by People across the continent will experience a partial or total solar eclipse next month, but you’ll need to take precautions to avoid injury.
On April 8, the moon will pass between Earth and the sun, temporarily blocking sunlight. During the celestial alignment, evening skies will darken for a short period along a path more than 100 miles wide, which cuts across Mexico, part of the US and a small part of eastern Canada.
Those outside the so-called path of totality will be able to see a partial solar eclipse, with the moon obscuring only part of the sun.
To view the show safely, you can wear specialized glasses or build a pin projector. But don’t try to view the eclipse through regular sunglasses or use tools like a telescope to view it – even when wearing the right glasses – unless they’re equipped with a special filter.
Here’s what you know.
How to find the right eclipse glasses
Glasses made specifically for viewing the sun are the only safe way to view the eclipse directly.
“Eclipse glasses are very important to prevent photothermal injury to the retina, and not just any old glasses – they have to be eclipse glasses with the ISO 12312-2 filter,” said Dr. Nicole Bajic, a comprehensive ophthalmologist at the Cleveland Clinic Cole. Eye Institute.
The glasses are “thousands of times darker” than sunglasses, according to NASA.
Without such precautions, viewing the eclipse can cause permanent eye damage.
“It’s called solar retinopathy, and it damages the very delicate, complex cells that make up the retina, which is the lining at the back of the eye, and that’s what transmits light into electrical signals so we can see what that we see,” said Bajic. “And when the sun damages that tissue, we can get reduced vision and central blind spots in our vision.”
When and how to wear your glasses
The only safe moment to view the eclipse with the naked eye is “when the moon completely hides the bright face of the sun – during the brief and spectacular period called totality,” according to NASA, says : “You’ll know it’s safe when you can’t see any part of the sun through eclipse glasses or a solar viewer.”
Chris Hartensine, head of public engagement for NASA’s Glenn Research Center in Cleveland, Ohio, said it will be clear when the total has arrived.
“When you’re wearing the eclipse glasses and you’re looking up at the sun, you’ll see, even the tiniest sliver, of sunlight on the edge of the disk,” he said. “Once that’s completely out, give yourself a few more seconds and then you can take them off.”
The total will last about three and a half to four minutes, depending on the location, according to NASA.
Those viewing the partial eclipse must keep their special eclipse glasses on around the world.
And the glasses are not enough for people who want to use tools like binoculars or cameras.
“Viewing any part of the bright sun through a camera lens, binoculars, or telescope without a special purpose solar filter secured over the front of the optics will cause immediate eye damage,” NASA advises.
How to make sure your glasses are safe
NASA does not endorse any particular brand of solar viewer, but points to the American Astronomical Society’s list of safe options and recommends avoiding online marketplaces where third-party sellers may be selling counterfeit or poorly handled products. The association warned last week that fake and counterfeit glasses are “polluting the market.”
“Having fewer hands to trade parts between the time they’re produced and the time they’re in your hands would help increase your chances that you didn’t get some kind of poor or sub-par product desirable,” Hartensine said. .
Reusing eclipse viewing glasses is also an option if you were one of the millions who caught the 2017 solar eclipse and kept your pair.
“The filters, the lenses are actually good indefinitely,” Hartenstin said, though he said you should make sure the lenses haven’t been damaged, including scratches, punctures or crinkling.
“If you’re not sure, get a new pair of course. But the expiration dates, just because they’re printed on the glasses, don’t apply to ISO standard solar filter material,” Hartensine said.
How to make and use a pinhole projector
If you can’t find proper glasses, you can enjoy the eclipse without looking at it directly by making a pin projector.
The device works by letting sunlight in through a small hole, focusing it and projecting it onto a piece of paper, wall or other surface to create 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 that cut shape, then use a pin or thumb to poke a small hole in the foil. 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 ground, stand with the sun behind you, and hold your device with the foil facing up. Make sure you only see the projected image of the eclipse, rather than looking at the sun. Adjusting how far you hold the projector from the screen will resize the image as a result.
A colander or other household item with small holes in it can be used in the same way, and tougher projectors can be made from cereal boxes.
Even simpler: Find a shady tree and look at the ground beneath it – you’ll probably see crescent shadows.
This article was originally published on NBCNews.com
