Eye safety critical during eclipseAug 18, 2017 From nationaleclipse.com
The most important aspect of any solar eclipse is eye safety.
While it's perfectly safe to view a solar eclipse using safe eclipse viewing procedures, incorrect viewing can cause permanent eye damage or even blindness.
Use specialeclipse safety glasses or viewersto view a partial eclipse, an annular eclipse, and the partial phases of a total eclipse.
Although it may be tempting to look directly at an eclipse with unprotected eyes when so much of the sun is obscured, the small amount of light emitted during even a 99.9 percent partial eclipse is still dangerous.
Theonlytime it's safe to look at atotaleclipse without proper eye protection is during the very brief period of "totality" when the sun is 100 percent blocked by the moon.
Make sure that eclipse safety glasses or viewers are certified as meeting international standards for safe solar viewing. The current standard for safe solar viewing is ISO 12312-2; all eclipse safety glasses or viewers should have this designation printed on them.
Take care to purchase glasses or viewers from a reputable seller and be wary of knockoff products that claim to be safe but aren't.
Be very careful and don't use any product unless claims of safety can be verified.
NASA is reportingthat unsafe eclipse glasses are being distributed. To tell what is safe, look for the manufactuere's name and the "ISO" icon. The glasses must have ISO reference 12312-2. If lenses have scratches, don't use them. If lenses are wrinkled, they're not safe for viewing the eclipse. If they're older than three years, they're not recommended. Read all of the safety instructions that came with them.
Children should always be supervised by a responsible adult when using eclipse safety glasses or viewers.
Unless a product has been specifically designed for safe solar viewing and has been certified as meeting international standards for such products, it's best to assume that a device, method, or instrument is unsafe. Items such as regular or polarized sunglasses, smoked glass, exposed film, medical x-rays, homemade filters, and many others are all unsafe.
Welder's glass may be used to view an eclipse, but it must be No. 14 welder's glass; any rating below No. 14 is not safe.
It's also safe to view an eclipse using indirect methods, such as projecting an image of the eclipsed sun onto a white screen. Search online for "pinhole projector" and follow the instructions provided by a trusted organization like NASA.
When to wear glasses
In the narrow path of totality, don't remove eclipse glasses until the very last bit of the sun is gone.
Again, it's only safe to look with unprotected eyes when the sun is 100 percent blocked by the moon and only the soft wisps of the solar corona are visible.
Once totality begins, it's important to knowpreciselywhen totality will be ending. Put on eclipse glasses before the first brightness of the exposed sun is revealed.
The definitive source to determine the exact start time, end time, and duration of totality for any location is NASA's interactive Google map of the eclipse.
Allow for a very generous margin of error.
Additionally, NASA advises paying careful attention to the edge of the moon opposite of where the sun last appeared. When a very slight crescent-shaped brightening is visible, totality is coming to an end. Look away or put eclipse glasses back on before the first flash of exposed sunlight.
Note that attempting to view an eclipse using cameras, binoculars, telescopes, or other optical devices without proper solar filters is extremely hazardous and can permanently damage the eyes in an instant. These devices need specially designed solar filters that fit snugly on the front end (the sun side) of the device.
Neverattempt to view an eclipse through an optical device using eclipse glasses or any type of filter that attaches to the viewing side (as opposed to the sun side) of the instrument; the focused light will destroy the filter and enter and damage the eyes.
Since viewing or photographing a solar eclipse with an optical device requires specialized equipment and knowledge, consult with a qualified astronomer or just enjoying the eclipse using safe eclipse viewing procedures.