The chapter on sun/eclipse viewing seems to imply that, during an eclipse anyway, the most dangerous thing about the sun is the brightness; however, in the anecdote about undeveloped film, it also says that nonvisible wavelengths damage the eye. What I still don't have a verdict on is: is it safe to view the sun in early dawn and late evening, when the sun is visibly dimmer?

How safe do you want to be?

An accidental glance at the sun might not cause problems, but the sun's rays focussed through a telescope without filters can sear flesh. OTOH, there are plenty of reports of naked eye sunspots, usually when the sun is low and diminished. Is that what you are asking about?

Yeah, all that's pretty much covered in the chapter, but I still don't know whether it's safe to look at the sun (that is, stare at it for extended periods) when it's right above the horizon, and, very dim.

Naked eye? It's safer than at noon. The longer you look the more the chance for damage. Problem is, you don't feel the damage. There's no warning when too much is too much.

It probably didn't hurt Galileo. Galileo, Solar Observing and Eye Safety

Oh, and ask your opthamologist, so I don't get sued.

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I presume the "non-visible wavelengths that damage the eye" referred to are ultraviolet wavelengths, which can cause snowblindness, cataracts and retinal damage. They're even more strongly scattered by the atmosphere than blue and violet wavelengths, so by the time the sun is sitting on the horizon looking yellow or red, the direct UV component is very small indeed.

Grant Hutchison

...as can focussing thru a magnifying glass...please don't do it....
not pleasant...

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clear skies

I use a white light solar filter, the kind that goes over a telescope to view sun spots, to sometimes look for naked eye sunspots. Just hold the filter up between your eye and the sun.

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"I'm as accurate as any psychic. And I'm a cartoon!" -- Squidward

"Arrrgh, the laws of physics be a harsh mistress!" -- Bender

What kind do you use? The one I have (Thousand Oaks TII) doesn't seem to work that way.

The intensity of direct sunlight far exceeds the eye's threshold and can damage the retina. A retina can not be reapired, as I understand. [Somewhat related, I once suffered arc burn on the eye due to uv reflection from a welding operation. It was quite painful. However, as Grant as stated, uv is very weak during low solar altitudes.]

Following an eclipse, a hospital in England, or was it Scotland, reported a couple of dozen people with eye complaints. IIRC, no permanent damage was found in anyone.

However, at very low solar altitudes (i.e. sunrise and sunset), the additional atmosphere reduces the amount of direct sunlight enough to be "safe", supposedly. Sunset will be safer than sunrise due to the additional dust and moisture raised by heating.

No surprise, observing sunsets is deemed theraputic by some - see solargazing. This is not something I would recommend.

As for some serious sunset sunspots, the mist from the Thames allowed Thomas Harriot in 1610 to see them, giving us the first pictoral record known.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

http://rainbowsymphony.com/free-3d-glasses.html
Send them a self-addressed, stamped envelope, a dollar bill, and a note saying you want Eclipse Shades, and you will receive a pair of cardboard glasses with solar filters for lenses, plus a pair of red-blue 3D glasses.
In regards to naked-eye viewing, the rule of thumb I heard is that if you have to squint, look away.

In regards to naked-eye viewing, the rule of thumb I heard is that if you have to squint, look away.

Interesting, the rule of thumb I heard is don't.

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