On Sun, 11 Mar 2007 20:30:44 -0400, Wilbur Hubbard wrote:

Some recent comments by an elderly gentleman subscriber to
alt.sailing.asa got me to thinking. The comments indicated a marked lack
of understanding of celestial navigation. I thought I'd take a minute to
put to rest such misconceptions.

1) A grid was arbitrarily placed upon the surface of the Earth. This
grid consists of Meridians of Longitude and Parallels of Latitude. One
can state one's geographical position(GP) on the face of the earth as an
intersection of this grid system.

I'll admit to knowing very little about navigation, but I know enough to
realize the grid was not arbitrary.



2) The angle of various heavenly bodies was calculated with reference to
the Earthly grid system and expressed as angles from a given GP at a
given time.

3) Using a sextant one could accurately calculate the angle to a
heavenly body.

4) The tables show angles along various grid lines at various times.

5) In order to use celestial navigation one must have a sextant, tables
and an accurate time piece.

6) Meridians of longitude are not based upon time any more than
parallels of latitude are based upon time.

There seems to be a contradiction between 5 and 6. Longitude not based
on time, yet the need for an accurate timepiece? You seem to overlook
the obvious, both time, as we measure it, and longitude are based upon
the same thing, a revolving earth.

I hope this helps.

Wilbur Hubbard