I’m not very familiar with MICA. I can’t seem to find semi diameter of the sun. Am I missing something?
Larry I have not looked at my MICA in years. With that being said you can find what you are looking
for in "The Astronomical Almanac " year xxxx. You can purchase the book from U.S. Govt. Pub.
Office ( http://bookstore.gpo.gov) you will want to look at page C6 - C21.
This should be online but since I get the book I have not checked that.
PS If you have some specific day (or days) I can put it here.
I'm very confused concerning your question. Mirror coronagraph (MICA) daily images at several observatories measure the inner solar corona with high temporal and spatial resolution in two spectral ranges: the well known green (~1.8 MK) and red (~1.0 MK) coronal lines at 5303 A and 6374 A respectively, which are the most accurate determinations of the sun's diameter in near real time. But that has little to do with how the eye lines up the sun's limb through a telescope.
If you're observing the sun for azimuth using tripod mounted theodolites the major effect on the sun's apparent diameter is its distance from the earth which varies annually, and is readily available in astronomic tables. It's easy to negate the effect of the sun's diameter and observer bias by inversion, observe the left limb, then the right limb, correct for time and average them. Similarly for altitude observations. Best if you're in a hurry is a Roelofs prism which is not affected by semidiameter.
I'll admit I'm an old timer; ran solar transit lines while working for the BLM (+-1°), then lots of solar alignment azimuths for microwave & cell tower sites which were maybe +-1/2°. Really tight azimuths required Polaris observations over several nights and could get to 15" or less.
But I realize those days are gone and a simple GPS procedure can determine azimuth with two stations a few thousand feet apart suffices now at much lower cost. So what is your question?
MICA is the Multiyear Interactive Computer Almanac from the US Naval Observatory. The USNO has mostly disabled their web site for over a year now with an overdue promise to update it. I got the program from Willmann-Bell Publishing, but later saw they didn't have it in stock.
The solar diameter can be found in MICA using Calculate / Configurations / Major Solar System Bodies
I found a previous thread about USNO and MICA. If you are interested in the program, note that it being a government-sponsored program I felt it okay to post it there for downloading (~125 megabytes).