NavList:

Dale, you asked:
"Is there any good account for the origin (or derivation) of the phrase "clearing the lunar distance," with the emphasis on "clearing"?"

I think it's pretty straight-forward (no obscure meaning) though it's certainly an old-fashioned sense of the word "clearing". The more complete expression is to "clear the distance ... of the effects of parallax and refraction" which you can find at least as far back as the first volume of the Nautical Almanac and Astronomical Ephemeris for the year 1767. Here "clearing" simply means, more or less, "removing from" or even "cleansed of". This expression remains in modern celestial navigation where altitudes are "cleared" in the sense that observer and observation-dependent factors are removed from the altitudes.

-FER
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