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Today's Weather
#46
(08-21-2017, 07:48 AM)Coke6pk Wrote:
(08-20-2017, 08:02 PM)Canard Wrote: It goes without saying, but since nobody's said it yet, you're not supposed to look directly at it at all, if you don't have special glasses.

Now I'm not trying to play devils advocate, but since I'm not a doctor, just some clarification....

I have looked at the sun in my life, but I don't think I have ever stared at the sun.  If someone were to take cursory glances at the eclipse, I'd assume this was safe.  [Normally there is nothing compelling to watch in order to stare, the eclipse being an exception].

Am I right, or is the sunlight peeking out from behind the sun more lethal than normal sunlight?

Coke

EDIT : As I typed I see ViewFromThe42 explained the difference.  Thanks!

I am also not a doctor but I'm not sure I believe the pupil explanation, the pupils contract quite quickly.  There are other light sensitivity effects that take longer to adapt too.  And further, I've also looked at the sun as I walked out of the house before, also without apparent ill effects.

https://arstechnica.com/science/2017/08/...rotection/

There are two types of damage.

The infrared light from the sun will scorch the fovea, the central part of the eye with the densest area of photoreceptors.

Also, 'photochemical toxicity', where the light causes chemical reactions in your eye (this is how one see's anyway, but the sun is so intense, the chemicals end up building up), which release various damaging chemicals, which will degenerate the retina.  This is apparently the most dangerous type of damage.

The harm that is done is not what one might expect.  Nobody ever has "holes" in their vision.  Or more to the point, everyone already has holes in their vision https://en.wikipedia.org/wiki/Blind_spot_(vision) and our brains simply ignore them, so even if you stared at the sun and burned out a part of your retina, you wouldn't see a 'hole'.  This is because our eyes do not work like a camera.  Our brain does a great deal of processing on our visual experience.  Vision is a very interesting topic.

In fact, I suspect this is perhaps the real problem difference between looking at the sun during an eclipse and having the sun within your field of view as part of your normal day is that when you look *at* something you focus the fovea of your retina on it.  That is the part of the eye with dense cone cells which works to see detail.  If you damage this part of your eye, you will have complete vision, but will be unable to see any details, recognize faces, or any of the important things we want to see.

Nevertheless, there is no reason to look at the sun when building a solar projector is so easy: https://www.youtube.com/watch?v=vWMf5rYDgpc

But you probably won't go blind if the sun happens to pass within your field of view during the eclipse.
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#47
In seven years (2024) we will be on the edge of a total solar eclipse.   Below is a map from CSI (at bottom of page).

   
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#48
(08-21-2017, 07:48 AM)Coke6pk Wrote:
(08-20-2017, 08:02 PM)Canard Wrote: It goes without saying, but since nobody's said it yet, you're not supposed to look directly at it at all, if you don't have special glasses.

Now I'm not trying to play devils advocate, but since I'm not a doctor, just some clarification....

I have looked at the sun in my life, but I don't think I have ever stared at the sun.  If someone were to take cursory glances at the eclipse, I'd assume this was safe.  [Normally there is nothing compelling to watch in order to stare, the eclipse being an exception].

Am I right, or is the sunlight peeking out from behind the sun more lethal than normal sunlight?

Coke

EDIT : As I typed I see ViewFromThe42 explained the difference.  Thanks!

Non-expert here. I think part of the issue is that it is easy to look at the eclipsed sun, whereas it is quite uncomfortable to look at the normal sun. If you forced yourself to stare at the normal sun you would do severe damage to your eyes, although a quick glance won’t do much if anything. But near totality, it’s no problem to stare at the sun — meanwhile your eyes are getting damaged.

I’m not sure how important this part is, but remember too that there are invisible light frequencies (UV) which I understand cause the worst damage. They aren’t necessarily affected exactly the same as the visible frequencies.
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#49
(08-21-2017, 10:07 AM)jgsz Wrote: In seven years (2024) we will be on the edge of a total solar eclipse.   Below is a map from CSI (at bottom of page).


that's a great map, I was thinking of heading to long point that day, but it looks like fort erie would be a much better choice.
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