And because part of the sun is obscured, the TOTAL brightness is decreased, which may fool people into thinking it’s less dangerous. But it’s equally dangerous, it just burns a crescent-shaped area of your retina rather than a circle.
Furthermore, during an eclipse there is less light in the spectrum that governs how your irises dilate, so they open up more than they should, letting in invisible spectrum that is (for reasons I don’t recall) much “brighter” during an eclipse and also damaging to retinal tissues. Also, it’s normally very uncomfortable to look at the sun, but it’s not during an eclipse, so people are more likely to look for a long time without discomfort. Alas, the damage doesn’t hurt.
I can’t manage to google up a cite for this, but I did find this page with lots of interesting related information, if you’re bored:
I don’t believe this is true. It’s not instantaneous (it takes seconds or minutes), and the damage can be temporary or permanent. See my link above.
This is very dangerous for the reasons others have mentioned. Exposed film may be opaque in the visible range, but is nearly transparent in the infrared range. When you look through it, your pupils dilate but much of the sun’s energy still reaches your eyeballs. In fact, you can use exposed film (not looking directly at the sun) to view the world in infrared–your eyes can perceive just enough of near-infrared light so that you can see it if you block out everything else.
Projection, welding goggles, or genuine solar filter film. That’s it. Don’t try anything else if you value your vision.
A bit late today in most of the western US, but locate the NASA site on this. Some have said use floppy disks and NASA does not say NO. They explain why some exposed film will work and some does not. Even some welding goggles don’t work.
Apparently some brief damage repairs itself. Some longer damage does not.
I once spent a few minutes looking at the full moon with a 5" reflector telescope. Never again - I bought a moon filter the next day. Sunlight will kick your ass, even when it is reflected off the moon.
You can get a pair of welder’s goggles (with a specific filter on it). Home Depot has them, I’ve used them, I can’t say for sure if the filter is the correct one.
Also, the last time I wanted to watch the sun (Transit of Venus I think), I ran to our public museum and bought a few pairs of Eclipse Sunglasses. They were like $3 each. They look pretty much just like this, they only thing you can see with them on is the sun.
I also took some pictures of it with an IR lens on my camera. Ya know what really hurts, looking through a telephoto lens (zoomed all the way in) and forgetting the IR filter isn’t on. I honestly thought I did permanent damage to my eye. It was such an intense/intimidate stinging like someone stuck a cigarette in my eye, and hurt for a few days. I’d imagine it’s pretty similar to what happens when a welder forgets to put his mask on. I hear they put potatoes on their eyes when that happens…I chose to skip that and just wait a few days, it went away.
Actually you can’t. I’ve tried it. It is still too bright.
You can use some welding goggles. They come in a variety of ratings.
And looking at the full moon can be safe, if your eyes are daylight-acclimated… but is really rough in the much more likely event that they’re not.
Yesterday I used my son’s welding goggles and mask. Turns out his mask was not nearly dim enough, and the goggles were almost dim enough, and the two together were perfect – that was for looking at the sun.
Which, as it turned out, was all I got. We were supposed to get partial occlusion here, but I sure didn’t see any, not even right at the maximum. I even double-checked with Google Sky and it showed the moon smack on top of the sun, with only a crescent of the sun showing. Ah well, we get a total eclipse next August, they say.
Next total eclipse for the US is August 21, 2017.