Celestial Navigation Sight Reduction

Intercept and Azimuth by the Law of Cosines Method

The USPS Navigation course makes use of the Law of Cosines method of Sight Reduction for reducing sextant sights. The equations used are as follows:

sin Hc = (cos LHA * cos Lat * cos Dec) + (Sin Lat * sin Dec)

cos Zc = (sin Dec - (sin Lat * sin Hc)) / (cos Lat * cos Hc)

where: LHA = Local Hour Angle
Lat = Latitude
Dec = Declination
Hc = Computed Horizon


Deg.

Min.

DR L: N S
DR Lo: E W
GHA:
Dec: N S
Ho:

Hc: Zn:
a: x 60 = miles

 


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