instrument for observing eclipses was 7 x 50 binoculars—magnification of seven times with 50-millimeter (2-inch) objective lenses. “Even the best photographs do not do justice to the detail and color of the Sun in eclipse,” Lovi said, “especially the very fine structure of the corona, with its exceedingly delicate contrasts that no camera can capture the way the eye can.” He felt that the people who did the best job of capturing the true appearance of the eclipsed Sun were the 19th century artists who photographed totality with their eyes and minds and developed their memories with paints on canvas.
For people who plan to use binoculars on an eclipse, Lovi cautioned common sense. Totality can and should be observed without a filter, whether with the eyes alone or with binoculars or telescopes. But the partial phases of the eclipse, right up through the diamond ring effect, must be observed with filters over the objective (front) lenses of the binoculars. Only when the diamond ring has faded is it safe to remove the filter. And it is crucial to return to filtered viewing as totality is ending and the western edge of the Moon’s silhouette brightens with the appearance of the second diamond ring. After all, binoculars are really two small telescopes mounted side by side. If observing a partially eclipsed Sun without a filter is quickly damaging to the unaided eyes, it is far quicker and even more damaging to look at even a sliver of the uneclipsed Sun with binoculars that lack a filter.
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