Some people think there is a myth that staring at the Sun can make you go blind It isn't. If you look at the Sun for too long, it'll do all kind of damage to your eye-balls. Sir Isaac Newton, legendary smart guy, learned that the hard way. He actually would wait in a dark room, so his pupils were dilated, then used one eye to look at a reflection of the Sun in a mirror just to see if it would create some kind of cool after image in his vision when he looked away. Apparently he ended up seeing some lovely circles and colors so he repeated the experiment two more times and then so called "Phantasm" of lights and colors stayed in his vision for months. His eyes did eventually go back to normal but he ended up with sunlight phobia. Good move, Newton.

But he wasn't the only one who ended up with vision problems because of the Sun. Giovanni Cassini, the 17th century astronomer who studied the Saturn, also complained of vision problems from observing the sun early in his career. Galileo must have experienced something similar because he took to studying the Sun by shining the light through a pinhole onto another surface. And that is still one of the safest, simplest ways to observe the Sun.

Sunlight is mostly dangerous because of all of the ultraviolet radiation it has and just a bit of that UV light can hurt your eyes. For example, it can give you photokeratitis, which is basically a sunburn on your cornea, the outermost layer of your eye. It causes blisters, pain and inflammation... Nothing that you want happening to your eyeballs.

Luckily, like regular sunburns, it's usually temporary unless you get a really bad one. Unfortunately, the damage doesn't stop at the top layer. Unlike your skin, your cornea is transparent and allows some of UV light, called UVA radiation to pass into other part your eye and it can damage each of them in different ways. After passing through your cornea, UVA light hits the lens which bends and focuses light. Over time, repeated UV damages to the lens can cause cataracts, invasive tissue growth that makes your vision cloudy, and eventually blindness.

Once it goes though your lens, which is also transparent, the UV light hits your retina, the structure at the back of your eye that transmits images to your brain. Normally light stimulates the retina, which is basically a cluster of sensitive cells, to release signaling chemicals. So when those cells are overstimulated, like if you're looking directly at the Sun, they put out way too much of the stuff. The signaling chemicals can actually damage the surrounding tissues resulting in blurry, dark or even lost vision and that can be permanent. It's called solar retinopathy and it's probably what Newton got. After a while UV light also tends to permanently damage a smaller part, right in the middle of the retina called the macula. Along with some other things, it's responsible for the detail you can see right in the center of your field of vision.

When bright light makes the pupil's contract, any light that still enters the eye hits the macula. Over time that can lead to macular degeneration which causes blind spots in the center of the field of vision. Like cataracts, macular degenerations can come from UV damage over time since we live in a world lit by the sun, the most you can really do is to wear a UV rated sunglasses and avoid looking anything to bright. But also in general just never look directly at the Sun. Not through sunglasses, not through camera filters, and especially not through telescopes, binoculars or other magnifying devices. Those things will concentrate the Sun's light then burn your eyes, which makes a lot of sense if you've ever seen someone focused sunlight through magnifying glass to start a fire. Even looking at the Sun's reflection can be bad. Some materials, like water, glass, snow and sand can be such efficient reflectors, the UV light bouncing off them will still damage your eyes.

It's usually ok though to moon-gaze and it's basically just lit up rock. Instead of being reflected, the most of the light that hits the moon is getting absorbed. But you don't wanna look at the moon when it's in front of the Sun during the solar eclipse. In normal sunlight, your pupils contracting your eyes make little random movements to protect themselves. But during an eclipse, most of the sun's light is blocked, tricking your eyes into thinking that they don't have to do those things. Meanwhile, the part of the Sun that's not blocked is still emitting UV light and your eyes are extra vulnerable. It doesn't mean that you can never see the Sun though. You just have to protect yourself first.

Some people use welding goggles or solar filters, lenses, covered with the thin layer of chromium alloy or aluminum which blocks the most of light. But even this can fail. Welding goggles aren't designed for sun-gazing and solar filters can get damaged. The safest way to look at the Sun is probably still that 16th century pinhole projector. Oh Galileo. Four centuries later and his ideas are still helping us out.

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