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Quote:And, unless I'm mistaken, that would simply require an elevation roughly equivalent to the longitude, and then calculating the magnetic deviation of that location so that I can point the object at the north pole.
Quote:drat....I always get those two mixed up..
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Quote:Ahhh. Reverse navigation eh?
Quote:A quick "sloppy" formula for the local sidereal time at Greenwich for 2013 is99.8+360.9856*DoY where Doy is the Day of the Year for 2013. So April 21, 2013 at 2100 (9pm CDT) is 111+21/24+5/24 = 112.0833, then 99.8+360.9856*112.0833 = 40560.27deg = 240.27deg The local sidereal time is 240.27 + L where L is your longitude (+ = East, - = West). For me at W97 the answer is 240.27+(-97) = 143.27 = 9.55h RAThe Hour Angle = H = local sidereal - RA Polaris[expressed in degrees or 15*(h+m/60+s/3600)].Once you have the Hour Angle, the latitude, and declination the Azimuth and Altitude can be found from standard formulas.RA Polaris is 41.98deg, Dec Polaris is 89.32deg, and my Latitude is 33Ntan Az=sinH/(cosH*sin(Lat)-cos(Lat)*tan(Dec)) [add 180 deg to AZ to be reckoned from North]sin Alt=sin(Lat)*sin(Dec)+cos(Lat)*cos(Dec)*cosHH=143.27-41.98 = 101.32degtan Az=sin(101.32)/(cos(101.32)*sin(33)-cos(33)*tan(41.98)) Az=179.2+180=359.2degsin Alt=sin(33)*sin(41.98)+cos(33)*cos(41.98)*cos(101.32)Alt=32.9degBut I kinda agree with Glenn on this one.Ed
Tom Karpf (tkarpf) Vice President, Astronomical Society of Greater Hartford www.asgh.org
Quote:Ok. But how does this formula get from 40560.27deg to 240.27deg?
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Quote:I'm trying to figure out how to write a formula to calculate the number of degrees from magnetic north to rotate.
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Quote:Even most old surveying compasses only measure to the nearest degree and modern hand held compasses measure to the nearest five degrees.
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Last but not least, telescopes.
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Quote:Quote:Even most old surveying compasses only measure to the nearest degree and modern hand held compasses measure to the nearest five degrees.I think that's pretty pessimistic; I can definitely get +-2 degrees with a regular hand-held compass, and probably better. Five degrees is a long, long way!Now that the requirement to find Polaris has been removed, this becomes simply what people do most with compasses: attempt to determine true north.
Quote:Quote:Even most old surveying compasses only measure to the nearest degree and modern hand held compasses measure to the nearest five degrees.
I think that's pretty pessimistic; I can definitely get +-3 degrees with a regular hand-held compass, and probably quite a bit better. Five degrees is a long, long way!
Having said that, I agree with the rest of your post; I don't see any point in this particular exercise.