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Looking at the Sun for exactly the same period of time is less dangerous during an eclipse because a sizable percentage of the radiation, but not all, is blocke
by kobeya 9y ago
Looking at the Sun for exactly the same period of time is less dangerous during an eclipse because a sizable percentage of the radiation, but not all, is blocked by the Moon.
Where the danger comes in is that normally the Sun is so bright that if you mistakenly look into it your natural reflexes cause you to flinch away, prevent anything more than a momentary glimpse lasting fractions of a second.
During an eclipse the Sun is dim enough that you could stare at it without "visual pain" (for lack of a better term -- whatever you call something that is too bright) to such a degree as to cause instinctual look-away reflexes.
As a result if you were dumb enough, ignorant enough, or presidential enough, you could stare straight at the eclipse for seconds or 10's of seconds during totality. During that time it will not seem "too bright", but nevertheless your eyes will be focusing intensely damaging UV radiation onto your cornea, causing those cells to malfunction and die, which is what causes blindness.
That said, this is highly educated, rational crowd. I would not feel comfortable giving this explanation to a gathering of the general public because it can easily be misconstrued to mean "this guy says looking at the Sun during the eclipse is not as dangerous as everyone says it is" which has the exact opposite implication with respect to safety. I expect this is why the "looking at the Sun during an eclipse is more dangerous" meme got started -- it results in better safety.
- jl6 9y agoWhy is the light reduced by a huge amount during an eclipse but the UV is still at dangerous levels?
- deadmetheny 9y agoBecause the moon is in front of the sun. The brightness is reduced during partial coverage to the point that you won't reflexively look away anymore, but the UV is still there and still causes eye damage.
- deadmetheny 9y agoSo why am I being downvoted for answering a question, exactly?
- jstanley 9y agoI didn't downvote you, but the reason some did is probably because we want to know why the UV is still there. Merely restating that the UV is still there contributes nothing.
- amluto 9y agoAs I understand it, the relevant factors are the brightness per unit solid angle (aka surface brightness), the aperture (area of your pupil). The degree of danger for a given time spent starting at the sun is proportional to the product. The surface brightness of the sun is the same during a partial eclipse: each bit of sun is just as bright as if there was no eclipse -- there's just less of the sun visible. This is true in visible and UV, so the ratio of UV to visible light is unchanged. The problem is that everything gets darker, so your eyes dilate, which increases the danger. Also, partial eclipses are neat, so you're more likely to stare. During totality, it's a whole different ballgame. You can't see the bright part of the sun, and all that's left has much less surface brightness. I think it's roughly comparable to the moon.
- saltcured 9y agoThere's no appreciable wavelength-specific filtering going on in an eclipse since the moon has no atmosphere. (The corona does have a different spectra than the surface of the sun, but that's not the issue here. The corona is dim enough to look at.) The problem is that there is so much invisible energy in proportion to visible energy. So blocking a large portion of the sun's disk, so your eyes no longer detect too much visible light, still allows too much total energy which fries your retina when focused into a very small area by your eye's lens.
- mkstowegnv 9y agoAll the sources I know of [e.g. 1] say there is no danger looking at the "sun" during 100% totality, and I have stared at the corona for minutes each of all three times I have been fortunate enough to experience totality and I appear to have no visual damage (actually have been tested for unrelated reasons). Of course it is dangerous to look at the sun during the build up to totality - but I recommend not looking up until the corona appears anyway (shadow bands and the onrushing shadow are more exciting than Bailey's Beads). If you have any reason to believe otherwise please share your sources. [1] https://eclipse.gsfc.nasa.gov/SEhelp/safety2.html https://eclipse.gsfc.nasa.gov/SEhelp/safety2.html
- sulam 9y agoThey're saying this was an annular eclipse, not a total eclipse. In my opinion that would be dangerous to stare at, and I'd suggest the burden of proof would be on you if you disagree.
- planteen 9y agoYes, an annular eclipse is dangerous to look at at any time without protection. An annular eclipse by definition never reaches totality, since at maximum eclipse the sun is never 100% obscured. While the linked article discussed an annular eclipse, kobeya's comment makes it sound like looking directly at the sun during a total solar eclipse at toatlity is dangerous. This is wrong. It is not.
- acchow 9y agoDon't your pupils shrink dramatically when looking at the bare sun? Whereas they are quite open during a partial eclipse?
- planteen 9y ago> As a result if you were dumb enough, ignorant enough, or presidential enough, you could stare straight at the eclipse for seconds or 10's of seconds during totality. During that time it will not seem "too bright", but nevertheless your eyes will be focusing intensely damaging UV radiation onto your cornea, causing those cells to malfunction and die, which is what causes blindness. What you are saying is wrong during totality on a total solar eclipse (not an annular one). Your reference to Trump does not apply since he was not in the zone of totality. Did you view the August 21, 2017 eclipse in the zone of totality with glasses on? If so, I feel very sorry for you, you saw nothing. "When the eclipse is TOTAL, that is, when ALL of it is COMPLETELY covered by the moon, you can then look at it directly without eye protection. In fact, during those few brief minutes and seconds of totality, you MUST look at it without protection to see anything at all." http://www.eclipse2017.org/2017/viewing.htm http://www.eclipse2017.org/2017/viewing.htm