Re: Azimuth calculation/Wall declination

[Bill Gottesman]

About 10 years ago I worked out a simple method to measure wall declination using just a carpenter's square and an accurate watch.  The methods is described here http://www.precisionsundials.com/wall%20declination.pdf, and a simple windows program that does all the calculations for you is here http://www.precisionsundials.com/walldeclination.exe.  When I tested it out many years ago, I believe it gave results repeatable at different times and on different days to a few tenths of a degree. -Bill On 7/31/2011 9:57 AM, Andrew Theokas wrote: Fellow dialists:   I am using the following well known formula to calculate the sun’s azimuth for a particular time and location:   Azimuth= tan-1    (sin H/(sin φ*cos H – cos φ*tanδ)   where H= Sun’s hour angle φ= the latitude - 42.3 degrees δ is the sun’s declination - 18.62 degrees   The location is in Boston, USA or 42.3 degrees N and 71.04 degrees west   I am using the azimuth-azimuth approach to find the declination of a wall found here:   http://www.mysundial.ca/tsp/wall_declination.html   the time the measurement was made was 11:18 am (daylight savings time is in effect)   I can easily calculate that the azimuth with respect to the wall is 26.8 degrees.   Here is the problem: using two other independent methods I find that the wall’s declination is 20 degrees East.   So 26.8 degrees – Sun’s Azimuth should equal about twenty degrees.   But, using the above equation I cannot get an Azimuth value to work. One place where I might be in error is the value of the Hour angle which I compute to be about –16 degrees.   But you can also find the Hour Angle on line here at http://pveducation.org/pvcdrom/properties-of-sunlight/sun-position-calculator   Where might I be going wrong?   Many thanks for a reply!   Andrew Theokas     --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial

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