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anybody
2009-Aug-16, 07:38 PM
I accidentally took a passing glance of the sun about 5-10min before the sun set using my skymaster 15x70 binoculars. Could I have damaged my eyes by doing this?

I could look at the sun comfortably with my naked eye.

Oisin
2009-Aug-16, 07:47 PM
Yes you could! Never do this! If you start to feel heat in your eyes over the next 24 hours contact your doctor.

astromark
2009-Aug-16, 08:02 PM
This is a MUST NOT DO !... A inadvertent sweep across the field and you strike the sun... With a 15 X magnifacation you could have damaged your eye. If you can see your computer screen and there's not an ugly black hole in your centre of view.. then you may have gotten away with it. It would have made a strong impression and your sight may recover BUT, If some hour after the event you still see a dark spot in your vision you have damaged your eye. You should seek medical advice. Looking at the sun without a solar filter is madness. DO NOT DO IT.
With the unaided eye the sun at set or rise is not hard to look at because of the large angle you are not exposing your eye to a dangerous magnifacation. Do not use any magnifacation. It could be the last thing you see. Hissss.... Oops. :(

H4wkeye
2009-Aug-16, 08:03 PM
Imo i think you'll be fine,but NEVER EVER look at the sun through binoculars/telescope without propers filters.It can damage the eyes and the equipment.

matthewota
2009-Aug-16, 08:21 PM
The Sun's UV flux is dangerous even viewing sunsets or viewing the sun through smoke or haze, even if it does not hurt to look.

Take no chances and use proper equipment for solar observing.

anybody
2009-Aug-16, 08:28 PM
It's been about 4 hours since this happened and so far no signs of damage. hopefully I don't get a problem. :(

George
2009-Aug-16, 08:44 PM
Interestingly, using binocular or telescopes, one can not increase the surface brigthness (amount of light per unit area) of an extended object (non-point source object). However, the total area is greatly increased due to the magnification and much more of the retina will be exposed.

The big problem, as Oisin alluded to, is heat. The visible spectrum is greatly attenuated by thousands of times, which makes the Sun easy to look upon. But, this attenuation is much, much less for certain bands of the infrared. Thus, you won't feel this intense IR light, but it can be harmful, I think. Considering how many people enjoy watching the Sun go down and don't suffer eye problems, it may not be quite as bad as we think, but better to be safe than sorry.

astromark
2009-Aug-16, 10:11 PM
George... The way you have said that could be understood to be saying its OK, IT'S NOT !...
Those numbers on the end of your binoculars are telling you firstly the magnafacation and then the actual width of the optic lens. your 15 X 70 is as this ; That 70 mm of lens width gathers an area of light that your eye can not. Being at best 4 mm. That 70 mm is X 2 and then remember Pie X radius squared... Its a lot more light than your eye can naturally receive. To have it magnified some 15 times is suggesting to me a much to intense light image for you to look at safely.

I am pleased for you 'anybody' It seems you have escaped damage... you have been lucky. DO NOT LET IT HAPPEN AGAIN.

Romanus
2009-Aug-17, 12:15 AM
Since it was just a flash, you really lucked out. Had it been earlier in the day, even that brief glance might've been all she wrote.

Be very careful in the future, as everyone has said.

tdvance
2009-Aug-17, 12:18 AM
The usual "they" tell us to cap unused lenses when observing the sun through a filter, in case some kid wanders up and peeks into the finder, even.

I take a policy of looking nowhere near the direction of the sun through binoculars.

George
2009-Aug-17, 03:29 AM
George... The way you have said that could be understood to be saying its OK, IT'S NOT !... I made it clear that it is not wise.


Those numbers on the end of your binoculars are telling you firstly the magnafacation and then the actual width of the optic lens. your 15 X 70 is as this ; That 70 mm of lens width gathers an area of light that your eye can not. Being at best 4 mm. That 70 mm is X 2 and then remember Pie X radius squared... Its a lot more light than your eye can naturally receive. To have it magnified some 15 times is suggesting to me a much to intense light image for you to look at safely. Yes, it is unwise to use binoculars. But imagine if you had 15 easy to look at Sun's at Sunset. This would be 15x the amount of sunlight, but if one is easy to see, then all 15 might be just about as easy.

