Experience America’s 2017 Solar Eclipse
On the afternoon of August 21, 2017 millions of people across the United States will be able to observe an amazing spectacle of nature – a total solar eclipse. During a solar eclipse, the moon passes between the Sun and the Earth, casting its shadow on the Earth.
During a total eclipse, daytime becomes deep twilight and the Sun’s corona can be seen glowing in the darkened sky. It is a beautiful event to behold, but potentially blinding if not done safely.
Staring at the sun for even a very short time can cause permanent damage to the retina, usually in the fovea, the most sensitive part of the retina that is responsible for central vision and our ability to see fine detail. Therefore, it is not safe to view an eclipse with the naked eye. Many people have been blinded by directly staring at the sun. Thankfully, for those who are fascinated by all things astronomical, there are several ways that you can safely view this spectacular astronomical event.
Before discussing proper viewing of solar eclipse, let’s review all the ways that are absolutely not safe to view a solar eclipse. NEVER, NEVER look directly at the sun, either with the naked eye or through telescopes, binoculars or camera lenses. Even using Baader Planetarium’s AstroSolar Safety Film does not make for safe viewing with the eye. They are only meant as aperture filters for those optical devices and are not safe for direct viewing of the sun with your eyes.
It is also not safe to use the homemade filters you may have heard about. Dark sunglasses, neutral density or polarizing camera filters, smoked glass, exposed camera film, space blankets, potato chip bags, DVDs or any other materials you may have heard about are not safe for looking at the sun. These homemade filters may seem like they dim the sun to a comfortable level, but they do not do so across the whole electromagnetic spectrum. Just because they may make it comfortable to look at the sun, does not mean they are blocking solar infrared radiation. While it may be a comfortable view, the sun’s IR rays are damaging your retina. And because there are no pain receptors in the retina, you will not know until you notice the blind spots have developed that you have made a tragic mistake. To repeat, do not use homemade filters to look at the sun!
So what are the safe ways to view a solar eclipse?
A very cheap way is through indirect viewing by the use of pinhole projection. You don’t need any materials more expensive than your hands. With your back to the sun, cross your outstretched, slightly open fingers of one hand with the slightly open fingers of the other hand to make a grid of small openings between your fingers. Then look at the shadow of your hands and you will see a grid of small images of the eclipse on the ground. Another way is to have two sheets of paper. Use a tack or pin to make a perfectly round hole in one sheet and then project the image of the eclipse onto the other sheet with the pinhole you just made.
Of course, indirect viewing is not as impressive as directly viewing the eclipse. The only safe way to do that is with the use of special purpose solar filters such as eclipse glasses or handheld viewers made specifically for this purpose. These filters must meet the ISO 12312-2 international standard for such products. To date, 5 manufacturers have certified that their products this standard: Rainbow Symphony, American Paper Optics, Thousand Oaks Optical, and Baader Planetarium. These viewers are very inexpensive and can be purchased online.
Make sure to inspect your filters to make sure they are not scratched or damaged. If they are, do not use them. Make sure to read and follow the directions printed on the filters. Also be sure to supervise any children who will be using them. Be sure to cover your eyes with the filters BEFORE you look at the sun. And make sure to look away from the sun before removing the filters.
A solar eclipse is one of nature’s most amazing spectacles. If you follow these simple guidelines, you can safely view one and enjoy a memory of a lifetime!
Dr. James Grove