Will just a glimpse (less than a second) of sun during partial solar eclipse damage eyes?
This doubt arose when I thought that on Normal Days, at least I have observed bright sun while going outside, going to office, in park etc. for less than a second. It happens almost daily. Not deliberately but that's how things work I guess. Similar example is playing cricket. Many times sun comes in the way of ball in the air and again I have a glimpse of sun. To me, it is very common as I've seen in international cricket matches on TV.
On the other hand, in case of the days of Solar Eclipse, on one or two occasions, when the sun wasn't very bright due to clouds, I've deliberately observed the partial eclipse just for a glimpse, just to confirm it's actually cut. And I confirmed it. (How fast it was? It was not like I stood still and observed the sun for less than a second and then closed eyes. It was like this: I started moving my head and sight from earth surface and in a faster way moved my head towards sun and without any break, stopped at safe location on earth again where there was no sun). And it did literally no harm to me.
So my doubt is:
Why there's so much theories that you must not stare sun even for less than a second or even a glimpse by mistake? If you see news on eclipse day, you'll see full news about this. But on any other normal day, no such news. Is there something special, something more bright on solar eclipse day? Will it damage eyes?
On normal days, people are significantly less likely to attempt to spend minutes staring into the sun, and the damage the sun does to your retina is painless.
@PM2Ring that comment is too hard for me to understand. Also, unfortunately the question doesn't answer my question at all.
When the eclipse is near totality, the sky is dark, so your pupils dilate, letting in more light. But the light rays coming from that small sliver of Sun are just as bright as normal, and have the same proportion of ultraviolet as full sunlight. I'll put this into a proper answer.
@Vikas Yes. The retina has no pain nerves, so the typical reflex response "That hurts, I should probably stop doing it" is not generally in effect for retinal damage caused by looking at the Sun.
@PM2Ring are you sure sky is dark when there's 99.5% solar eclipse, sky is dark? I have pictures of yesterday's total solar eclipse. I could still see sharp shadows of trees and objects. The light was less but it wasn't dark.
If the sky isn't dark, then your pupils won't dilate, and so it's just the same as glancing at the Sun at the same altitude (that is, the same angle above the horizon) on a non-eclipse day.
Variants of this question have been asked multiple times on Physics Stack Exchange. Here is a starting place: https://physics.stackexchange.com/questions/353019/is-looking-at-an-eclipse-worse-than-looking-at-the-sun
Humans are very good at adapting to changing light conditions. By the time things start _looking_ dark during an eclipse, the light reaching you is already about 1/100th of normal daylight - two orders of magnitude less light. I hope you see why this could be a problem for your eyesight :) And of course you can see shadows just like normal; the light in shadows still comes from the Sun. The ratio between the part in direct sunlight and the part in ambient sunlight (i.e. refracted by the atmosphere, basically) is different, but not by a lot.
You're probably confused by associating "dark" with cloudy skies. When it's overcast, there's essentially no direct sunlight reaching you. Much of the incident light is reflected back into space (it gets dark), but almost all of the light that makes it through comes from the atmosphere, not directly from the Sun. Thus, there are no shadows - all of the environment is illuminated from the same source, with the same brightness. The same isn't true at all when dealing with an eclipse.
Humans have been *accidentally* glancing at the sun since they first evolved, and they have an "automatic blink reflex" that prevents that from causing eye damage. If you *deliberately* look at the sun in any conditions, you are overriding that automatic protection.
The other issue is that the speed at which the brightness increases after the mininum of an eclipse is very fast, compared with sunrise or sunset, if the sun is high in the sky. I have seen one total eclipse "live", and after 2 minutes of totality, I found the rapid increase in brightness in the few minutes after totality was actually painful, even when *not* looking directly at the sun. The brightness change from switching on a light bulb in a dark room is several orders of magnitude smaller.
Glancing at a partial solar eclipse is about as dangerous as glancing at the Sun on any other day. If you look at the Sun a few minutes after sunrise or a few minutes before sunset, when the Sun's altitude is low, the light is filtered through a lot of air, and most of the ultraviolet is scattered, so it's a lot less dangerous than looking at the Sun in the middle of the day. However, during an eclipse, people tend to look at the Sun for more than just a few minutes, and that's not healthy for the eyes.
The big danger of looking at a solar eclipse without proper protection occurs when it's a total (or nearly total) eclipse. When the eclipse is near totality, the sky is dark, so your pupils dilate, letting in more light. But the light rays coming from that small sliver of Sun are just as bright as normal, and have the same proportion of UV (ultraviolet) as full sunlight. Those UV rays can cause a lot of damage to the retina very quickly, and that damage can be permanent.
slightly related (but about cameras): Are there industry standards or specs for image sensor resistance to damage from intense light?
Is there reason to believe it's any more damaging than stepping out of a dimly-lit indoor room with no windows into the outdoors and immediately glancing at the sun?
@R..GitHubSTOPHELPINGICE It's probably pretty similar. Or looking directly at the Sun through a crack in the curtains of a dark room. But I Am Not An Eye Doctor.
I'm afraid I feel I was more curious about knowing if we look at the sun the way I explained in question, will it damage eyes?
@Vikas There's nothing happening on a solar eclipse day that makes the Sun more dangerous than normal, apart from the thing I mentioned about having dilated pupils because of the darkness when the eclipse is very close to totality.