I am new to the sundial list and am building a sundial based on an example in Albert Waugh's book Sunidals Their Theory and Construction. My problem is in computing lines of declination, however. I live in Washingotn DC at approx. 39d West Lat. 77d N Long. I'd like to trace the sun's path for one particular day, July 4, 1998. I believe the declination for that day is very close to +22d.54.34.9 and the sun's altitude in degrees for various times are as follows: 4:00 -8.5 5:00 1.6 6:00 11.9 7:00 23.1 8:00 34.6 9:00 46.3 10:00 57.6 11:00 67.7 12:00 73.7 13:00 71.0 14:00 62.1 15:00 51.1 16:00 39.5 17:00 27.9 18:00 16.5 19:00 5.7 20:00 -4.6 The book states that all I must do is take the cotangent of these altitude numbers and multiply by the height of my perpendicular style (which is 2 inches) then measure out to the appropriate hour line. My problem is that I cannot figure out what a cotangent is or how to calculate one. Please help and send a detailed formula with examples so I can compute the cotangent for other numbers. Thanks a lot in advance.
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