A solar eclipse occurs when the moon blocks any part of the sun. On Monday, August 21, 2017, a solar eclipse will be visible across all of North America. The whole continent will experience a partial eclipse lasting 2 to 3 hours. Halfway through the event, anyone within a roughly 70-mile-wide path from Oregon to South Carolina will experience a brief total eclipse, when the moon completely blocks the sun’s bright face for up to 2 minutes 40 seconds, turning day into night and making visible the otherwise hidden solar corona — the sun’s outer atmosphere — one of nature’s most awesome sights. Bright stars and planets will become visible as well.

Looking directly at the sun is unsafe except during the brief total phase of a solar eclipse, when the moon entirely blocks the sun’s bright face, which will happen only within the narrow path of totality .

The only safe way to look directly at the uneclipsed or partially eclipsed sun is through special-purpose solar filters, such as “eclipse glasses” or hand-held solar viewers. Homemade filters or ordinary sunglasses, even very dark ones, are not safe for looking at the sun. To date four manufacturers have certified that their eclipse glasses and handheld solar viewers meet the ISO 12312-2 international standard for such products: Rainbow Symphony, American Paper Optics, Thousand Oaks Optical, and TSE 17.