A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2009 Jul 24, 11:53 -0400
Hi Hanno Ix
See my answers interspaced below
Suppose your celestial body is the sun. If reducing for a meridian crossing (sun on your line of longitude), then the hour angle T is 0 (less than 1 degree). As a practical matter, the Bygrave is quite compressed under 5 degrees for the LogCosine scale, so reductions when the sun is close to your meridian suffer from accuracy issues.
If reducing when the sun is directly east or west of you, when the hour angle is 90 degrees (sunrise, sunset) similar issues result.
Just use the standard azimuth and altitude equations that can be directly reduced using a calculator.
Depends upon who you talk to. Due to cost, we probably won’t be looking at historical replicas.
HO229 offers accuracies to 0.1 arc-minutes, about 10-20X the accuracy of the Bygrave. It is heavier, larger and requires tabular lookup instead of slide rule manipulation.
Others will have different preferences for tabular reduction or for computer aided reduction. The beauty of the Bygrave is the small size, small weight
and rapidity of reduction
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