Frankly, when a setting Sun has been comfortable to look at due to a dusty sky, I've used binoculars to look at it. But, this is a bad idea because of the IR that I mentioned. I only did it once, and without eye deterioration that I am aware.

Again, it is impossible to take an optical system and increase the surface brightness of an extended disk. The larger the aperture, the larger the magnification. If you use very low powered eyepieces to increase brightness, then the exit pupil of the light beam is larger than the eye can receive, so this extra light doesn't enter the eye.

mugaliens
2009-Aug-17, 05:33 AM
Those numbers on the end of your binoculars are telling you firstly the magnafacation and then the actual width of the optic lens. your 15 X 70 is as this ; That 70 mm of lens width gathers an area of light that your eye can not. Being at best 4 mm. That 70 mm is X 2 and then remember Pie X radius squared... Its a lot more light than your eye can naturally receive. To have it magnified some 15 times is suggesting to me a much to intense light image for you to look at safely.

You're correct - it doesn't change the frequency of the light, but it vastly amplifies the photons per second impacting one's retina as compared to viewing it unaided. That's the same as moving one's hand closer to the fire. Too close, and you're burned.

Retinas can indeed burn, and can also suffer sunburn! The eye's cornea and lens, however, are remarkable UV filters (which is why people develop cataracts if they spend a lot of time outdoors without UV eyewear protection). Retinas can also IR burn, with both temporary and permanent damage, depending on the intensity and duration of the exposure.

Millions of people have suffered permanent reduction in visual perception as a result of looking at the sun, and most aren't even aware of it.

Try this as a test: On a dark, moonless, but clear night, find a faint star. Does it look brighter when you're not looking directly at it? If so, you've probably suffered from some damage/degredation to your optic disk.

George
2009-Aug-17, 02:49 PM
You're correct - it doesn't change the frequency of the light, but it vastly amplifies the photons per second impacting one's retina as compared to viewing it unaided. That's the same as moving one's hand closer to the fire. Too close, and you're burned. But this is true of any bright extended object, if we ignore that we can't get closer to the Sun in comparison and still benefit from the attenuation effects of our atmosphere unless we move the Earth closer, too.

A full moon can be brighter than a setting Sun in a dusty atmosphere. Based on mere photon flux (ignoring the IR band) can permanent damage occur if one uses binoculars in viewing the Moon? [Maybe it can, but not if it's setting on the horizon.] A full Moon with some altitude above the horizon is uncomfortable due to the total increase in flux, but there are setting Suns that are much weaker in flux than a full Moon.

So the problem isn't the gain in light flux using binoculars, assuming we have a very dim Sun at sunset. The problem that I see is the fact that the attenuation is not the same for the IR band and this can be quite bad for the eye. Viewing the Sun with binocs is still bad, but not due to the magnifying effects of the visible light, assuming, again, that we are looking at a very dim Sun on the horizon.


Retinas can indeed burn, and can also suffer sunburn! The eye's cornea and lens, however, are remarkable UV filters (which is why people develop cataracts if they spend a lot of time outdoors without UV eyewear protection). Yes, and it is quite painful, too. I suffered "arc burn" from merely looking at a wall instead of looking directly at an arc welding project. The UV reflections in just a few moments were enough to send me to the emergency room after a few hours at expired following the viewing event.


Retinas can also IR burn, with both temporary and permanent damage, depending on the intensity and duration of the exposure. I still think this is the big problem with using binocs.


Millions of people have suffered permanent reduction in visual perception as a result of looking at the sun, and most aren't even aware of it. Any evidence of this would be appreciated as there does seem to be some debate on this. I do recall a number of people in the UK who went to the hospital with eye problems following a Solar eclipse. Whether or not any suffered permanent damage would be interesting to learn about.


