For approximately 2 to 3 hours on Monday, August 21, 500 million people across a large portion of North America will experience a rare phenomenon—a total solar eclipse.
It’s been nearly 40 years since the United States was in the path of a total solar eclipse; people are paying exorbitant amounts in airfare and lodging to be in the path of totality—the few precious minutes in which the moon will completely block the sun.
In the United States, the path of totality will pass through 12 of the 48 contiguous states (see the map below).
Because California is not directly in the path, residents of the Golden State will experience a partial eclipse. Some parts of Northern California are expected to experience between 75%–85% totality, while Southern California is expected to experience between 55%–70% totality. The only safe way to look directly at an eclipsed or partially eclipsed sun is through special-purpose filters, not with sunglasses or the naked eye.
Wherever you are, the National Aeronautics and Space Administration (NASA) stresses that looking directly at the sun is unsafe except during the brief total phase of a solar eclipse (“totality”) when the moon entirely blocks the sun’s bright face, which will only happen within the narrow path of totality.
Eye care professionals agree that even if you take several quick glances up at the sun during a partial eclipse, it can cause damage to the retina (the light sensitive tissue at the back of the eye). Sunlight can burn and potentially scar the retina, which is called solar retinopathy or photic retinopathy. The retinal damage would not be noticeable immediately because the light-sensitive cells in the eye can continue working for several hours before becoming inoperative, ultimately leading to temporary or permanent vision loss.
Should there be a cloudless sky and you’re able to take a few minutes out of your day to witness the eclipse, here are several ways you can view it safely, courtesy of The American Optometric Association and NASA:
- Use approved solar eclipse viewers. The only safe way to view a partially eclipsed sun is through special-purpose solar filters, such as “eclipse glasses” or viewers that meet international standard ISO 12312-2 for safe viewing. Sunglasses, smoked glass, unfiltered telescopes or magnifiers and polarizing filters are unsafe. If you can’t find eclipse viewers, build a pinhole projector/camera to watch the eclipse. Lastly, inspect your solar filter before use; if it is scratched or damaged, discard it. Always supervise children using solar filters.
- Before looking at the sun, cover your eyes with the eclipse viewers while standing still. Glance at the sun, turn away and then remove your filter. Do not remove the filter while looking at the sun.
- Only within the path of totality-and only once the moon completely blocks the sun can eclipse viewers safely be removed to view totality. Once the sun begins reappearing, however, viewers must be replaced. This will not apply to those viewing in California because we are not in the path of totality and it will never be safe to view the partial eclipse without a solar viewer.
- Do not look at the sun through a camera, a telescope, binoculars, or any other optical devise while using eclipse glasses or hand-held solar viewer—the concentrated solar rays will damage the filter and enter your eye(s), causing serious injury.
- If you normally wear eyeglasses, keep them on. Put your eclipse glasses on over them or hold your handheld viewer in front of them.
Be on the lookout for unscrupulous in-store and online vendors selling unapproved protective solar filters and viewers manufactured by non-reputable vendors. NASA and the American Astronomical Society urge the public to look for products that carry the international safety standard number ISO 12312-2.
Finally, if you should experience discomfort or vision problems following the eclipse, visit the website of the California State Board of Optometry for a list of licensed professionals for a comprehensive eye examination.