Ask the Expert: Protecting your eyes during a solar eclipse
Oct 11, 2023
An annular solar eclipse, where the moon partially covers the sun, will pass over the United States on Saturday, Oct. 14. Those living in Indiana will experience it as a partial solar eclipse, where just about 50% of the sun will be covered by the moon.
Hin Cheung. Photo courtesy of the School of Optometry.
On April 8, cities in 13 states will experience a total solar eclipse. The path of totality includes Indiana University campuses in Bloomington, Columbus, Kokomo, Indianapolis and Richmond.
Dr. Hin Cheung, a clinical assistant professor at the Indiana University School of Optometry, explains how to prepare to view both eclipses safely.
Question: How can I protect my eyes during the eclipse? How can I safely watch it?
Answer: The best way to protect your eyes is to either view the eclipse indirectly using a pinhole projector, or to view it directly with an eclipse viewer.
For indirect viewing, do not look at the sun, but instead look at a projection of the sun or a shadow of the eclipse. One easy way is to form a waffle pattern with your fingers, with your back toward the sun; the small holes between your fingers form a pinhole effect, and that projects an image of the sun on the ground. As the eclipse occurs, you’ll see the projected image of the sun going from round to a crescent shape.
There are other ways to create a pinhole projector or a sun funnel to view the eclipse indirectly. The American Astronomical Society has more instructions on their website if you’re interested in a “do-it-yourself” project that could be fun for the family.
Direct viewing means you’d look directly at the sun, and the only safe way to do this is through an eclipse viewer. This applies not only during an eclipse; it is NEVER safe to look directly at the sun without proper filters.
Eclipse viewers have special filters that blocks out the harmful levels of light and radiation from the sun and allow only a small fraction of that through the filter — limited solar ultraviolet A and B radiation to a maximum of 0.0032%, and solar infrared radiation to a maximum of 3%. The viewers must be in compliance with the requirements of the International Organization for Standardization to be considered safe. Specifically, there should be clear labeling on the viewer that says ISO 12312-2.
Q: Why shouldn’t you look directly at the sun during the eclipse?
A: Excess UV radiation from the sun can damage the eyes. To the front of the eye, this could cause photokeratitis, which is akin to a sunburn on the cornea. This heals fairly quickly and is simple to treat, but it can be very uncomfortable and cause blurry vision until it is healed.
To the back of the eye, this could cause solar retinopathy, which is damage to the retina. If the eye is like a camera, the retina is like the film. If you damage the film, it’ll damage the photograph. In the same way, if the retina is damaged, our vision can be damaged.
The longer you look at the sun, the more damage will occur. Photochemical damage is cumulative. Starring at the sun for short periods at a time does not protect you; the damage from each viewing adds up. This may cause temporary or even permanent changes to your central vision, which most of us rely heavily on for everyday tasks from driving to watching TV, playing catch to threading a needle.
The changes may be blurry vision, distortions to your vision, changes to your color vision perception or a blind spot to your central vision. The potential lifelong consequences can decrease your quality of life and can be easily avoided by viewing the eclipse indirectly or directly with proper eclipse viewers.
Q: Where can I find safe and legitimate eye protection?
A: You can find safe and legitimate eclipse viewers from your local library or science center. For example, the Monroe County Public Library has a limited number of these viewers that are free to the public. You might have luck by contacting local astronomy clubs as well.
Students, faculty and members of the public gather for a viewing party for the solar eclipse at the Conrad Prebys Amphitheater at Indiana University Bloomington on Monday, Aug. 21, 2017. (Photo by James Brosher/Indiana University)
If you want to purchase your own eclipse viewers, I recommend going to the AAS website to see their endorsed list of vendors.
I would not recommend ordering from Amazon or other online marketplaces not listed as an endorsed vendor by the AAS. There are fake eclipse viewers being sold online that claim they are ISO certified but are not, and therefore can be dangerous for your eyes.
Q: Can I use anything other than eclipse glasses to view the eclipse? Why can’t I use sunglasses?
A: If you happen to have welding filters with a shade number of 12 or higher, these are also safe. AAS recommends a shade level of 13 or 14 for the best comfort, as a shade level of 12 while safe can be uncomfortably bright. These can be difficult to find in supply stores, so unless you already have one, I would not recommend trying to buy one.
