The few times I quickly looked at the sun when I was a kid it seemed to almost hurt my eyes which of course made me squint. Was this due to the intense brightness or the UV rays? And am I right in understanding that it’s the UV rays that cause blindness when looking at the sun?
To that effect, if it IS the UV rays that damage the eyes, could you just look at the sun through a piece of glass since it filters most UV rays out? And lastly, is looking at the sun through a mirror essentially the same (in terms of damaging effects) as looking at the direct sun?
Brightness makes you squint; UV does much of the damage. Even if you filter out all the UV, however, staring at the unattenuated Sun can still damage your vision, since the intense light can still damage retinal cells via heating. For all intents and purposes, looking at a solar mirror image is the same as a direct view with some small degree of attentuation in the UV–still far from safe.
You need a telescope of some kind to project an image of the sun. A common method is called eyepiece projection: you hang a screen a few inches or feet from the eyepiece. It is often done for demonstrations, but you have to make sure nobody misunderstands and tries to look through the eyepiece.
While working at an observatory hosting a public demonstration during the day, I did this. To underscore the hazard, I drew a frowning face on another bit of paper and used the light to burn holes where the eyes belong.
In retrospect, this probably didn’t have the right mix of encouraging hospitality.
For the record: do not look at the sun through anything that wasn’t specifically designed for that purpose. No smoked glass, no mylar, etc., and definitely not anything that increases the image, like a telephoto lens.
Also: It’s perfectly ok to look at a total solar eclipse without eye protection, but only during totality.
My inexpensive telescope came with a Sun lens (and I believe a Moon lens also). Small inserts with smoked glass to reduce the intensity of light. I’ve heard these are dangerous even though they are designed for that purpose, in that they can crack from the heat, and subject your eye to full strength sunlight.
I have a true solar filter for my camera. I have photographed several eclipses, plus the Transit of Venus (which took 6.5 hours) with telephoto lenses, and have never had related eye problems. I don’t think I’d trust a lens included with a cheap telescope, especially if it’s merely “smoked glass.” If you look through my solar filter, it’s almost opaque; you really can’t see anything except the sun.
I don’t know exactly what it’s actually made of. The problem is it goes on the end near your eye where the sunlight is concentrated. I believe there are safe ones which go on the large end of the telescope, similar to where a filter goes on a camera.
Nice. I set up my telescope without an eyepiece, and got a projected image on a sheet of paper. We took some pictures of that, but obviously not as nice as a direct photo. But it was fun for the kids.
>The problem is it goes on the end near your eye where the sunlight is concentrated. I believe there are safe ones which go on the large end of the telescope
ZenBeam is correct to point out an important difference between sun filters for the eyepiece and sun filters for the objective (that is, filters in front of the telescope). If the sun filter is in a zone of concentrated light, it will get hot, and might crack and let the concentrated sunlight flood your eye. I have heard this advice many times, though I haven’t actually heard of a case of an eyepiece filter cracking and blinding someone.
I think there are two important points to consider about looking directly at the sun. First, it isn’t bad to look directly at the sun. What’s bad is to stare at it. Your eyes are designed to be able to look at it some small fraction of the time. Hell, it’s the most prominent feature in the great outdoors our eyes evolved to see.
Second, there is a special situation with ultraviolet light. As I understand it, eyes are subject to damage by visible and by ultraviolet light. Since in the daylight environment where this damage was evolutionarily relevant, visible and UV appear in roughly a constant ratio, we don’t actually need separate means of detecting both. We evolved a pain and protection response based only on the visible part. The new modern wrinkle in all this is that it is possible to make sunglasses that knock the visible part way down without changing the UC part much. Such glasses would interrupt the pain mechanism without interrupting the UV threat this mechanism partly deals with. Using sunglasses that block as much UV as visible pretty much fixes this, and using sunglasses that are even better at blocking UV do even better for us.
>Not true – you can project the sun through a pinhole – no telescope needed.
Yes, you’re right, I stand corrected. Though you could also call a pinhole and a screen a kind of telescope, if you can call it a “pinhole camera”.
Also, sometimes you get accidental projections of the sun’s image, if there is a tiny hole someplace and an otherwise dark screen beyond it. This happens sometimes with the cord holes in Venetian blinds, and with tree leaves. There are nice pictures around of partial solar eclipses as seen by such accidental configurations.