Try this as a test: On a dark, moonless, but clear night, find a faint star. Does it look brighter when you're not looking directly at it? If so, you've probably suffered from some damage/degredation to your optic disk. This is not a good test. Averted vision (http://en.wikipedia.org/wiki/Averted_vision) explains why looking directly at a star is not the best view of it.

hhEb09'1
2009-Aug-17, 03:06 PM
Try this as a test: On a dark, moonless, but clear night, find a faint star. Does it look brighter when you're not looking directly at it? If so, you've probably suffered from some damage/degredation to your optic disk.As George's link probably says, that would be true just because of the way the eye is built, not necessarily because of damage.

anybody
2009-Aug-18, 12:13 AM
It is comforting to read that although you've faced similar situation George, yet your vision hasn't been affected. I don't feel any damage or problems in vision and as I said it was a mere glance(a second or less).

Human eyes must have been built with some protection against nature.

It's been more than a day and I feel okay, tomorrow I have an eye checkup which happened to coincide with this incident.

I definitely won't be touching my binos any time before the sun has completely set.

A final question to you George, should I stop worrying now?

George
2009-Aug-18, 12:32 AM
A final question to you George, should I stop worrying now? I assume that you were comfortable looking at the Sun without binoculars at the time you looked through them. If so, then I see no real way you would be in trouble with the visible light. A few seconds of IR would not be a problem, IMO. [Nevertheless, don't be looking at the Sun with binocs.]

Either way, I think the answer is yes, you needn't worry. I looked at the Sun for 30 or 40 seconds in hopes to find some little sunspot -- I had no internet access where I was at the time to learn if any sunspots were there.

Besides I don't think there is much that could be done to help your eyes at this point anyway, but I am definetly no doctor.

WayneFrancis
2009-Aug-18, 08:24 AM
...

Human eyes must have been built with some protection against nature.

...

Yes there are multiple systems. Flash a bright light in someone's eyes and they'll either shut their eye lids or at least squint. Also the pupil contracts thus reducing the amount of photons that enter the eye and land on the retina.

An average human adult eye will try to contract the pupil to under 5mm2 with exposure to about 1 lambert.

Typical lighting in doors is about .05 lambert and the pupil can have a surface area of ~10mm2

Now magnifying an object in itself isn't a problem. And in actuality it is better to see a strictly magnified object then a non magnified object. This is because it spreads out the amount of harmful EM radiation. The thing is binoculars and telescopes also collect from a larger area and concentrate this in a smaller area. This mean more photons per surface area on the eye.

Evolutionary wise our eyes are perfectly fine for what they have needed to do. There was no way to significantly concentrate more EM radiation for most of our development. Thus protection from us being stupid and looking at the sun with binoculars has not had any chance to develop.

Think of it this way. When you go to the dentist and get an xray they only shoot xrays at a small part of your jaw to limit the amount of xray radiation you receive. This is because the more EM radiation you get, in this case xrays, the higher your chance of having cell damage to include cancer. If you have a very large objective lens compared to the ocular lens then you are effectively turning up the power. Say you have binoculars with 50mm objective lenses a 10mm ocular lenses then it would be like taking the xray machine and turning up the power by 25x.

Now some notes, a full moon that is "brighter" then a setting sun, Well I'd like to see that but even if it was possible the moon does not reflect all of the EM spectrum that hits it. So in essence the moon is like a optical filter.

So you're eye has evolved to handle certain situations but looking at the sun is definitely not one of these. It is hard for a person to judge if their eyes are damaged as our brain actually does a lot of work on what we take in. Look at a white wall in a room, change the lightbulb from a warm reddish emitting light to a cooler blue emitting light and your brain will still register the wall as white. The only way to catch this type of damage is to have proper tests done before and after and compare the results.

Basically, in the future, don't shoot your self in the evolutionary foot and if looking through binoculars or telescopes stay well clear of the sun and any highly reflective surface between you and the sun.