Sunglasses, regardless of how dark they appear, or how many pairs of them you wear, will not reach this level of protection and therefore are NOT safe for viewing the sun or the eclipse directly.
Improper eye protection for viewing the eclipse include:
Sunglasses (or multiple pairs of them).
Photo film negatives.
Neutral density filters.
Damaged eclipse viewers.
Q: How long do eclipse glasses last? Can I use them for more than one eclipse?
A: If your eclipse viewers meet the requirements for ISO 12312-2, they will not expire and can be reused as many times as needed, given they are in good condition. Older types of eclipse viewers made prior to ISO 12312-2 standards could be made from materials that degrade over time, which makes them unsafe over time. These viewers may have a warning to discard if more than three years old, or to not view the sun for more than 3 minutes at a time.
A total solar eclipse as seen on Aug. 21, 2017, above Madras, Oregon. Photo courtesy NASA. Photo courtesy NASA/Aubrey Gemignani
If you have a modern eclipse viewer that meets ISO 12312-2 standards, these warnings do not apply. They will not expire and can be reused as many times as needed. With that said, the more you use and handle the eclipse viewer, the more likely it will experience some wear-and-tear damage over time.
ALWAYS check for damage prior to use. This could include scratches and dents to the filters, or if the filter is torn or coming loose from the frame, then do not use this viewer.
If your viewer is damaged, removed the lenses and throw in the trash and recycle the cardboard. If your viewer is in good condition and you want to store it safely, store at room temperature in a case or container that will keep them clean, dry and protected from scratches, dents and punctures. If your viewer is in good condition, but you don’t want to keep it, you can consider donating it to Astronomers Without Borders.
Q: Is there a way to safely photograph an eclipse or use binoculars? Do I need special equipment?
A: The stunning photos of eclipses that we see require special cameras and filters. For the photography or videography enthusiasts and amateurs alike, I would recommend checking the tips for shooting photos from the American Astronomical Society to start.
For the average person using your smart phone, this can work too, but smartphone cameras have a tendency to struggle with overexposure of bright objects or focusing on dim objects. Another factor is that we may not have steady hands to capture a clear and crisp image while holding our phones.
You can consider using a tripod or turning on the high dynamic range (HDR) feature on your phone. If you are pointing your phone camera at the sun for seconds at a time, it is unlikely to damage camera sensor. However, prolonged exposure of intense sunlight can cause heat to build up and damage the camera. Also, it’s important to remember to look at the phone screen and not at the sun directly when taking your photos or videos.
Viewing instruments like binoculars or telescopes must have special filters to safely view the eclipse. Otherwise, it is dangerous to view the sun with these. Binoculars and telescopes can be used as a projection system onto the ground or a uniform background like a sheet of paper. This is the same concept as the pinhole projection, where you look at the projected image of the sun and the shadow of the eclipse, never directly at the sun itself.
Q: What can you do if you can’t find proper eye protection during a partial or total solar eclipse?
A: If you are unable to get an eclipse viewer to look at the sun directly, the only way to safely watch the partial phases of the eclipse is indirectly, as stated earlier. IU Astronomy will also have a livestream if you want to watch online.
You can also look on the ground underneath tree leaves. The gaps between leaves form small pinhole effects; during the partial phases, you will see crescent-shaped lights projected on the ground. This could be a neat way to experience the partial eclipse in October 2023, if it isn’t cloudy.
For the total eclipse in April 2024, there likely won’t be many leaves on the trees for this method to work. However, there’s good news: The only way to view the eclipse directly and safely without eclipse viewers is during the moment of totality.
Totality means that the sun is completely covered by the moon. It is safe to view the totally eclipsed sun without eclipse viewers. When totality occurs, you can take your eclipse viewers off. As totality comes to an end, pay attention! The moment you start to notice any level of sunlight coming through, make sure to put your viewers back on.
Many areas of Indiana will be in the path of totality in April 2024. To check if your city or town will be in the path of totality, and also what time of the day totality will occur and for how long, visit this interactive map.
For example, totality is expected to occur in Bloomington at 3:04:52 p.m. and will last 4 minutes and 2 seconds. For Indianapolis, totality will occur at 3:06:04 PM and will last for 3 minutes and 49 seconds. The closer you are to the center of the path of totality, the longer totality will last.