# 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, 14:43 -0500
Randall,

In one version both lat and dec get signs, + for N, - for S.
In another version lat is always + and dec is - if lat and dec have different names (hemispheres), + if the names are the same.
Either way should give the same result.
You may have seen this on older vs. newer Power Squadrons sight reduction forms, the latter version being the newer.

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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