11

I mean looking at a partial or annular eclipse, or before or after totality, and specifically the claim that it is more dangerous than looking into the sun.

I've heard two versions of this:

  • It is more dangerous because you'll be tempted to not look away (i.e. "a plain circle isn't interesting")
  • It is more dangerous, even for a brief instant, because the pupils are dilated.

Also, a surprising number of places don't explain at all, just saying it is dangerous to look directly at the sun without explaining why they're specifically repeating the warning for the eclipse when everyone knows not to look at the sun.

So is there any truth to this, and more specifically to the idea that it does permanent damage instantly (so if you're looking at the corona and totality ends, you won't get a chance to look away)

  • In a partial solar eclipse, the coolest thing to do is to look at the shadows of leaves, which act as pinhole cameras and project hundreds of partially-eclipsed suns on the ground. If you want to look at the sun, sunspots are cooler than partial eclipses (IMO) and if you want to see something awesome, use a hydrogen-alpha solar telescope and you can see the looping filaments, larger than the Earth, on the limb. – Larry OBrien Oct 24 '14 at 18:13
2

There is some truth behind this, according to Andrew Young, who cites numerous papers in his research:

Thermal damage (not really a “burn”) is possible under conditions of a partial eclipse, when only a little of the Sun is exposed, and the pupil opens up to adapt to the low overall light level; but it is unlikely in normal daytime conditions.

He then goes on explaining how cases vary depending on age (younger people are more likely to damage their eyes than middle-aged people due to filtering) and other factors, such as drugs that dilate the pupils.

To summarize:

So, did Galileo go blind from looking at the Sun through his telescope? The answer is, “Certainly not.”

Is it possible to injure your eyes by looking at the Sun? The answer is “Yes, but you have to work at it under normal circumstances.”

Can you become totally blind from looking at the Sun with the naked eye? The answer, according to Mulder, and from the cases of solar retinitis in the literature, is “No.”

Is solar eye damage permanent? The answer seems to be, “Only if it is severe.” About half the people with small scotomas recover from them completely after some months or years.

I don't intend to minimize the seriousness of solar eye damage; victims often lose the ability to read normal-sized print, for example. But draconian pronouncements that “you should NEVER look at the Sun” or assertions that you can become permanently and completely blind are an over-reaction to the actual hazard. Sunsets can be viewed safely, both with the naked eye and with binoculars, and most people are already aware of this.

Basically, don't look at the Sun for too long (more than a few seconds) during an eclipse; in non-eclipse times, looking at the Sun should be done in moderation.

12

It is more dangerous because the sun appears darker during an eclipse, making it more "pleasant" (or less unpleasant) to look at it for a longer period of time. Add to this the dilated pupils, and the fact that the retina itself doesn't feel pain and the adverse effects set on only after a couple of hours...

An excellent resource is this NASA Website, which states:

Even when 99% of the Sun's surface is obscured during the partial phases of a total eclipse, the remaining photospheric crescent is intensely bright and cannot be viewed safely without eye protection [Chou, 1981; Marsh, 1982]. Do not attempt to observe the partial or annular phases of any eclipse with the naked eye. Failure to use appropriate filtration may result in permanent eye damage or blindness!

  • I'd add that the blinding effect can set in as late as half an hour after exposure... So don't be fooled by someone looking at it next to you and saying after 5 mins everything's ok!!! – Count Zero Jan 7 '12 at 15:04
  • The NASA page just explains that looking at an eclipse is dangerous but says nothing about your "dilated pupils" claim, so I have to regard it as unsupported. In fact the NASA page doesn't address the specific question at hand: whether looking at the sun during an eclipse is more dangerous than at other times. So I had to down vote. – Nate Eldredge Oct 24 '14 at 13:49
  • I know this site has a strong requirement for sources, but is a direct source needed to show that a person's pupil will be more dilated during an eclipse? It'll be dark out (or at least, somewhat darker than full daylight), and so the eye will have compensated. – Doug Kavendek Oct 26 '14 at 5:37

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