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    Re: Azimuth Formula Questions
    From: Bill B
    Date: 2005 Oct 28, 17:37 -0500

    George wrote:
    > Here's the expression to use to obtain azimuth from its Tan. It presumes
    > that southerly latitudes and declinations are negative, that local hour
    > angle is measured positively Westwards 0 to 360 degrees, and that azimuths
    > are measured clockwise from North, 0 to 360 degrees.
    >
    > az = arctan (sin (hour angle) / (cos (hour angle) sin lat - cos lat tan
    > dec))
    >
    > Then to put az into the right quadrant, apply the following rules-
    >
    > if tan az was negative, add 180 degrees to az.
    > if hour angle was less than 180 degrees (i.e., to the West of the observer),
    > add another 180 degrees to az
    
    I notice another (longer) formula in the HO229 background section that also
    does not require Hc:
    
    tanZ = (cosd sinLHA)/(cosL sind - sinL cosd cosLHA)
    
    L is latitude
    d is declination
    
    Zn is determined as per 229 usual rules:
    North lat
    Z > 180, Zn = Z
    Z < 180, Zn = 360-Z
    South lat
    Z > 180, Zn = 180-Z
    Z < 180, Zn = 180-Z
    
    For the mathematically inclined, are there pros and cons for either formula?
    
    Bill
    
    
    

       
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