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Re: Longhand Sight Reduction
From: Bruce J. Pennino
Date: 2014 Nov 17, 09:20 -0500

Hello Greg, Gary and Hanno and others,

Doniol sight reduction seems quite innovative......well done and most interesting. Now that you’ve posted a couple of examples, I’ll give the method a try (on some cold wintry evening). I usually use two methods whenever I do a reduction, just so I don’t get rusty in other methods.My recent favorite is still Weems 1927 LOP Book (1943 version) followed by H. O, 249 and hand calculator.

This past weekend , for the first time, I used my USN AH No. 8 ( a mercury AH with a triangular hood) for a noon latitude sight. The wind was really blowing but the mercury was so still. Even though I rushed through the sight, the sun was earlier than I anticipated, my result was within 1 minute of arc of my actual location.

I’ve compared results with Hg AH and my mirror AH ( using a cheap Empire torpedo level and ordinary mirror glass ) and my results are always within a couple/few of minutes of arc. One of these days I’ll use the first surface mirror and Hg AH.

Again, thanks for all of the work. Best wishes to all.

Bruce

From: Greg Rudzinski

Sent: Thursday, November 13, 2014 10:56 AM

To: bpennino.ce@charter.net

Subject: [NavList] Re: Longhand Sight Reduction

Gary,

To get you introduced see this link to my blog on the Doniol sight reduction method using sin, cosine, and haversine tables.

http://gregrudzinski.blogspot.com/2014/06/longhand-sight-reduction.html

Hanno Ix has modified the original formula so that just haversines are used thus only a single table is needed to derive the zenith distance. My contribution is the formating of the modified haversine Doniol formula into a 2 column reduction for practical use. There are three natural haversine look-ups for L+d,L-d,LHA and a natural arc haversine look-up for zenith distance. No logs are used. There is a single multiplication step done longhand. There are five summing steps.

d (A) (B)

L+d Hv Hv

L-d +Hv +P

1-sum Arc Hv sum

sum ZD

LHA * Hv Hc

L=latitude, d=declination, Hv=haversine, LHA= local hour angle (converted to meridian angle for LHA>180°), P=product, ZD=zenith distance, Hc=calculated altitude

Greg Rudzinski

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