The first total solar eclipse in the continental US since 1979 is fast approaching and Amazon sellers are ready. Many who typically sell fad items are hawking solar eclipse glasses—meant to block 99.99% of sunlight, per the Verge—in the lead-up to Aug. 21, taking over a market previously dominated by NASA-approved manufacturers. There are "literally thousands" of glasses up for grabs on Amazon, writes Elijah Wolfson at Quartz. The problem is that they might not do their job. Wolfson and colleagues reviewed 140 of the top listings for "eclipse glasses" on Amazon and found that few met NASA guidelines, which state that the glasses should be unblemished and less than three years old, and include the maker's information and an ISO 12312-2 certification.
Only 33 identified the maker's name, and only 16 claimed to use lenses manufactured by a NASA-approved company. Even those weren't necessarily safe, as Wolfson discovered one such pair he bought was actually counterfeit. Most glasses claimed to be certified, though an official at the American Astronomical Society says he's reviewed plenty that didn’t have complete ISO paperwork. In a series of tests, experts found glasses that didn't meet NASA guidelines did block harmful rays, but that doesn't mean all will. Amazon updated its policy Thursday so sellers must provide proof of ISO certification, but Quartz notes it's not clear if existing listings will be taken down. More from Quartz here, while NASA's tips for buying authentic glasses are here. (Read more solar eclipse stories.)