NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunar Distance Puzzle
From: UNK
Date: 2011 Aug 21, 16:59 +0000
From: UNK
Date: 2011 Aug 21, 16:59 +0000
On 2011-08-21 15:25, George B wrote: > The primary contribution to the distance correction is lunar parallax, > and as Dave showed in a refraction-free world the problem is still > solvable. Where has Dave shown that? It actually cannot be shown. > Finally as to Frank's comment that the third lunar distance in the > problem can't contribute additional information it can only confirm > the previous two... With one lunar distance and one equation you have > to input values for two of the variables, namely the two altitudes (or > lat and long), in order to get GMT. With two distance measurements you > can input GMT and solve the two equations for lat and long, i.e. find > out where the LOPs intersect. > > It is important to note that with two distance measurements if you > input a different GMT the LOP intersection will shift to a different > lat and long. So the role of the third lunar distance measurement will > basically be to pin down GMT to the correct value. Of course all three > equations contribute to finding all three unknown variables, it's not > like we can say one of them determines GMT etc. Adding a fourth > measurement would not provide any new information, but would > over-constrain the problem and allow one to calculate a goodness of > fit chisq. > Amy, Bob and Jim have together 15 candies. Amy and Bob together have 9. Can you tell me how many candies each child has? Oops, you need a third equation. Jim has 6. Can you tell me now? Herbert