Next message: George Huxtable: "Re: Azimuth Formula Questions"
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
