On Aug. 21, 2017, the United States will fall dark during the middle of the day.

The Great American Eclipse will begin in Oregon at about 10:15 a.m. PDT and will end about 100 minutes later in South Carolina, around 2:45 p.m. EDT.

“Seeing stars in the daytime…”

According to Astronomy magazine senior editor Michael Bakich, “Everyone in the continental U.S. will see at least a partial eclipse. In fact, if you have clear skies on eclipse day, the Moon will cover at least 48 percent of the Sun’s surface.”

While virtually everyone will experience some of the effects of the eclipse, it won’t be the same for everyone.

“I know that 48 percent sounds like a lot,” writes the Astronomy editor. “It isn’t. You won’t even notice your surroundings getting dark. And it doesn’t matter whether the partial eclipse above your location is 48, 58, or 98 percent. Only totality reveals the true celestial spectacle: the diamond ring, the Sun’s glorious corona, strange colors in our sky, and seeing stars in the daytime.”

The “Path of Totality,” the line of places where the moon will completely shadow the sun, passes through 12 states. People who find themselves within the path will have roughly two minutes, give or take about a minute, to absorb this unique astronomical event.

However, there are risks to observing the eclipse.

Real Danger

“The danger is real for permanent vision loss,” Dr. Russell N. Van Gelder of the University of Washington School of Medicine told Today.

Dr. Van Gelder and other ophthalmologists are worried that people won’t take this danger seriously.

“It’s a big deal for us,” said the clinical spokesman for the American Academy of Ophthalmology. “We don’t have a lot of public health issues in ophthalmology where we’re really worried about things that threaten the eye health of the population […] But this is an event that really hundreds of millions of people are going to be exposed to.”

While people intuitively know not to look at bright lights, Dr. Van Gelder worries that poor planning and a lack of self-control may injure many curious citizens.

“The worry in the eclipse is that people are so interested to see one of the great astronomic spectacles that they will suppress their inner drive to look away from the very bright light,” Van Gelder said.

Even looking at a tiny sliver of the sun in the moments before or after totality can have damaging effects.

Protect Yourself

“Cardboard eclipse glasses with lenses of optical Mylar cost about $2,” explained Astronomy’s Bakich. “Such a device—it’s not a toy—will let you safely look directly at the Sun. It filters out most of the light, all of the dangerous infrared (heat) and ultraviolet radiation, which tans our skin.”

“Another safe solar filter is a #14 welder’s glass, which also will cost you $2,” adds Bakich. “Wanna look cool at the eclipse? Buy goggles that will hold the welder’s glass. I’ve even seen people wearing whole helmets. Either those or goggles serves one purpose—you won’t need to hold the filter, so you can’t drop it.”

NASA has a handful of specific safety tips:

Always supervise children using solar filters.

Stand still and cover your eyes with your eclipse glasses or solar viewer before looking up at the bright sun. After looking at the sun, turn away and remove your filter—do not remove it while looking at the sun.

Do not look at the sun through a camera, a telescope, binoculars, or any other optical device while using your eclipse glasses or hand-held solar viewer—the concentrated solar rays will damage the filter and enter your eye(s), causing serious injury.

Seek expert advice from an astronomer before using a solar filter with a camera, a telescope, binoculars, or any other optical device. Note that solar filters must be attached to the front of any telescope, binoculars, camera lens, or other optics.

If you are within the path of totality, remove your solar filter only when the moon completely covers the sun’s bright face and it suddenly gets quite dark. Experience totality, then, as soon as the bright sun begins to reappear, replace your solar viewer to look at the remaining partial phases.

Outside the path of totality, you must always use a safe solar filter to view the sun directly.

If you normally wear eyeglasses, keep them on. Put your eclipse glasses on over them, or hold your handheld viewer in front of them.

In a Pinch and Final Tips

If you’ve forgotten a filter, explains Bakich, you can still watch by making a pinhole camera. “It can be as simple as two pieces of paper with a tiny hole in one of them,” he writes. “Try to make the hole as round as you can, perhaps with a pin or a sharp pencil. Line up the two pieces with the Sun so the one with the hole is closest to it. The pinhole will produce a tiny image, which you’ll want to have land on the other piece of paper. Moving the two pieces farther apart will enlarge the Sun’s image but will also lessen its brightness. Work out a good compromise.”

If you’re observing the eclipse near trees, look to the ground as well, and you’ll notice the leaves acting as a natural pinhole camera, projecting crescents among the shadows on the ground.

In addition to peeking at the ground as the eclipse approaches, Bakich suggests that during totality, “take just a few seconds to tear your eyes away from the sky and scan the horizon. You’ll see sunset colors all around you because, in effect, those locations are where sunset (or sunrise) are happening.”

The eclipse viewing experience will last two to three hours, but the total eclipse will last less than three minutes. Don’t waste your time trying to capture the perfect picture or doing something silly; be quiet, still, and in the moment so that you can remember this spectacular solar event.