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    Re: Parallax in azimuth
    From: Peter Monta
    Date: 2020 May 25, 01:13 -0700

    One could observe the leading limb of the Moon for an azimuth, but would anyone bother?

    Surveyors might.  The solar limb is (was?) a traditional observation for azimuth in survey networks; Sokkia's "Celestial Observation Handbook" has some details.  Now, the lunar ephemeris is not going to fit into a small booklet, but the principle is there.  A theodolite's measurement noise might be 1 or 2 arcseconds, so the correction would matter, provided the surveyor could handle the timing requirement of ~100 ms in UT and has access to an ephemeris.

    I played around with daytime stars with the theodolite some time back; it's a lot of fun.  As I recall, stars down to magnitude 1.5 were visible in the 50 mm 40x scope; I'm sure an eyepiece camera could do even better.  (I tried several times for Polaris and just could not see it.)  So there are a fair number of azimuth references available in daytime in addition to the Sun and Moon.  (But real surveyors work at night.  Atmosphere is steadier.)


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