NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: UNK
Date: 2013 Sep 18, 01:17 -0700
Stan,
The EoT is given to the second and can thus be expected to be accurate to 0.5 seconds at tabulated epochs. The GHA values for the sun may have a bias of up to 0.15' of arc, which when compounded with the possible rounding error of 0.05' corresponds to a maximum error in EoT of 0.8 seconds.
It is true that the EoT continuously changes throughout the day. (Note that the bias of the tabulated GHA values grows and shrinks in tandem with the magnitude of this change.) The change between two subsequent table entries for EoT is never larger than 15s. The required interpolation is easy enough to be performed mentally. It is also insensitive to an error in the DR longitude as long as this error is smaller than a few degrees. I cannot see how introducing the GHA from the N.A. into the computation would increase the accuracy of the EoT so obtained.
On the other hand, it is easy to show that the tabulated GHA sun in the almanac may be improved by restoring it from the EoT on the same page. Try 2013-01-01T00 or 2013-01-01T12. You will find a difference of 0.2' in both cases, which can be explained as the intended bias plus the maximum rounding error.
Herbert
----------------------------------------------------------------
NavList message boards and member settings: www.fer3.com/NavList
Members may optionally receive posts by email.
To cancel email delivery, send a message to NoMail[at]fer3.com
----------------------------------------------------------------
