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I wrote:
> For instance, at 2014 March 19 at 1700 UT1, compare Moon LHA from N89 59
> 59 W000 00 00 to a GHA computed by subtracting the geocentric apparent
> RA from Greenwich apparent sidereal time.
>
> 220 01 11.6  topocentric LHA
> 220 01 11.5  RA - GAST

Last line should say GAST - RA, as the paragraph above says.

The topocenter should be near a pole to minimize parallax, because you
are trying to emulate a geocentric observation. Of course an observation
at a pole has parallax too, but the observer's displacement from the
geocenter is along Earth's axis. Therefore hour angle is not affected. A
terrestrial analogy is observing an azimuth from ground level vs. from a
tower directly above. Elevation is different, but not azimuth.

I chose the Moon for my example to make this more critical. The Moon's
maximum parallax is about one degree.

MICA is (or was, last time I looked) claimed to be suitable for
celestial navigation. But unless improvments have been made, it gives
unrefracted zenith distance in DMS.s format, a far cry from the
refracted DM.m altitude a navigator needs. Tinyac, with its elaborate
coordinate system options, was inspired by my disappointment with MICA.

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