There’s a good chance that more people on Earth will witness the August 21 total solar eclipse than any other eclipse in history. Many will share in the sight thanks to a flood of eclipse glasses available free or through a myriad of online outlets. But as in any endeavor to lift people up, there’s always a fringe element working hard to figure out ways to cheat the system and profit. The latest scam is fake eclipse glasses. These are eclipse shades that aren’t up to specs and allow dangerous visible, infrared and ultraviolet light into your eyes, where it can damage your retinas.
You used to be able to look for the logo of the International Organization for Standardization (ISO) on filters indicating that it meets the ISO 12312-2 international safety standard for filter for direct viewing of the sun. Even that may not safe anymore because certain outfits are printing that on the product even when it doesn’t meet the standard. Fortunately, there are a couple sure fire ways you can verify you have safe eclipse glasses or hand-held filters.
Libraries across the U.S. will be handing out 2 million pairs of free eclipse glasses. Those plus any glasses from a planetarium, science museum or astronomy trade show comply with standards and are safe. Major suppliers such as Rainbow Symphony, Thousand Oaks, B&H Photo, Walmart, 7-Eleven and MANY others are perfectly fine. Just be careful going online and grabbing a pair from someone NOT on the American Astronomical Society’s (AAS) list of Reputable Vendors of Solar & Viewers.
To be fair, just because a business isn’t listed doesn’t necessarily mean their filters are unsafe, simply that the AAS has no knowledge of them and can’t vouch for that outlet meeting standards. Remember that you can also buy a safe #14 welding glass filter from a welding supply company, but make sure it’s a #14. Don’t get a #13 if they’re out of #14s!
You can also check your filter to be sure it’s doing its job. A compliant solar filter will show the sun surrounded by a dark sky. It will also show the interior or filament of a bright light bulb or LED if you get right on top of it. (I’ve tried this with my own safe filters). You shouldn’t be able to just look through a filter and see ordinary household lights. If you do, send it back for a refund.
So what does happen if you stare at the sun? Will you go blind? We have a built-in aversion to looking directly at the sun. I can’t even imagine doing it. Direct sunlight overloads the retina with light, causing it to release chemicals that can damage it. Unlike grabbing a hot pot bare-handed, where you instantly feel the back and withdraw, most of us don’t sense pain in our retinas, making looking at the sun even more dangerous.
Medical journals record instances of retinal damage via sunlight called solar retinopathy. For some, vision returns to normal after several months. Others see a ghostly crescent (from the crescent sun) floating in their vision for years. English astronomer Thomas Harriot, who studied sunspots in 1610, reported that his “sight was dim for an houre” after solar observations. Isaac Newton nearly lost his vision for three days after trying to provoke afterimages, those dark shapes you see when someone pops a camera flash in your eyes, by staring at the sun in a mirror. He got afterimages alright … for months! Newton’s vision eventually recovered.
A final note. You’ll need a filter if you’re observing the sun at any time other than when it’s totality eclipsed by the moon. That’s easy to remember. During totality you can remove it and take in the spectacle.
You can also view the sun indirectly under a leafy tree — the tiny gaps between the leaves act as pinhole lens projectors and will beam a blizzard of tiny solar crescents on the ground below. Or you can project a crescent sun through the little hole in your almost-clenched fist onto a piece of paper.
There are lots of safe ways to enjoy an eclipse.