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Millions of people across Mexico, the United States and Canada will see a spectacular total solar eclipse on April 8.
Astronomers are urging everyone within the path to enjoy this rare sight for the last time until August 2044 – but only if they can do so safely. And sunglasses are not enough to protect your eyes for this heavenly event.
A total solar eclipse occurs when the moon passes between the Earth and the sun, completely blocking the face of the sun.
Those within the path of totality, or locations where the moon’s shadow will completely cover the sun, will see a total solar eclipse. People outside the path of totality will still be able to see a partial solar eclipse, where the moon only blocks part of the sun’s face.
If your location only offers a view of the partial solar eclipse, some of the sun’s powerful light will still be visible. And not only is any view of the brightness of the sun with the naked eye uncomfortable, it is dangerous.
Why you shouldn’t look directly at the eclipse
The only time it’s safe to see the sun without eye protection is during a “total” total solar eclipse, or the brief hours when the moon completely blocks sunlight, according to NASA.
Staring directly at the sun can cause blindness or impaired vision. During the 2017 total solar eclipse, a young woman was diagnosed with solar retinopathy, retinal damage from exposure to solar radiation, in both eyes after viewing the eclipse with what doctors believed were eclipse glasses not held up to safety standards.
There is no treatment for solar retinopathy. It may improve or worsen, but it is a permanent condition.
Use eclipse glasses and solar viewers
To view the eclipse, wear certified eclipse glasses or use a handheld solar viewer. Separately, you can observe the sun with a telescope, binoculars or a camera with a special solar filter on the front, which functions in the same way as eclipse glasses would.
“You need ISO 12312-2 certified eclipse sunglasses. Many vendors are safe online,” said Alex Lockwood, head of strategic content and integration for the Science Mission Directorate at NASA headquarters. “We can’t stress enough how important it is to get a pair of eclipse-safe sunglasses to view this incredible event.”
Sunglasses will not work as a substitute for eclipse glasses or solar viewers, which are 100,000 times darker and held to an international safety standard.
The lenses of the eclipse sunglasses are made of a black polymer, or resin infused with carbon particles, which blocks almost all visible, infrared and ultraviolet light, according to The Planetary Society. Sunglasses do not block infrared radiation.
For safe manufacturers and resellers of eclipse glasses and filters for optical devices, including cameras and smartphones, check the list maintained by the American Astronomical Society.
Put on your eclipse glasses before you look up and remember to look away from the sun before you take them off again. Always keep an eye on any children wearing eclipse glasses to make sure they don’t remove them while looking at the sun.
If you normally wear glasses, keep them on and put eclipse glasses over them or hold a handheld viewer in front of them, according to the American Astronomical Society.
Do not look at the sun through any unfiltered optical device — camera lens, telescope, binoculars — while wearing eclipse glasses or using a handheld solar viewer, according to NASA. Sun rays can still burn through the filter on the glasses or the viewer, given how thick they can be through an optical device, and can cause serious eye damage.
It is also possible to use welded filters to view the eclipse safely because the international safety standard for using such filters to view the sun has been partially removed.
Welding filters made of tempered glass or metal coated polycarbonate and with a shade number of 12 or higher allow for safe viewing, but many find a shade of 13 or 14 to be the best and like wearing eclipse glasses, according to the Association Astronomical America. Just know that the sun will appear green instead of yellowish-orange or white. These filters are usually not on the shelf at supply stores, but may be available online.
Automatic darkening or adjustable welding helmets are not recommended as they may not get dark enough to see the sun.
Keep your glasses
As long as the eclipse glasses or solar viewers you are using meet the ISO 12312-2 safety standard and are not torn, scratched or damaged in any way, they do not “expire” and can be used on for an indefinite period. Also, there is no limit to how long you can look at the sun while wearing them.
Some outdated glasses and viewers carry warnings about using the glasses for more than three minutes at a time or recommend throwing them away after more than three years, but these do not apply to ISO 12312 certified viewers -2, according to the American Astronomical Society. .
Save your eclipse glasses and viewers for future eclipses by storing them at room temperature in an envelope or their original packaging to avoid scratches.
Never use water, glass cleaner, baby wipes or other wet wipes to clean eclipse lenses – the moisture may separate the cardboard frames from the lenses. Instead, carefully wipe the lenses clean with a tissue or cloth.
Indirect observation of the eclipse
If you don’t have certified glasses on hand, an eclipse can be viewed indirectly using a pin projector, like a hole punched through an index card. These work when you stand with your back to the sun and when you stand the card. The pin projects an image of the crescent or ring-shaped sun onto the ground or other surfaces.
But don’t face the sun and look directly at it through the pinhole.
Other pin throwers you may already have are colanders, straw hats or anything with small holes in it. Or you can hold your hands up, space your fingers apart and cross them over each other to create a waffle pattern. The small space between them will show the sun’s crescent during a partial eclipse or a ring during the annular eclipse.
Permanent with a leafy tree? The small spaces between leaves will soften the patterns of the eclipse phase on the ground.
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