George
2009-Aug-18, 12:51 PM
The thing is binoculars and telescopes also collect from a larger area and concentrate this in a smaller area. This mean more photons per surface area on the eye. Binoculars will increase the photon flux, but they won't increase the no. of photons per unit area. This came as quite a surprise to me. We all know that we can burn leaves with a simple convex lens, but when we are looking at objects in focus it is a different story as to the concentration of light. [ Here's (http://www.bautforum.com/space-astronomy-questions-answers/46471-surface-brightening.html) a thread on this topic.] [Again, I am in no way suggesting we can look at the Sun with binoculars, but it is interesting that it is not quite as bad as we might think.]

WayneFrancis
2009-Aug-19, 02:05 AM
Binoculars will increase the photon flux, but they won't increase the no. of photons per unit area. This came as quite a surprise to me. We all know that we can burn leaves with a simple convex lens, but when we are looking at objects in focus it is a different story as to the concentration of light. [ Here's (http://www.bautforum.com/space-astronomy-questions-answers/46471-surface-brightening.html) a thread on this topic.] [Again, I am in no way suggesting we can look at the Sun with binoculars, but it is interesting that it is not quite as bad as we might think.]

Well there is obviously some confusion here and it might be with me but the way I read Ken G's posts is that for a given surface area when looking at the sun you will not increase the surface brightness. But the problem is we aren't concerned with the surface brightness in this case but the overall luminosity of the object. By having a larger collection area we ARE collecting more photons. This is a prime reason why having a telescope with a large diameter telescope gives you both brighter and clearer picture over all. CCD's show this effect very well. Take your mobile phone without a flash and take a picture at night. Now at the same time take a 35mm camera with a larger CCD then each pixel will receive more photons not only because of the larger sensor size but the larger area it is collecting from.

Going back to the Xray analogy it would be like saying that the lead smock you where didn't do any good because the brightness of the xray machine is still the same. Sure the brightness of the xray machine hasn't changed but you've increased you chance of cancer by the ratio of the amount of area exposed without the smock / the amount of area exposed with the smock.

Ah wait here is another example using photon flux. Solar panels typically generate a given amount of power for their surface area. A growing trend is to increase the power solar panels produce by using a solar concentrator. This focuses a larger area of sunlight onto the solar panel. This very definitely increase the amount of photons per unit area. I just noticed your first line


Binoculars will increase the photon flux, but they won't increase the no. of photons per unit area.
is like saying "I'll give you more candy bars but this won't increase the number of candy bars you have"

The photon flux is defined as the # of photons/sec/unit area
Φ= # photons / sec m2
seeing the area is defined by the size of your eye and that doesn't change and the time you look at the sun doesn't change that means there is a direct relationship between the photon flux and the number for photons per unit area.

astromark
2009-Aug-19, 03:30 AM
My telescope has a 240mm diameter light gathering width. That's its width not its area...the area is that times pie., :regardless of that detail, all that light is focused into a area 'smaller' than my eye's pupil. I do not except that my eye is not receptive of much more light than without my telescope. I see you agree its never safe to look at the sun without the proper filtering equipment. Then how do you contradict your self with that obviously wrong assertion that we are not getting more light. Read and take in what Ken and Wayne have said... they are right.

George
2009-Aug-19, 04:39 AM
Well there is obviously some confusion here and it might be with me but the way I read Ken G's posts is that for a given surface area when looking at the sun you will not increase the surface brightness. Yes. In other words we can not optically produce a square cm light beam that has a energy flux greater than a square cm found on the Sun. But it goes further than just that.

I disagreed with him for quite some time convinced that optical devices could brighten the surface brightness, but he refuted me at every turn. I finally bet him that I could burn a leaf faster with my gedanken experimental magnifying glass faster than he could without one if we were to go near the Sun to conduct our test, but he quickly thrashed me, in his typical Kurteous Ken way, of course :), but I managed to win on a very fortuitous techncallity. Nevertheless, he demonstrated that his leaf would, essentially, burn-up just as fast without the magnifying glass. It is an amazing thread, but it is a bit too long. [Don't tell him I think he won. :shhh:]


But the problem is we aren't concerned with the surface brightness in this case but the overall luminosity of the object. By having a larger collection area we ARE collecting more photons. This is a prime reason why having a telescope with a large diameter telescope gives you both brighter and clearer picture over all. Of course we do obtain much greater photon flux by having greater aperture (increasing as to the square of the aperture diameter).

