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Urgent Safety Bulletin

by Howard L. Cohen
On February 26, 1998 the shadow of the Moon will pass from the Pacific Ocean over northern South American and cross the Caribbean. Eye safety is important for this event but public warnings are often dangerously wrong.

Warning! Reading Better Homes and Gardens may be dangerous to your health! This popular monthly magazine publishes a column, "The REAL Truth About Health Myths." Unfortunately, the REAL truth in their January 1998 issue in no truth at all. In fact, this issue gives information that is not only misleading but can also have very serious health consequences for readers who take the column's advice literally. January's health column leading feature, "If you look at a solar eclipse, you'll go blind," begins with the statement:

"This simple, yet terrifying saying sounds too extreme to be real, but is no fable. Staring at the brightest light source in our solar system—even during an eclipse—can partially blind a person temporarily or forever."

This passage is true but also misleading.

The True Part: The Sun, when not covered by the Moon, or when partially covered during a partial solar eclipse, is very dangerous to look at unless proper precautions are taken. However, contrary to popular myth, the Sun does not suddenly begin to emit powerful, damaging rays when it goes into eclipse! The Sun is dangerous to look at whether in eclipse or not, as long as even a slim crescent of sunlight remains. But read on.

The Misleading Part: The Sun, when completely hidden during the total phase of a total solar eclipse, is not dangerous to look at! This is the only time when it is completely safe to look in the direction of the Sun. In fact, one should look at the totally eclipsed Sun. To do otherwise would be to one miss one of the most awesome, beautiful and inspiring sights nature has to offer—an opportunity that rarely comes to most individuals.

The article continues with:

"When viewing a solar eclipse, always protect your eyes with dark glasses and peep through a piece of paper pierced with a pin."

Wrong! Wrong! Wrong! And very dangerous advice. Filters, even if dark, may transmit invisible infrared and ultraviolet radiation that can seriously damage the eye's retina. Filters that should not be used include sunglasses (no matter how dark), smoked glass, typical neutral density photographic filters, CD's, floppy disks (plastic case removed), Mylar food packaging, color negatives or slides, and certain black and white films. The latter include any silverless (chromegenic) black and white films, any film with images including X-ray film, and any undeveloped film. Although making a safe, solar viewing filter is possible from fully exposed and developed silver-based black and white film, most people should not try to do this if they do not fully understand what they are doing.

Another warning. Solar viewing filters that come with some telescopes and made to fit over the telescope's eyepiece are also very dangerous. These filters may crack from the Sun's rays that the telescope's optics concentrate on the filter. This concentrated light will instantly burn the eye's retina. Throw this type of filter away!

Several reputable companies manufacture safe solar viewing filters. (See references at end of article.) However, for most people who want to view the Sun, either out of eclipse or in partial eclipse, the best method is a simple pinhole projection system.

The Better Homes and Gardens advice to "peep through a piece of paper that has been pierced with a pin" is wrong, wrong, wrong! Never look at the uneclipsed or partially eclipsed Sun through a pinhole! The sunlight passing through the pinhole may still damage your eyes. Pinhole devices, however, can be safely used to project the Sun's image. The observer views the projected image and not the Sun itself! For example, punch a small pinhole in an index card. Stand, facing away from the Sun, and use the pinhole in the card to project a small image of the Sun onto another index card a few feet away. More sophisticated "pinhole cameras" (as they are often called) can be made, but even this simple device will work and is safe to use.

On February 26, 1998, More than half the United States will experience a solar eclipse. In the United States and Canada people south and east of a curved line running from extreme Southern California through Lake Michigan and Newfoundland will see a partial solar eclipse. The solar eclipse will be total for people who lie within a long, narrow path running from the Eastern Pacific Ocean, along the northern coastline of South America and into the Caribbean Sea. (Most cruise ships no longer have space for this event.) Only people in the path of totality can view the Sun safely with no protection, but only during the few minutes of total eclipse. However, even these fortunate people should use safe viewing procedures when the Sun is out-of-eclipse or during the partial phases.

References

Chou, Ralph B., "Eye Safety And Solar Eclipses," in NASA Reference Publication 1398, April 1997, p. xx. (Web adaptation at http://planets.gsfc.nasa.gov/eclipse/safety2.html)
Chou, Ralph B., "Solar Filter Safety," in Sky and Telescope, February 1998, pp. 36–40.
Espenak, Fred, "Eye Safety During Solar Eclipses," in NASA Reference Publication 1383, April 1996, p. 17. (Web adaptation at http://planets.gsfc.nasa.gov/eclipse/safety.html)

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