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Re: getting GHA from MICA
From: Paul Hirose
Date: 2014 Mar 19, 14:47 -0700
From: Paul Hirose
Date: 2014 Mar 19, 14:47 -0700
Sean C wrote: > Question: Is calculating the sidereal time and then the apparent geocentric equator of date position the only way to get the GHA of a body? I don't have the latest MICA version, but 2.0 has "Apparent Topocentric Equator of Date (LHA, Dec)" as one of the choices for position type. In theory, that will give you GHA if the topocenter is very close to a pole and at 0 longitude. 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 I converted LHA from hours to degrees. If you set the topocenter at exactly 90 north, MICA's LHA is a couple degrees in error. Of course one could argue that LHA and azimuth are undefined at a pole. However, my software does the common sense thing and computes as if you were on the specified longitude and an infinitesimal distance away from the pole. That happens with no extra effort by the programmer if the coordinate transformations utilize vectors and rotation matrices. --
