Actually, I never used this method, except in an "emergency". The
normal method used, was to get a couple/few morning sunlines and do a
running fix by moving them up along the course line and crossing them
with the LAN sight.

otn

Thom Stewart wrote:
OTN,

Now, with your explanation, Neal may be able to get a Local Noon sight.
Maybe, I'm still not sure he aware of what we are talking about. Hitting
a high noon fix with the Earth traveling over 900 MPH is kind of like
catching a Fly with Chop Sticks.

OTN your method is the correct way to take a Noon Sight. Even the
instruction that came with Neal's (Also mine) Sextant explains the Noon
Sight that way.

Ole Thom

So, how do we split the point and assist? Or do we each get half a sack?

The funny thing is that every beginner plots a noon sight and has the moment of
realization that the Sun "hangs" at an essentially constant altitude for several
minutes. Clearly Neal has never done this. Its a perfect example of someone
that reads a book once but refuses to learn from anyone - its just like his
understanding of the rules.

--
-jeff
"Constant Vigilance!" - Frances W. Wright


"Thom Stewart" wrote in message
...
Right on Jeff,

You sprung the time trap on Longitude that I'd set up for Neal. It
didn't take you anytime at all. I raise my glass to you! You even picked
up the error of Mr Davis. They recommend using the plastic model for
practise only.

I'll only mention that a ten mile error is over the horizon and out of
sight. This in real voyaging could make DED course selection rather
iffy. I guess tied to a mooring overcomes that problem.

Good Job Jeff!

Ole Thom

For Longitude can't you just use an Analema? (This post was really an excuse to
use that word!)

Actually, a one page text version of the Analema will be accurate to about 10
seconds for any year. The declination of the Sun at meridian passage, needed
for Latitude, can also be found in a "one page perpetual" version, accurate to
about 12 arc-minutes with interpolation.

If anyone is interested in emergency traditional navigation, they should find
"Particularized Navigation, How to Prevent Navigational Emergencies" by Francis
W. Wright; its out of print but available from some sources. This includes a
small book on celestial, and even smaller pamphlet with tables, and even yet
smaller sheets for lifeboat navigation.


--
-jeff
"Constant Vigilance!" - Frances W. Wright


"otnmbrd" wrote in message
ink.net...
Wrong. You need the Almanac. For a noon sight, you need to know
declination to compute latitude. As for longitude, using the method you
are referring to, you need to convert LMT at time of sight ( reason for
error) to GMT, which you convert to GHA and then longitude. Again, if
you had a clue as to what you were talking about, you would realize that
this method was not all that accurate except in certain cases. LHA is
measured from you WEST, to the body. Go back to reading.

otn

Simple Simon wrote:
Sight Reduction Tables of course. I use HO249 for speed and simplicity.

You must have local hour angle because the sight is always a combination
of local hour angle and zenith. The tables help you to turn the local hour
angle into latitude since the sun moves daily because of the tilt of the
earth as the seasons progress.

S.Simon



"otnmbrd" wrote in message
ink.net...

Pleas explain which "tables" you are talking about and what
calculations you are making for sextant altitude and time. You sure you
want LHA?

otn

Simple Simon wrote:

That's it but you need tables. You need tables because you measure
zenith and local hour angle.

S.Simon

BG You'd need to define, as I haven't a clue as to what that is
(Analema).
When you get "into" the study of methods of navigation, you tend to find
many ways and "publications" that have been or are used for sights.
Personally, I still prefer (or did when I was using them) the older
tables (214?) for sight reduction.

otn

Jeff Morris wrote:
For Longitude can't you just use an Analema? (This post was really an excuse to
use that word!)

Actually, a one page text version of the Analema will be accurate to about 10
seconds for any year. The declination of the Sun at meridian passage, needed
for Latitude, can also be found in a "one page perpetual" version, accurate to
about 12 arc-minutes with interpolation.

