"thunder" wrote in message
news
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.

No contradiction. Only misconceptions in your mind. Let me explain one
more time. This time please get your head out of your ass.

1) Astronomers plotted celestial bodies and made tables telling where
these bodies would be in the sky and when.

2) a sextant and tables of celestial body positions can be used to tell
you your geographical position on the face of the Earth.

3) the TABLES don't work without accurate time because the angles change
as time changes. A second of time matters. This is because the Earth
rotates.

4) The lat/lon grid system is an arbitrary one. It is based on the
properties of a sphere and has NOTHING to do with time. Time could stop
but the grid system would remain exactly the same. Picture actual lines
painted on the Earth's surface. These lines remain even if time stops.
Time has NOTHING to do with the grid system

5) Time IS USED to reference the exact angle of a celestial body as it
appears from a given GP on the face of the sphere which GP is defined by
the lat/lon grid.

Longitude is NOT based upon a revolving Earth. Longitude lines exist as
an artificial series of lines space on the Earth's surface by geometric
parameters. Time is not involved one iota. The Earth could stop rotating
yet the Meridians of Longitude would still exist.

Wilbur Hubbard