How long can you safely look at an eclipse?

NEW YORK, USA - AUGUST 21: A woman observes the total solar eclipse with solar eclipse glasses at the Times Square in New York City, United States on August 21, 2017. (Photo by Volkan Furuncu/Anadolu Agency/Getty Images) (Getty Images)

Eclipse safety isn't just about the right eyewear or a pinhole camera

The solar eclipse of April 8 will be an unforgettable experience (at least, for anyone whose view isn't literally clouded over). But it could also be dangerous for those who don't take proper precautions. 

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Having the right viewing solution is very important, of course – but ensuring that you don't damage your eyes during the event goes beyond your choice of equipment.

Here's what NASA says about how long you can look at an eclipse.

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How long can you safely look at an eclipse?

If you’re wearing eclipse glasses, you’ll still want to look away every few minutes. 

NASA warns that "staring at the Sun for minutes at a time even with proper filters can still overheat the tissues and fluids in the eye." 

That can be dangerous. 

Just like the rest of your body, your eyes must stay at a reasonable temperature to function normally. For example, continued exposure to warmer temperatures can cause quick tear film evaporation, which puts a person at risk for dry eye disease.

And dry eyes can lead to all sorts of other complications.

So even though it’s riveting to watch, you’ll want to glance away often to keep all those important eye fluids at a reasonable temperature.

How can you watch the eclipse safely?

With a brief exception (it’s called totality – more on that below), it is very unsafe to look directly at an eclipse. Luckily, there are several ways to watch the progression of the eclipse before and after totality. Those methods include:

  • Eclipse glasses
  • Pinhole camera (the DIY cereal box method)
  • Colander (yes, really!)
  • Handheld eclipse viewer
  • Welding filter or welder’s glass, shade 13 or 14
  • Solar filters for cameras, telescopes and binoculars

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How can I tell if my eclipse glasses are safe?

Eclipse glasses need to meet the ISO 12312-2 international standard for direct sun viewing, according to the American Astronomical Society. You can also try the following at-home test.

NASA says before you take your eclipse glasses out to the main event, do the following checks to make sure they’re safe to use.

First, find a bright light – like a lamp or flashlight – then hold your eclipse glasses up to the light and look through them. The light should appear extremely dim or not at all. 

"You should only be able to see the filament of a light bulb, but not the glow surrounding the bulb," NASA says. 

If your eclipse glasses have any marks or scratches on them, throw them away. 

If you’re using older glasses from a previous eclipse, make sure they haven’t been damaged or scratched. 

Glasses considered safe for eclipse-viewing will meet the ISO 12312-2 standard, so look for that label, but organizers of the Solar Eclipse Across America website say they’ve found some glasses that say they’re compliant but are not. The website recommends checking out its page of verified safe eclipse viewers and glasses

Why is looking at an eclipse unsafe?

This warning isn’t an old wives tale – sitting too close to your TV won’t make you go blind, but staring directly at an eclipse can do serious damage. 

Even though the sun becomes obscured partially or entirely during an eclipse, what remains visible can cause significant harm to the eyes, potentially leading to permanent vision trouble (blurred vision, dark or yellow spots, pain in bright light, or loss of vision in the center of the eye).

Retinal burn (also called solar retinopathy) happens when sunlight floods the retina. This can overstimulate the cells and cause destruction. What’s more, there’s no warning of the damage, because retinas don’t have pain receptors – so while our fingers warn us when they touch a hot stove, our retinas have no such alarm system. 

This isn’t a danger exclusive to eclipses and other astronomical events (you should never look directly at the sun). But because an eclipse is such a rare and often awe-inspiring occurrence, people are far more likely to risk it, thus exposing themselves to harmful solar radiation. 

Use eclipse glasses or another protective device, whether store-bought or homemade. 

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What time is the solar eclipse?

Southern Texas will see the peak of totality first, around 1:30 p.m. Central Daylight Time. Then Dallas at 1:42 p.m., with the time getting later and later as the moon’s shadow moves north. Indianapolis will see the peak around 3:05 p.m. Eastern Daylight Time; Cleveland at 3:15 p.m., and northern Maine around 3:30 p.m.

However, it will take several hours for the moon to move across the sun, so the actual eclipse event will start just over an hour before the peak of totality, with more and more of the sun slowly being blocked.

How long is the solar eclipse?

Again, that depends on where you are. Those closest to the center of the path will see total darkness for about four minutes at the peak of totality.

But because the moon moves slowly across the sun’s path, the entire eclipse event – from when the moon first clips the sun until the time it clears – will last from 90 minutes to over two hours for those in the path of totality.

Where do I look for the solar eclipse?

The easiest way to know may be to step outside in the days leading up to the eclipse and see where the sun is during the afternoon.

MORE: How to get the best view of the solar eclipse

Early afternoon on April 8, the sun will be pretty high in the sky. As always, though, the further north you are, the lower in the sky the sun will appear.

For example, in Austin, the sun will be at 67 degrees up from the horizon at the peak of totality. Remember, 90 degrees is straight up, so 67 degrees is just over two-thirds up into the sky from the horizon.

In Cleveland, meanwhile, the sun will be slightly lower, at only 49 degrees – just over halfway up in the sky.

When is the next total solar eclipse?

After 2024, NASA says, the next total solar eclipse visible from any point in the contiguous United States will occur in 2044. Totality will only be visible from North Dakota and Montana.

The next total solar eclipse that will travel across the lower 48 states from coast to coast is in 2045. ​

This story was reported from Chicago. The FOX TV Digital team contributed to this report.