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Re: Amplitudes
From: Jeremy C
Date: 2010 Jun 3, 20:31 EDT
From: Jeremy C
Date: 2010 Jun 3, 20:31 EDT
JK wrote:
===========
the value of introducing the "amplitude" concept -- it seems
completely unnecessary. What's wrong with Zn?
-==============
These days with calculators and computers there is no reason to shoot
amplitudes unless you want to. If you are using strictly tables it is
easier for two reasons right off the top of my head:
1) relatively time insensitive
2) much easier to do a simple interpolation of 1 table than a triple
interpolation of HO 229 or equiv.
The latter reason is why in school we always looked to grab an AM
amplitude of the sun to avoid having to do the lengthy calculation of an AM
azimuth later in the morning.
An another topic, i wonder why Bowditch, in most editions I've read,
has always used the 1/3 of the sun's diameter as the rule of thumb rather than
the semi-diameter. Perhaps Byron can shed some light on this since he
knows Mr. Brown.
As Greg calculated, the dip differences seem fairly small considering
the accuracy of most of the instruments we are apt to use. I suspect that
my errors lie more with the inconsistent refraction than anything else.
Also remember that I am mostly shooting in the tropics so there is little change
in Zn in the time it takes for the sun to change altitudes between even zero and
semi-diameter above the visible horizon. If I were making for the English
Channel things would be different.
As far as tools, I tend to use a 6x Alidade for both Azimuth and
Altitude, so I am fairly confident of my bearing lines to about 0.25
degrees. Azimuth circles I will not be certain better than 1/2 a degree
due to the width of the "bar of light" that it produces on the compass
card.
I also did the Franklin technique and compared it to my azimuths and came
up with the same result, so I am fairly confident with my results near land in
either case. I posted these experiments a few weeks ago.
Jeremy
