azimuth to hour angle conversion. Once again, the list proved to be a really
nice, helpful place!
I received several suggestions, ideas and some snips of code. Jim Morrision
gave me the actual code I wanted. Thanks, Jim.
Steve
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Monday, March 28, 2005 6:07 PM
Subject: [Fwd: Azimuth to Hour Angle code wanted]
I sent Steve some code for this problem, but I thought the group might
enjoy some details.
Calculating the hour angle from the azimuth angle given declination and
latitude is not as straightforward as it seems at first. The relevant
equation is:
sin h = sin lat sin decl + cos lat cos decl cos H
where h = altitude, H = hour angle from south, lat = latitude and decl =
declination.
The equation above can be solved for H, but you have to know the altitude.
Therefore, the problem becomes finding the altitude given lat, decl and
azimuth.
Edmond Gunther (1581-1626), who invented a quadrant known as "Gunter's
Quadrant" solved it in an interesting way.
1. Calculate the altitude when the declination = 0 (i.e. at the equator)
tan h0 = cos A / tan lat
2. Calculate an auxilliary angle from:
sin x = cos h0 sin decl / sin lat
3. Calculate the altitude, h, from:
h = x + h0 if A < 90
h = x - h0 if A > 90
The value for h can then be used to find the hour angle.
There are some details to attend to if it is neccessary to deal with
negative altitudes, which are seldom a factor with sundials.
Best regards,
Jim
From: Steve Lelievre <[EMAIL PROTECTED]>
Date: 2005/03/27 Sun PM 03:29:54 EST
To: [email protected]
Subject: Azimuth to Hour Angle code wanted
Hi,
I'm looking for some BASIC code (or, second-best, C code) that calculates
the hour angle from a known latitude, solar declination and azimuth.
If anyone has a tried and tested code fragment to share, I'd love to
receive
it. You'll save me an hour or two, and a headache.
Thanks,
Steve
----
Steve Lelievre
Halifax, NS
Canada
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James E. Morrison
[EMAIL PROTECTED]
Astrolabe web site at astrolabes.org
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