A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2019 Nov 10, 11:18 -0800
Mike freeman you wrote:
Although I am unable to confirm this online I assume the Calculated Altitudes (Hc) in Sight Reduction Tables are True Altitude.
So long as you accept that Hc is for a particular body, at a particular time and place, then yes Hc is the True Altitude.
On most occasions, we're not quite at that place, and that's the background behind the intercept method of plotting position lines.
If we've pre-calculated, Hc for a particular time, and our observation is early or late, then we must make a correction for the motion of the body (MOB), but this can be done at the plotting stage.
Also, if the tables are produced to cover a large number of years, then we might have to make a small correction for precession and nutation, but this too can be done at the plotting stage. DaveP