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Jim Wilson, you wrote:
"Having viewed the last six total solar eclipses, I can now worry about
the conditions immediately preceding totality."

First of all, I'm jealous. :-) Six total eclipses... very nice!

As for worrying, no, I wouldn't. The people who are at risk in those last few 
dozen seconds before or after totality are people who are unaware that they 
are looking at an eclipse. It's really very strange to me how long it takes 
for casual obervers to notice that there is an eclipse in progress (unless 
the Sun is near the horizon). I remember observing a 99% eclipse in Chicago 
years ago, and no one that I spoke to noticed anything wrong with the Sun 
though some did sense the "harshness" and "strangeness" of the sunlight on 
the landscape. And incidentally, the next time you see a 99% eclipse, 
consider that you're seeing as much sunlight and the same total brightness 
for the Sun as you would see on a sunny day from the rings of Saturn (10x 
further from the Sun, 100x fainter). Now as the eclipse passes from 99% to 
99.9% and then totality, quite suddenly casual observers will notice the Sun 
is "wrong" and they may start staring at it --it's rather spectacular at that 
point. The catch is that, while the total brightness of the Sun is greatly 
reduced and does not induce the normal "blink" reflex, the intensity of the 
light is quite unchanged and staring at it for a dozen or a few dozen seconds 
will cause permanent damage. Of course, any observer who has been forewarned 
will not make this mistake. Unfortunately, the media sometimes over-do these 
warnings and create the impression that an eclipse is beaming evil death rays 
at the unwary.

And you concluded:
"We were always advised to never look at the pre-eclipse sun through
binoculars, even with shades. But during totality, they're indispensable,
allowing us to see local sun activity like sunspots and solar flares. I
find that 10x20 are perfect, where the sun fills the field."

Looking through 10x binoculars at a 1% spot of the Sun is no different from 
looking at the full Sun with the unaided eye (except that the glass of the 
lenses --even without shades-- significantly reduces the UV portion of the 
spectrum). So for example, if you're looking at the very end of totality 
through binoculars and you suddenly see Bailly's beads (small bits of the 
Sun's disk visible through valleys and depressions along the limb of the 
Moon), you will not harm your eyes so long as you look away within a second 
or so --just as you would do if you glanced at the full Sun high in the sky 
without optical aid. Binoculars or telescopes make the image of the Sun 
LARGER but do not change its surface brightness, in the sense of either 
energy per square millimeter on the retina or energy per square arcsecond in 
the visual field. So if you're looking at a 1% bit of the Sun, then magnified 
by a factor of ten, its area either in square arcseconds, would be the same 
as the Sun normally. The total brightness of that 1% bit would be just the 
same as the full Sun with no optical aid. The magnification alone is 
responsible for this --there's no additional "enhancement" of the energy.

-FER



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