Argh, my eyes! or why don't we look at an eclipse.
March 19, 2009 9:08 PM   Subscribe

BlindedByTheLightFilter: You aren't supposed to look at an eclipse directly because you can damage your eyes without knowing it. Is that because you aren't supposed to look at the sun directly ever, though you might be tempted to do so by an eclipse; or is there something especially insidious about the effect of looking at an eclipse on one's eyes?

Side note: as a child, I was a bit of a hypochondriac, and, when there was an eclipse - even a partial one - I would be terrified of going outside for fear that I would accidentally see the eclipse and my eyes would explode. I am no longer afraid of this, but still curious about the warnings.
posted by blahblahblah to Science & Nature (8 answers total) 4 users marked this as a favorite
The problem with an eclipse is that the ambient light is low, so your pupil is dialated. Then if you look at the sun, such as it is, you get too much light entering your open pupil. Only it's sunlight, not a light bulb, and full of the usual UV rays. I will give you, they make it sound like a horror. Back in the early 60's, when I was quite young, I was made to stay indoors (in our basement, with a good portion of the rest of the neighborhood kids) during the eclipse that happened then. I didn't even grasp exactly what was happening, else I'd have thrown a fit (and friend my eyes?).
posted by Goofyy at 9:16 PM on March 19, 2009 [1 favorite]

I was always told that eclipses were particularly dangerous only in that they seemed dim enough to be looked at directly, while in fact the eclipse was much brighter than the retina is able to handle.
posted by tjenks at 9:17 PM on March 19, 2009

Much of the visible light of the sun is obscured by the moon, so your iris opens more, allowing the invisible but extremely damaging ultraviolet rays from the sun's corona to penetrate your retina.
posted by weapons-grade pandemonium at 9:21 PM on March 19, 2009

People give that warning because an eclipse is an interesting thing, so people might be tempted to look directly at the sun. Viewing the sun doesn't burn your retina with heat, but the short wavelengths can cause photochemical problems (like blindness). So during the eclipse, you think it's not as bright but the UV rays still affect your retina. When there isn't an eclipse, your natural photophobia in extreme lighting conditions kicks in.

This page has some interesting information on it about sun damage to retinas.
posted by demiurge at 9:33 PM on March 19, 2009

Insidious, yes. It's comparable to wearing dark sunglasses that aren't UV proof, so your eyes say, "Oh, no problem here," when there is, in fact, a very serious problem. Evolution didn't bother with eclipse scenarios.
posted by weapons-grade pandemonium at 9:37 PM on March 19, 2009

I would put this with this story... Father says "Don't watch me arc-weld, it will burn your eyes out.", me... I watch, it doesn't hurt... that night I'm screaming in pain, end up in the Emergency Room and wearing patches over both of my eyes for 2 weeks. Damn lucky I'm not blind. That UV that you may be looking directly at may not hurt at the moment, but it will fry your eyes within a few minutes. Usually the brightness of the sun makes you turn away quickly, during an eclipse it seems sort of dark and you can take a longer peek. That longer peek will burn your eyes out like watching arc-welders.
posted by zengargoyle at 2:41 AM on March 20, 2009 [1 favorite]

Yikes, I'm glad you're okay, Zengargoyle.

I have "eclipse glasses" that I got free at the Museum of Science years ago, and kept. They're easy to acquire, and might set your mind at ease.
posted by theora55 at 7:47 AM on March 20, 2009

Back in 1994, there was an annular eclipse visible in Ohio where I went to college. I was a physics student working in an optics lab, so my co-workers and I grabbed some neutral density filters of appropriate attenuation and went out to see the fun.

When I got back to my dorm, my boyfriend was bursting with news that he had figured out a much easier way to view the spectacle -- through a compact disk. And he had told everyone else at the dorm...

I was aghast. I had no idea what the UV and IR transmissivities of the aluminum film in a CD were. (Solar UV or IR will happily fry your rods and cones or denature proteins in your lenses.) Was the entire population of my dorm about to go blind? Or get cataracts? Now or in 20 years?

So today, with the wonder that is the web, I know the answer: maybe.
    I have recently also found a wide range of optical density between individual audio and data compact disks (CD and CD-ROM) because of variations in manufacturing processes. Some compact disks have aluminum films which are so thin that they appear semi-transparent at normal room illumination levels. These CDs are unsuitable for use as solar filters. Higher quality CDs are suitable for use if the aluminum coating is dense enough that the glowing filament of an incandescent light bulb is just barely visible through it.
For the record, my boyfriend (now my husband) is okay.
posted by pointless_incessant_barking at 11:34 AM on March 20, 2009

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