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Ask the Expert: Protecting your eyes during a solar eclipse

Oct 11, 2023

EDITOR’S NOTE: This October 2023 story was updated on March 19, 2024, to focus on safety for the April 8 total solar eclipse.

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, assistant clinical professor at the Indiana University School of Optometry. Dr. Hin Cheung, assistant clinical professor at the Indiana University School of Optometry.

Dr. Hin Cheung, a clinical assistant professor at the Indiana University School of Optometry, explains how to prepare to view the total solar eclipse safely. For additional downloadable and sharable resources, visit the eclipse resource webpage from the IU School of Optometry.

Question: How can I protect my eyes during the eclipse? How can I safely watch it?

Answer: The best way to protect your eyes in the hours leading up to and after the moments of totality during the total solar eclipse is to either view the eclipse indirectly using a pinhole projector, or to view it directly with a reputable eclipse viewer. When the sun is completely covered by the moon during totality, it is safe to remove eye protection and enjoy the view of the totally eclipsed sun directly.

For indirect viewing during partial phases of the eclipse, instead of looking at the sun, 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 partial 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.

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, sometimes written as ISO 12312-2:2015.

If you wear glasses, simply wear the eclipse glasses or hold the handheld solar viewer over your glasses. Cover your eyes with the solar filter before looking at the sun, and turn away from the sun before removing the solar viewer. Do not remove them while looking at the sun.

Eclipse viewers are not meant to be used in combination with unfiltered cameras, telescopes or binoculars. These optical devices focus light, and the concentrated sunlight can burn through the filter and damage your eyes.

Filtered cameras, telescopes and binoculars specifically designed for sun viewing are safe to use. Specially designed filters can also be purchased and fit over an unfiltered camera, telescope or binoculars to make it safe for sun viewing. The AAS has further recommendations.

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. IU Astronomy will also have a livestream if you want to watch it online.

Question: What is totality?

Answer: Totality means that the sun is completely covered by the moon. It is safe to view the totally eclipsed sun without eclipse viewers. 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.

A total solar eclipse as seen on Aug. 21, 2017, above Madras, Oregon. Photo courtesy NASA. Photo courtesy of NASA/Aubrey Gemign... A total solar eclipse as seen on Aug. 21, 2017, above Madras, Oregon. Photo courtesy NASA. Photo courtesy of NASA/Aubrey Gemignani

Many areas of Indiana will be in the path of totality on April 8. 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 will 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 p.m. and last for 3 minutes and 49 seconds. The closer you are to the center of the path of totality, the longer totality will last.

If you will be viewing the eclipse in Bloomington, here are the times you need to know:

  • 1:49:11 p.m.: Partial phase of the eclipse begins; use eclipse viewers.
  • 3:04:52 p.m.: Total phase of the eclipse begins; it is safe to remove eclipse viewers during totality.
  • 3:08:54 p.m.: Total phase of the eclipse ends; time to put eclipse viewers back on!
  • 4:22:29 p.m.: Partial phase of the eclipse ends; use eclipse viewers for this phase.

Q: Why shouldn’t you look directly at the sun during the partial phases of the solar 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. Don’t risk the health of your eyes! If you’re lucky, you get two good ones in a lifetime.

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 will have a limited number of these viewers; these will be in stock on March 11. 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... 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

Our IU Department of Astronomy will open the Kirkwood Observatory from noon to 3 p.m. Saturday, March 23, and solar viewers will be available at the time. If you are a patient at the Atwater Eye Care Center, you can also stop by to claim a viewer.

IU Science Fest will also have free eclipse viewers, and the public will have an opportunity to learn about the science of eclipses. Hosted by the College of Arts and Sciences, this family-friendly event takes place from 9 a.m. to 3 p.m. Saturday, April 6, on the Bloomington campus.

Eclipse glasses will also be available at other places on IU’s campuses. If you want to purchase your own eclipse viewers, I recommend going to the AAS website to see their endorsed list of vendors. You can also check out this video from NASA that shows you how to tell whether your eclipse glasses are safe.

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 partial 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, will not reach the level of safety to protect your eyes and therefore are NOT safe for viewing the sun or the partial eclipse directly. Eclipse viewers are at least 1,000 times darker than the darkest sunglasses!

Improper eye protection for viewing the eclipse include:

  • Sunglasses (or multiple pairs of them).
  • Smoked glass.
  • Photo film negatives.
  • X-ray film.
  • Polarizing filters.
  • 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 (which was adopted in 2015), 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 outdated 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.

Unfortunately, some manufacturers have continued to print these outdated warnings on new ISO 12312-2 eclipse viewers, which adds to the confusion. Per the AAS, if you have a modern eclipse viewer that truly meets ISO 12312-2 standards, these warnings do not apply. If you saved your eclipse viewers from the 2017 eclipse and they are still in good condition, you may reuse these again. With that said, always check for damage prior to using the viewer, the more you use and handle the eclipse viewer, the more likely it will experience some wear-and-tear damage over time. While the 3-minute rule does not apply to the new ISO 12312-2 eclipse viewers, there really is no reason to constantly stare at the sun. The eclipse occurs very slowly and there is no need to look more than a few seconds every few minutes during the partial phases until totality.

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.

Question: Which side of the solar viewer/filter do I look through?

Answer: While it is safe to look through either side of the filter to view the eclipse, there is technically a front and back to the filter. If you look closely at the surface of the filter, one side will be more shiny or reflective, while the other side will be duller.

The duller side will also have the printed directions, and that is the preferred side to face your eyes. The shinier, more reflective side will usually have printed designs and logos, and that should face the sun.

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.

NASA also has some tips and recommendations for smart phones. There are also free solar eclipse apps for iPhone and Android smartphones. Two examples are Totality, sponsored by the AAS, and Solar Snap, available on the Great American Eclipse website.

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.


IU Newsroom

Teresa Mackin

Deputy Director of Media Relations, Indianapolis

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