"Wayne.B" wrote in message
...
On Sun, 20 Apr 2008 16:22:29 -0700, "Capt. JG"
wrote:

Yes, you can get an LOP with the information/equipment I supplied. I
didn't
make this up, wish I did, but it works.

Well please enlighten us. Heavenly bodies still hold a certain appeal
in these days of push button navigation.

They do for me as well, although I'm not familiar with more than the basics.

I'd be happy to, but just to be clear, I didn't come up with this, and I
haven't tried it. It seems to be logically correct, and I'd like to try. If
you have a sextant, and you want to try it, I'd love to hear the result.
When I get one, I'm definitely going to give it a try. Courtesy of a
Celestaire handout at a seminar I attended. No mention was made of accuracy,
which I would think is dependent upon the adjustment of the various
instruments (sextant, compass, watch), as well as the observer.

Most of you are familiar with the stroboscopic effect. That's why the
flashing light makes the dancers seem to be frozen, or at least to have
jerky movements. We check the timing of motors with a flashing strobe, which
makes the rotating timing marks seem to stand still. You can do the same
thing with the stars.

Stars move through the sky so regularly that every 23 hours 56 minutes and 4
seconds, each star is back in the same place as the night before. This means
that if you laid on the ground facing up, and every 23h 56m 4s you opened
your eyes for a moment, the stars would appear to be stationary in space,
always in the same place. If you took a round of sextant readings on any of
the stars you cared to keep track of (you can give them any names you wish),
the readings would be the same night after night, as long as you did it
every 23h 56m 4s instead of every 24 hours. The readings would remain the
same - unless you moved! If you move between the readings, your movement
will be reflected in changed readings - one minute of arc for every mile you
moved.

If a star's reading increases by 23' for example, then you must have moved
23 miles in its direction. If you have a compass with you when taking
readings, you will know what direction to plot the new line of position. You
simply plot a line from your previous position in the direction of the star,
measure 23 miles (the intercept) and plot a line perpendicular at this
point. This is your new LOP. If you do the same for several other stars, you
have a new fix.

The advantage of this method is that it is incredibly easy to do. You don't
even have to correct for refraction or dip. Even if your sextant has an
error, it won't matter.

The disadvantage is that each position depends upon the previous one, so
that small errors may build up to be large ones. If you are on a long
voyage, you may find that the original stars are no longer visible at a time
when they are useful. Before this happens, you will need to pick some new
stars, and take a double round of sights - one for the fix, and one to
establish a basis with the new stars.

--
"j" ganz @@
www.sailnow.com