NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Were Short methods really Short?
From: Stan K
Date: 2016 Aug 7, 20:03 -0400
From: Stan K
Date: 2016 Aug 7, 20:03 -0400
David,
I just confirmed that, for your example, the azimuth of the sun when its upper limb is on the visible horizon is 62.2569...º, rounding to 62.3º. The azimuth of the sun when its center is on the visible horizon is 62.0937...º. rounding to 62.1º.
Another thing I failed to mention is that you used the closest latitude and declination available in Table 27. Had you interpolated both you would have gotten 28.56038º. The Table 28 correction is -0.7º.
Using the rounded values (might as well, since Table 28 values are rounded): 62.3 + 28.6 - 0.7 = 90.2º, much closer to 90º than 28° 36' + 62°18' = 90º54' or 90.9º. (Using the unrounded values results in something closer to 90.1º, even better.)
Does this work for you?
Stan
-----Original Message-----
From: slk1000 <slk1000@aol.com>
To: NavList <NavList@fer3.com>
Cc: slk1000 <slk1000@aol.com>
Sent: Sun, Aug 7, 2016 7:12 pm
Subject: Re: [NavList] Re: Were Short methods really Short?
From: slk1000 <slk1000@aol.com>
To: NavList <NavList@fer3.com>
Cc: slk1000 <slk1000@aol.com>
Sent: Sun, Aug 7, 2016 7:12 pm
Subject: Re: [NavList] Re: Were Short methods really Short?
David,
I've been out of touch for the last few days. I just got back and saw your message. Without working through the numbers, which I will probably do later today, a few things come to mind:
The app that give the sun's azimuth at sunrise probably gives the azimuth when the upper limb is on the visible horizon. Bowditch Table 27 give the azimuth of the sun when its center is on the celestial horizon. (Table 28 is used to correct this to the visible horizon.)
I suspect that these considerations might account for the discrepancies.
Stan
-----Original Message-----
From: David C <NoReply_DavidC@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Fri, Aug 5, 2016 10:24 pm
Subject: [NavList] Re: Were Short methods really Short?
From: David C <NoReply_DavidC@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Fri, Aug 5, 2016 10:24 pm
Subject: [NavList] Re: Were Short methods really Short?
The work sheet for Ageton Classic has entries for Prime Vertical calculations. The second of the calculations uses the formula for amplitude at rising
sin A = sin d * sec L.
sin A = sin d * sec L.
The worksheet (incorrectly I believe) describes the result as Z.
On 17 July 2016 when L = S41° 06.5' and d = N21° 08.6' Ageton Classic gives Z=28° 36'. An app gives the sun's azimuth at rising as 62.3° or 62° 18'.
28° 36' + 62° 18' = approx 90°. Why the result is not exactly 90° is probably a thread in itself (unless I have made an error in my calclations).
As a check, for Lat 41° and Dec 21° Table 27 in Bowditch gives amplitude = 28.3° or 28° 18'.
