NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Difference between HO 249 and USNO website
From: Gary LaPook
Date: 2016 May 17, 17:06 +0000
From: John Almberg <NoReply_Almberg@fer3.com>
To: garylapook@pacbell.net
Sent: Tuesday, May 17, 2016 9:53 AM
Subject: [NavList] Difference between HO 249 and USNO website
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From: Gary LaPook
Date: 2016 May 17, 17:06 +0000
It appears that your problem is that you used different assumed positions for tach computation. Look at your input data to the USNO website, it is different than the AP shown in block 6 of the 249 reduction. When you do that you find the Hc is 21-22.6.
gl
From: John Almberg <NoReply_Almberg@fer3.com>
To: garylapook@pacbell.net
Sent: Tuesday, May 17, 2016 9:53 AM
Subject: [NavList] Difference between HO 249 and USNO website
Hi there. I am wondering why the sight reduction results from HO 249 and the USNO website (http://aa.usno.navy.mil/data/docs/celnavtable.php) differ so much.
I've attached my own calculations using HO 249, and the results from the website. The Zn value is the same, but the Hc values are significantly different. Is this normal? Or am I doing something wrong (the most likely scenario!)
I should mention that I took the sight using a homemade 'astrolabe', so in my own calculations I am including no altitude corrections. i.e., no dip and no SD correction.
Any thoughts, much appreciated.
-- John
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