# NavList:

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

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Re: Sight reduction formulae
From: Stan K
Date: 2011 Dec 1, 14:51 -0500
Randall,

In my previous e-mail I should have added that
1) in the sin formula, that sign is always +
2) in the cos formula, that sign is always -, but the formula is missing parentheses
cos Az * =  (sin dec +/- (sin Hc x sin DR lat)) divided by (cos Hc x cos DR lat)

Stan

-----Original Message-----
From: Randall.F.Morrow <Randall.F.Morrow@kp.org>
To: NavList <NavList@fer3.com>
Sent: Thu, Dec 1, 2011 2:37 pm
Subject: [NavList] Sight reduction formulae

I'm trying to do sight reductions by calculator but I'm having trouble with the sign(s).     On example I have found is below but I have seen others in which the sign(s) do not change with same versus contrary latitude and declination.    Is this correct?   (I don't remember where I found this)
Thanks, Randy

sin Hc = (cos LHA x cos DR lat x cos dec)  + or - (sin DR lat x sin dec)
Note: use + if lat and dec are same names.
cos Az * =  sin dec +/- (sin Hc x sin DR lat) divided by (cos Hc x cos DR lat)
Note: use + when lat  and dec are of opposite names.
* Remember Az is the azimuth angle. To get Zn (Azimuth) apply the rules:
Northern Lat:  LHA > 180 deg. Azimuth = Azimuth Angle.   LHA < 180 deg. Zn = 360 - Az
Southern Lat.  LHA > 180 deg. Zn = 180 deg. - Az.   LHA< 180 deg. Zn = 180 + Az

Randall F Morrow PT
Kern County - Bakersfield

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