Eye Safety During an Eclipse: Q&A With Ophthalmologist Dr. Geoffrey Hill
During an eclipse event, it is important to protect your eyes from solar damage.
On August 21st, 2017 we will get to experience the first total solar eclipse to be viewable from the Midwestern portion of the United States since 1918. A total solar eclipse occurs when the moon completely blocks our view of the sun. This is a rare event, because it only happens when the moon (which continually orbits around us on earth) passes directly between our line of sight from a particular place on earth to the sun. The moon is much closer to us than the sun, so in an eclipse it casts a shadow over the Earth during the middle of the day.
On August 21st, at around 1:00 pm those of us within the St. Louis area will see the shadow of the moon gradually moving across the sun. Shortly after 1:15 pm, the eclipse will be complete and we will have a few minutes of “night time” during the middle of the day. Depending on your location, the total eclipse may last up to two minutes and forty seconds. Here are some helpful links below to learn more about the eclipse and what to expect as it passes over the St. Louis area:
Why is it important to not look at the sun, even if it is partly obscured?
During a normal day, it is not only uncomfortable, but also dangerous to look directly at the sun. The sun is extremely bright – approximately 400,000 times brighter than the full moon – and looking directly towards its rays can lead to severe eye damage, or even permanent blindness. Sunglasses do not block enough of the sun’s energy to protect from this.
When the sun is overhead, in the middle of the day, even a few seconds of looking directly toward its rays can cause pain and eye damage. During a sunrise or sunset, the sun’s rays are traveling a much longer path through the earth’s atmosphere to reach us, causing scattering of the light rays and a reduction of the sun’s brightness from our vantage point. Therefore, it may be possible to look at the sun during a sunset – but even then, sustained gazing directly at the sun’s surface for several minutes can cause permanent damage.
A solar eclipse can be extremely dangerous, because it is tempting to look directly at the sun when the eclipse is happening. Even when the sun is partially blocked by the moon, solar damage may occur within a few seconds of gazing toward the eclipse. It is extremely important NOT to look directly at the sun with the naked eye during a solar eclipse. Furthermore, sunglasses do not provide adequate protection and may actually allow solar damage to occur faster by causing pupil dilation
What happens to your eyes when you look directly at the sun without eye protection?
Looking directly at the sun allows the sun’s visible light rays and non-visible ultraviolet rays to enter the eye. These rays of solar energy are focused by the cornea and lens of the eye directly onto the retina. This is similar to holding a magnifying glass in the sunlight and focusing the beam onto a piece of paper – it only takes a few seconds for the focused light to burn the paper. In the same way, only a few seconds of gazing at the sun or a solar eclipse, can cause the focused energy to burn the retina. This damage may be reversible, with normal vision returning after several weeks, but the longer the direct exposure to the sun’s rays, the more likely one is to sustain permanent damage.
Sustained sun gazing (or eclipse gazing) can cause keratitis (inflammation from a corneal burn), cataracts (cloudy spots in the lens of the eye), boiling of the vitreous humor that fills the eye, and retinal burns that leave behind permanent retinal holes.
How can you safely view a solar eclipse? What kind of equipment do you need?
One safe way to avoid eye damage is to simply not look directly at the eclipse. Avoiding looking directly at the sun will help to protect your eyes from damage during an eclipse.
A safe way to view the eclipse is to watch it on television or to watch a recording of the event after it is over. (While watching a recording or broadcast of an eclipse is safe, do not view the eclipse live by looking through a camera or telescope, as these lenses may actually magnify the effect of solar damage).
You can safely watch the eclipse as it happens live, by using a pinhole camera. A pinhole camera captures the image of the solar eclipse and projects it onto a small screen. Using this tool, you can see the eclipse happening on the screen while facing away from the eclipse and not looking directly toward the sun. Below are some links with instructions on how to make a pinhole camera at home:
Finally, it is possible to purchase special “eclipse glasses” made with special solar filters that can allow you to view the eclipse directly while wearing them. Specific safety instructions must be followed to use these glasses safely:
According to the NASA Eclipse Safety website, there are only five approved manufacturers of these lenses. The specific guidelines for using these lenses are also outlined in the link above. It is important not to view the eclipse with a camera, telescope, or binoculars, even while wearing certified eclipse glasses. Sunglasses, no matter how dark, are not a substitute for certified eclipse glasses and should not be used to view an eclipse.
What about when the sun is totally blocked during an eclipse?
If you happen to be in the path of totality for the upcoming eclipse – that is, if you are in an area where the eclipse will be total – there will be a brief period when the sun will be completely hidden behind the moon, and the eclipse will only be about as bright as a full moon. During this brief time, it is safe to remove your eclipse glasses and look directly toward the eclipse. Be sure to put your eclipse glasses back on or turn your gaze away before the period of totality is over and the sun is visible again. The geographic area of the path of totality for the August 21st eclipse is shown in the first link at the top of the page.
We wish you clear skies and safe eclipse viewing on August 21st!