# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Z tangent formula
From: Bill B
Date: 2005 Feb 16, 17:52 -0500

```George

Regarding a formula you gave for finding azimuth:

"This formula is-

Tan Z = sin (hour-angle) / (cos (hour-angle) sin lat - cos lat tan dec)

and the rules for putting Z into the right quadrant, 0 to 360, clockwise
fron North, are-

If tan Z was negative, add 180 deg to Z. If hour-angle was less than 180
deg, add another 180 deg to Z."

By hour-angle I assume you mean local hour angle?

I was also having trouble sporting out the parenthesis.  Should the formula
look like the following, if I let ha= (hour-angle)?

Tan Z =              sine ha
_________________________________________

(cos ha * sin lat) - (cos lat * tan dec)

Thanks

Bill

```
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