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Victor Garand wrote:
>
> In any case, it seems to me that the only legitimate introduction of GPS on
> this particular List is its use as a training aid (check) in developing
> proficiency in the area of celestial navigation.

There are other ways a GPS receiver can assist with traditional
navigation. For example, let's try a sight reduction. I've mentioned
that possibility on the list before, but didn't explain how to do it
in detail. So here goes.

Dead reckoning position is 25 51 N 069 25 W on 2005 Mar 17 1500Z. Load
that position into the receiver as waypoint DR1.

At that position we do a sextant sun shot. Ho = 52 39.

Almanac says Sun GHA = 42 55.6, dec = S 1 08.7. Load the Sun's
geographical position as waypoint GP1, using GHA as the west
longitude. (If GHA is greater than 180 the receiver will probably
reject it as a west longitude. In that case, convert to the equivalent
east longitude.)

Now use the receiver's route function to find the bearing and distance
from DR1 to GP1. My receiver says 132 T and 2232 miles. Convert the
latter to degrees and minutes (60 miles = 1 degree): 37 12. Hc is 90
degrees minus that angle, or 52 48.

The USNO online sight reduction calc says Zn = 132.5, Hc = 52 48.3.
Close enough!

Ho is 9 minutes less than Hc. If desired, that correction can be
applied to the DR position without any plotting: use the receiver's
waypoint projection feature to set a waypoint 9 miles from DR1 in the
opposite direction from the Sun. I get 25 57.0 N 069 32.4 W. Save that
as the estimated position.

   

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