A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding
From: Tony Oz
Date: 2018 Nov 7, 10:48 -0800
As I can imagine the life in a life raft - one has lots of time to watch the sky.
Assuming his watch is on UT - subtracting the UT of the sunrise from UT of the sunset one gets the daytime duration and also an estimation of the UT of apparent noon (by halving the interval). The latter immediately gives an estimate of his longitude: LHASun = GHASun + Lon, but at noon the LHA == 0°, so Lon == -GHASun as read from the watch.
But the problem remains: where to get the correct value of EoT for the day?