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You wrote:
"Does anyone know if the filters on sextants are really safe to view the sun
through? If modern sextants are safe and filter out harmfull _UV_ radiation
is the same true for older sextants?"

This has come up several times in the past few years. The short answer seems
to be that none of us really know for sure, and also none of us are blind
(yet) so you can count that as empirical evidence that the instruments are
safe. In my opinion, if you're concerned, it would probably be prudent to
get any sextant you plan to use extensively tested for UV transmission. This
shouldn't be expensive, and better safe than sorry, right? Consider also
that a sextant is usually used with a telescope. So in addition to the
shades themselves, you're usually looking through more than a centimeter of
glass (unless the optics are plastic), and glass does block dangerous UV
very effectively.

 -FER
Speaking of glass blocking dangerous wavelengths, I'm reminded of Richard
Feynman deciding to watch the Trinity Test (first atomic bomb). He was
sitting in a truck and he decided to watch WITHOUT protective dark glasses
since the glass of the windshield would stop any harmful UV light! He
figured that he was probably the only person who saw the first atomic blast
at its full brightness.


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