NASA has issued a warning against unsafe solar glasses and has given guidelines for finding a safe pair ahead of the August 21, 2017 solar eclipse that will be visible across North America.
The space agency recommends glasses from U.S. manufacturers American Paper Optics, Rainbow Symphony, Thousand Oaks Optical or TSE 17. The glasses must have the "ISO" icon with a designation of ISO 12312-2.
It is also recommended not to use glasses that are older than 3 years, or lenses that have scratches or are wrinkled.
On August 21, all of continental U.S. will experience a partial eclipse for about 2-3 hours. A total eclipse will occur coast to coast within a roughly 70-mile-wide path from Oregon to South Carolina. The total eclipse will block the sun's face for up to 2 minutes and 40 seconds, turning day into night.
Special-purpose solar filters or glasses are necessary when looking directly at a partial eclipse. The only time a solar filter is not required is when a total eclipse occurs. A pinhole projector can also be used to safely view a partial eclipse.