NavList:

Henry, you wrote:
"Isn't it really amazing how we seem to keep re-inventing the wheel. Didn't our "land bound" Professor Chauvenet give us the exact same number, i.e., +/- 10 arc seconds, in an 1868 paper on Astronomy - admittedly, however, he doesn't mention the matter of irradiation. Most of this stuff can be found in the literature of yesteryear."

Apples and oranges?

If anyone ever tells you that you should expect +/- 10 arcseconds in sextant observations with no further qualification, you should immediately ask, "what observations? what type of sextant? what telescope magnification? how many observations averaged?" There is no absolute number for the expected accuracy of observations, but there are some limits. The limit of the human visual system for standard resolution tasks (not vernier tasks) is about one minute of arc, slightly better in excellent conditions. If an observer gets unit magnification results for standard celestial navigation tasks un-averaged that are significantly worse than that, THEN something is wrong. Maybe the horizon is poor. Maybe there is some sort of operator error. Maybe even that ghostly apparition known as "Irradiation" is at work. Or maybe it's just a bad sextant.

As for Chauvenet, he had almost no experience in navigation. Though he was an exceptionally competent and meticulous mathematician, why would you trust his numbers on something like this? Are his works Scripture??

-FER

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