There are a couple of points to consider regarding this however. For point sources, the result is that you will make them appear brighter since we are increasing the flux, but you are not increasing their apparent size.

But this is not the case for extended objects. Consider the Moon. If you were to use a 2x telescope it would be, essentially, the same as if you traveled half way to the Moon, right? [We will ignore inefficiencies and atmospheric effects.] Thus, we will have 4x (22) the amount of photon flux as we had when we viewed the Moon from Earth. But, and here's the kicker, how much larger does the Moon appear? It now appears 4x as large, and the net effect in surface brightness is what? Impressed? :) Both the flux gain and apparent size gain are identical since they both are inverse square law changes, so one can not make it look brighter with optical devices. [Telecompressors do help, but they are improving inefficencies and not getting us greater than the actual surface brightness that we see with our naked eye.]

But more aperture should do the trick, right? That's what big telescopes give us, don't they? The problem is that when you increase aperture you are forced absolutely to use larger magnifications. The important thing to understand here is that the exit pupil of the optical system should not exceed that of the entrance pupil size of the eye, if you want to capture all the photons. The exit pupil of a telescope can be expressed as simply the aperture diameter divided by the magnification (or focal length/f number). If you know your entrance pupil diameter, then you can easily calculate what magnification is ideal for matching these two pupil diameters by dividing the known aperture diameter by this pupil diameter.

For instance, using a large 100" (2540mm) telescope when viewing the Moon, where our eye's entrance pupil is say 4mm due to the Moon's brilliance, what minimum magnification can we use? M = 2540/4 = 635x. Any magnification smaller than this produces an exit pupil greater than that of our eye's entrance pupil, which means that the light beyond this 4mm opening will not enter. [Of course, surface brightness is not the only important thing so greater magnifications are common.]


CCD's show this effect very well. Take your mobile phone without a flash and take a picture at night. Now at the same time take a 35mm camera with a larger CCD then each pixel will receive more photons not only because of the larger sensor size but the larger area it is collecting from. CCDs are a great example of the way to get around the problem with the eye. They can simply absorb photon after photon with greater exposure times, which the eye can not accomplish.


A growing trend is to increase the power solar panels produce by using a solar concentrator. This focuses a larger area of sunlight onto the solar panel. This very definitely increase the amount of photons per unit area. Yes, this is identical to my earliest example of burning leaves with a magnifying glass (here on Earth and not the trip to the Sun experiment). But this is not imaging, which is our goal with binoculars and telescopes. If you try projecting images of the Sun with any sized magnifying glass, you will see that it will never be as bright as if you were to unwisely view the Sun with your naked eye.


...is like saying "I'll give you more candy bars but this won't increase the number of candy bars you have.I am saying that if you are underneath a glass coffee table and cover the coffee table with candy bars, you will not be able to see the candy bars that are stacked above the first layer. [Not a close analogy, but I like candy bars. :)]


The photon flux is defined as the # of photons/sec/unit area
Φ= # photons / sec m2
seeing the area is defined by the size of your eye and that doesn't change and the time you look at the sun doesn't change that means there is a direct relationship between the photon flux and the number for photons per unit area. Hopefully, I have answered this by addressing the inverse square law and how it applies both to the flux and to the apparent size. I'll be happy to elaborate further because I was quite surprised that big telescopes could not increase surface brightness.

My interest at the time was to use larger scopes to improve surface brightness in order to excite our color cones enough to reveal the rich colors in nebulae. But guess what? We can't do it, though bigger scopes at high altitudes do reveal some colorful nebulae here and there.

