People in the continental United States will witness a partial or total solar eclipse next month, but you’ll need to take precautions to avoid damaging your eyes.
On April 8, the Moon will pass between the Earth and the Sun, temporarily blocking the Sun’s light. During the celestial alignment, the afternoon sky will briefly darken along a path more than 100 miles wide that cuts across Mexico, part of the United States, and a small portion of eastern Canada.
Those outside this so-called path of totality will be able to see a partial solar eclipse, in which the moon obscures only part of the sun.
You can wear special glasses or create a pinhole projector to watch the show safely. However, unless they are equipped with a special filter, do not try to view the eclipse with regular sunglasses or use tools such as a telescope, even if you are wearing suitable glasses.
Here’s what you need to know.
How to find suitable eclipse glasses?
Glasses made specifically for looking at the sun offer the only safe way to view the eclipse directly.
D., a comprehensive ophthalmologist at Cleveland Clinic Cole. “Eclipse glasses are very important to prevent photothermal damage to the retina, and not just for old glasses; they need to be eclipse glasses with ISO 12312-2 filters,” said Nicole Bajic. Eye Institute.
The glasses are “thousands of times darker” than sunglasses, according to NASA.
Watching the eclipse without taking such precautions can cause permanent eye damage.
“This is called solar retinopathy, and it is damage to the very delicate, complex cells that make up the retina, which covers the back of the eye, and is what transmits light into electrical signals so that we can see what we see.” Bajic said: “And when we damage this tissue from the sun, we can experience decreased vision and central blind spots.”
When and how should you wear your glasses?
The only safe moment to view the eclipse with the naked eye is “the moment when the moon completely obscures the sun’s bright face—during the brief, spectacular period known as totality,” according to NASA, which adds: “You’ll know it’s safe.” when you can no longer see any part of the sun through eclipse glasses or a solar viewer.
Chris Hartenstine, public engagement leader for NASA’s Glenn Research Center in Cleveland, Ohio, said it will become clear when completeness arrives.
“When you put on eclipse glasses and look at the sun, you’ll see the sun’s glare at the edge of the disk, even in the slightest sliver,” he said. “Once that’s completely gone, give yourself a few more seconds and then you can take them off.”
According to NASA, completeness will take approximately three and a half to four minutes, depending on location.
Those who watch the partial eclipse must wear special eclipse glasses throughout the solar eclipse.
For those who want to use tools such as binoculars and cameras, glasses are not enough.
“Viewing any part of the bright sun through a camera lens, binoculars, or telescope without a special-purpose solar filter fixed to the front of the optics will cause immediate serious eye injury,” warns NASA.
How can you make sure your glasses are safe?
NASA does not endorse any particular brand of sunglasses, but points to the American Astronomical Society’s list of safe options and recommends staying away from online marketplaces where third-party sellers may sell counterfeit or poorly processed products. The association warned last week that counterfeit and counterfeit glasses were “polluting the market”.
“The reduction of hands that have to be moved between the time they are produced and the time you receive them will help increase your chances of not receiving some kind of bad or less-than-desirable product,” Hartenstine said. .
If you were one of the millions of people who watched 2017’s solar eclipse and kept a pair, repurposing eclipse viewing glasses is also an option.
“Filters, real lenses, are forever good,” Hartenstine said, but added that you need to make sure the lenses are not damaged, including scratches, punctures or creases.
“If you’re not sure, by all means buy a new pair. But expiration dates are not relevant to ISO standard sun filter material, just because they are printed on the glasses,” said Hartenstine.
How to make and use a pinhole projector
If you cannot find suitable glasses, you can enjoy being eclipsed without looking directly by making a pinhole projector.
The device works by letting sunlight in through a small hole, focusing it, and reflecting it onto a piece of paper, wall, or other surface, creating an image of the sun that is safe to look at.
To make a projector, cut a 1 to 2 inch square or rectangle from the center of a piece of plain white paper or white cardboard. Tape a piece of aluminum foil over the cut out shape, then poke a small hole in the foil using a pin or pushpin. Use a second piece of white paper or cardboard as the screen on which the projected image will appear.
To use your projector, place the paper screen on the floor, stand with the sun behind you, and hold your device with the foil facing up. Be sure to only watch the projected image of the eclipse rather than looking at the sun. Adjusting how far you hold the projector from the screen will change the size of the resulting image.
A colander or other household item with small holes in it can be used in the same way, and sturdier projectors can be made from cereal boxes.
Even simpler: Find a shady tree and look at the ground underneath; You’ll probably see crescent-shaped shadows.
This article first appeared on NBCNews.com.