|
Author
|
Topic: Z - Dec vs Dec - Z in Exercise 3.4 (7)
|
engsolnorm
|
posted May 31, 2006 09:25 AM
In exercise problem 3.4-7 I noticed an interesting thing.
Given a DR lat of 28-44 S, and
a Dec of 19-50.0, and
a Z of 47-30.3
The order in which the subtraction is performed yields different results...i.e.,
Z - dec = 47-30.3 - 19-50.0 = Lat = 27-40.3, which agrees with the DR, kinda...implies a 3.7 nm error.
But..
if we do this...
dec - Z = 19-50.0 - 47-30.3 = Lat = (minus)28-19.7
since the answer is minus, can we take this to mean a Lat South? If so, the DR error is now about 24.3 miles in error.
Which is correct?
Thanks,
Norm
From: Oregon
|
|
David Burch
|
posted May 31, 2006 09:53 AM
Hs = 42° 51.2' - 1.5' (IC) -2.9' (dip) = Ha = 42° 46.8 - 16.8' (upper limb alt cor) = Ho = 42° 30.0'
z= 90° - Ho = 47° 30.0'
dec = 19° 50.0'
lat = Ho - dec = 28° 40.0' which agrees with answer in the notes.
As for north or south, i would use the DR as the gage of that and not rely on specific subtraction rules.
note the valuale rule we have some where in the notes...
To find Lat from Lan, take the sum of z and dec, and if that is nonsense, take the difference.
That will generally work. exceptions are outlined in the notes.
concerning the subtraction, i would guess that the difference btween two angles is the same except for sign when you change the order of subtraction. maybe be a typo in the example you gave or a math error.
From: Starpath, Seattle, WA
|
|
|