George
2009-Aug-19, 04:57 AM
My telescope has a 240mm diameter light gathering width. That's its width not its area...the area is that times pie., :regardless of that detail, all that light is focused into a area 'smaller' than my eye's pupil. I do not except that my eye is not receptive of much more light than without my telescope. I see you agree its never safe to look at the sun without the proper filtering equipment. Then how do you contradict your self with that obviously wrong assertion that we are not getting more light. Read and take in what Ken and Wayne have said... they are right. For a 240mm, if you use an eyepiece that yields less than 34x magnification, then your scope's exit pupil will exceed your eye's entance pupil. Thus, if you are looking at the Moon at 34x, you will not see all of it through your eyepiece, thus you will only see a portion of the Moon. Also, as you increase your light flux with greater aperture you are also increasing the apparent size. You can not increase the flux greater than you increase the apparent size, which is the heart of the problem for trying to make extended objects brighter.

I should say that when we do look at something large and bright like a full Moon using binocs and telescopes, that even small magnifications will fill more of they eye's retina, which increases the total response of the eye and adds to the overall discomfort. Going to greater and greater magnifications will cause the Moon to become more dim, as we all soon learn from experience.

astromark
2009-Aug-19, 05:09 AM
I have read this thread of yours George., and think I have followed your points well. Your understanding IS as mine and it looks like you DO understand this as we do... Its just the way you are saying it. Would you without any distraction just agree that my eyes entrance pupil is but 4mm., and that the telescope with 100" or 2540mm of light gathering potential is going to burn your leaf quicker than a non magnifacation, with the naked eye would... ?
Understanding that yes, spreading the intensity and then enlarging it would serve to reduce some of the intensity. It will still burn your leaf... Mark.

astromark
2009-Aug-19, 05:46 AM
Oops... my post #23 was actually posted before my page updated to see your #22... and I can not find fault with any of that...:)

mugaliens
2009-Aug-19, 07:59 AM
Exactly - if it hurts, don't do it! If you squint, your eyes water, they hurt, whatever, STOP!

Common sense, people.

NorthernBoy
2009-Aug-19, 09:39 AM
It's been about 4 hours since this happened and so far no signs of damage. hopefully I don't get a problem. :(

I just realised that I gave medical advice in response to an old post, which is clearly now non-urgent, hence this edit to remove it...

George
2009-Aug-19, 12:22 PM
Exactly - if it hurts, don't do it! If you squint, your eyes water, they hurt, whatever, STOP!

Common sense, people.
Yes, we have a great mechanism that gives us warning... discomfort or pain. :)

This same logic, however, can be misleading. If the Sun is comfortable to look at on the horizon and no brighter than a full Moon, is it safe to look at? Our common sense says it is ok, but I am fairly sure the IR must be taken into consideration, which the common sensory system in our eye is not able to warn us about.

anybody
2009-Aug-19, 02:32 PM
I came back from my eye exam. The doctor said that my eyes are fine. My power became worse though, but that's natural at my age. He told me "to live life naturally".

I feel better now.

To participate in your conversations about the danger of the sun. The sun is obviously dangerous at midday since your eye CAN'T even look at it so forcing your eye to do so is obviously wrong.

However, I read that gallilleo observed the sun at sunset (until a projection method was available) and it wasn't reported that he had any eye problems in his biography until he got cataracts later and became blind before his death.

My question - can you burn a piece of paper(or anything) at a dim sunset (like the one I faced) with or without a magnifying glass?

I doubt it, yet i haven't tried it.

Peter B
2009-Aug-19, 04:07 PM
Well, a couple of days ago, my wife and I were able to have a good look at the Sun for quite a few seconds. It was a foggy morning, and when the fog was just the right thickness, we could see the Sun as a wonderfully smooth ball in the sky.

I've exploited Canberra winter fogs in the past to observe the Sun, including seeing some sunspots.

mugaliens
2009-Aug-19, 07:29 PM
[QUOTE=anybody;1554951]My question - can you burn a piece of paper(or anything) at a dim sunset (like the one I faced) with or without a magnifying glass?[/quote

Given an appropriately designed magnifying glass, you can burn an object with a simple, single candle.

