|
|
|
|
|||||
|
||||||
From: David Weilacher (no email)
Date: Tue Aug 10 2004 - 12:35:17 EDT
What you have is pretty good.
You are trying to come up with the acute angle you would have got had you taken the sight against the normal horizon.
The only issue you might want to consider (although I wouldn't go for that degree of accuracy myself), is caused by refraction. If you look at the correction for semi-diameter and refraction, there is a small difference between lower and upper limb corrections. That difference is all about refraction at the top of the sun vs the bottom of the sun.
So, even though you are doing a lower limb reduction (I assume) and the arithmetic works the same (add semi-diameter), you may consider using the upper limb number for the correction.
This level of exactitude and complication should appeal to many on this list.
-----Original Message-----
From: Jim Thompson <>
Sent: Aug 10, 2004 6:50 AM
To:
Subject: Reducing back sights
Neither Dutton's nor Bowditch explain back sight reduction in sufficient
detail for me to be confident about the process. My understanding is this:
1. Raw altitude = back sight.
2. Corrected raw altitude: apply Index Correction and dip.
3. Corrected hs = 180d minus corrected raw altitude.
4. Then reduce the corrected hs as usual.
True, or bungled?
Jim Thompson
www.jimthompson.net
Outgoing mail scanned by Norton Antivirus
-----------------------------------------
Dave Weilacher
.US Coast Guard licensed captain
. #889968
.ASA instructor evaluator and celestial
. navigation instructor #990800
.IBM AS400 RPG contract programmer
|