Michael Karas wrote:
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General purpose, and they'll need gearing to the instruments.




The maths is pretty evil. I may use the 8052 for angle measurements, and pass the data to the PC for analysis.

HA and DEC to ALT and AZ

Extracted from http://www.xylem.f2s.com/kepler/altaz.html#twig04

Now we have the RA, DEC and HA for the object, and the Latitude (LAT) of the observing site, the following formulas will give us the ALT and AZ of the object at the current LST.

sin(ALT) = sin(DEC)*sin(LAT)+cos(DEC)*cos(LAT)*cos(HA)

ALT = asin(ALT)

sin(DEC) - sin(ALT)*sin(LAT)
cos(A) = ---------------------------------
cos(ALT)*cos(LAT)

A = acos(A)

If sin(HA) is negative, then AZ = A, otherwise
AZ = 360 - A

Note: Certain combinations of declination, latitude and altitude can
give a value of cos(a) that is larger than 1.0, so acos(A) will give
an error. Use the following formula in those cases (or perhaps instead
of the one above).

Y = -cos(dec) * cos(LAT) * sin(HA)

X = sin(DEC) - sin(LAT) * SIN(ALT)

Tan(A') = Y/X

Take the arctan(A').

If X is negative , then A = A' + 180
If X is positive, but Y is negative, then A = A' + 360
Else A = A'


...and I need the inverse too. It would be nice to type IN RA and DEC, and get a display showing error ON THE INSTRUMENT to the right position.

If anyone feels interested in joining in with this one they are more than welcome. It is a non-commercial project.

Incidentally the FASTEST you can possible move this is about 0.25 revs /second.

Steve