Edit: I've seen it done, igniting paper, with the candle at one focus of a 3D ellipse interior mirror, and the paper at the other. The only lens was a simple one around the paper to reduce the image of the candle to a pinpoint.

George
2009-Aug-19, 09:28 PM
I came back from my eye exam. The doctor said that my eyes are fine. My power became worse though, but that's natural at my age. He told me "to live life naturally". That's nice to hear.


However, I read that gallilleo observed the sun at sunset (until a projection method was available) and it wasn't reported that he had any eye problems in his biography until he got cataracts later and became blind before his death.It is certainly possible Galileo did view some setting Sun's directly. I think it may have been one of Galileo's students that soon showed him that a projection screen could easily be used so no direct viewing would be necessary.

There is a slight chance that Galileo may have had eye trouble at a younger age, prior to college, because his father used this excuse to pull him out of his commitment into the clergy. [He wanted his son to be a doctor. Galileo happened to be the name of a recent ancestor who was a famous doctor. Our Galileo's family (grandparents?) changed their last name to Galilie to gain the recognition. Our Galileo was, of course, named after him, thus both his first and last name were a result of this earlier doctor relative. :)]

Interestingly, Kepler was known to have eye problems. This may have been the reason Galileo would not send him one of his telescopes, contrary to Kepler's request. [Kepler eventually obtained one from a 3rd party.]

anybody
2009-Aug-20, 12:44 AM
I asked about a dim sunset not a candle, mugaliens.


That's interesting George.

WayneFrancis
2009-Aug-20, 03:06 AM
I asked about a dim sunset not a candle, mugaliens.


That's interesting George.

Ummm what do you think is the big difference for between the 2 for the purpose of this experiment.

I think it is meant that the amount of illumination isn't as much as you would thing to get something actually burning.

WayneFrancis
2009-Aug-20, 03:15 AM
...
However, I read that gallilleo observed the sun at sunset (until a projection method was available) and it wasn't reported that he had any eye problems in his biography until he got cataracts later and became blind before his death.
...

Do you not think that frequent direct observations of the sun could have aided to his cataracts? More importantly constant direct observation is more likely to slowly damage your retina over time. I don't know about you but I can't pinpoint at what time I needed glasses. I do know that when I got them I realised I didn't see a lot of detail that normal 20/20 vision provide, ie individual leaves on a distant tree opposed to a general green blur. Even now with old prescriptions I can very well but I definitely notice the difference between old and new prescriptions when viewed on after another.

Blindness most often isn't a sudden thing. It gradually builds.

That said I'd like to see the result of a few measurements that actually measure a wide EM spectrum from the setting sun. Then we could actually make a better informed decision when we go to watch the sunset. :)

George
2009-Aug-20, 02:17 PM
Do you not think that frequent direct observations of the sun could have aided to his cataracts? That's a good question.

The UV from the Sun is known to contribute to the formation of cataracts, and other eye problems. But a setting Sun has very little UV due to Rayleigh Scattering especially.

What would interest me is the degree of damage a setting Sun's IR can do to the eye.

Another question of interest is the range of Moon's reflectance for the IR band. I know it is very low, 0.1% for certain portions, but I haven't found much for the near IR portion of the spectrum.

If the risk of eye damage from IR is very negligible, then what harm could possibly come from observing a very dim setting Sun that happens to be less in apparent magnitude than the Moon?

My guess is that the IR issue is less than the concern we have for ever recommending to someone that they observe the Sun with binoculars or telescopes since many setting Sun's are still too bright.


That said I'd like to see the result of a few measurements that actually measure a wide EM spectrum from the setting sun. Then we could actually make a better informed decision when we go to watch the sunset. :) An excellent request. The spectral irradiance data sets for the setting Sun and Moon are out there, no doubt, that will give us the answers we need. Hopefully, someone here will chase it down for us.