If anyone is interested in emergency traditional navigation, they should find
"Particularized Navigation, How to Prevent Navigational Emergencies" by Francis
W. Wright; its out of print but available from some sources. This includes a
small book on celestial, and even smaller pamphlet with tables, and even yet
smaller sheets for lifeboat navigation.

Its the funny "figure 8" on the globe - it describes the "equation of time"

http://hpccsun.unl.edu/nebraska/analema.html

world's largest analema:
http://www.uwm.edu/~kahl/Images/Weat.../analemma.html

the equation of time:
http://www.astronomynotes.com/nakedeye/s9.htm

one page table that should be enough for Longitude:
http://home.netcom.com/~abraxas2/eot.htm



"otnmbrd" wrote in message
ink.net...
BG You'd need to define, as I haven't a clue as to what that is
(Analema).
When you get "into" the study of methods of navigation, you tend to find
many ways and "publications" that have been or are used for sights.
Personally, I still prefer (or did when I was using them) the older
tables (214?) for sight reduction.

otn

Jeff Morris wrote:
For Longitude can't you just use an Analema? (This post was really an
excuse to
use that word!)

Actually, a one page text version of the Analema will be accurate to about
10
seconds for any year. The declination of the Sun at meridian passage,
needed
for Latitude, can also be found in a "one page perpetual" version, accurate
to
about 12 arc-minutes with interpolation.

If anyone is interested in emergency traditional navigation, they should
find
"Particularized Navigation, How to Prevent Navigational Emergencies" by
Francis
W. Wright; its out of print but available from some sources. This includes
a
small book on celestial, and even smaller pamphlet with tables, and even yet
smaller sheets for lifeboat navigation.

Jeff Morris wrote:
Yes, its just that simple. You understand perfectly.

Good-o.


There's only
one problem. Here's what Bowditch has to say, from the 2002 edition
(LAN is Local Apparent Noon):

snip

Yup, I'm aware of the difficulty in taking a sight precisely at local noon
due to the sun apparently hanging in the sky, and that some method of
extrapolation from sights either side of zenith is needed.


The exercise of plotting a Noon Sight is one of the first things a
novice learns. Neal's lack of understanding shows he has never
actually done this.

Neal seems to be contending that it's possible to line up a limb of the sun
with the horizon, such that there's a perceptible difference between limb
and horizon being 'in contact' and being separated. While this may well be
possible when everything is nice and stable, I can't help feeling that it
would be rather difficult in a bobbing boat.


--
Wally
www.art-gallery.myby.co.uk
Latest work: The Langlois Bridge (after Van Gogh)

Thom Stewart wrote:

Read OTN's method of determine the Azimuth. You can't get a accurate
instant sight due to the speed of the earths rotation, Now, that
leaves the question; how accurate do you want to be? Your choice.
There are many way to get close but it's for you to decide. I like to
use a shadow facing true north & time but OTN's way is the exact way,
if your using your Sextant

I'll have a look at his post...


--
Wally
www.art-gallery.myby.co.uk
Latest work: The Langlois Bridge (after Van Gogh)

"Simple Simon" wrote in message ...
One sight at local noon yields your latitude and longitude.

How's about moon sightings?

www.webdigital.de/ cards/butts.jpg



S.Simon - has taken more noon sights than cherries!

"Wally" wrote in message
...
The exercise of plotting a Noon Sight is one of the first things a
novice learns. Neal's lack of understanding shows he has never
actually done this.

Neal seems to be contending that it's possible to line up a limb of the sun
with the horizon, such that there's a perceptible difference between limb
and horizon being 'in contact' and being separated. While this may well be
possible when everything is nice and stable, I can't help feeling that it
would be rather difficult in a bobbing boat.


Its really more difficult than that - as I said, the altitude of the Sun varies
less than 1 arc-second for roughly a minute before and after LAN; a few
arc-seconds for the minutes before and after that. The diameter of the Sun is
about 30 minutes, or 1800 arc-seconds, so we're talking a teeny, tiny, itsy,
bitsy amount here. If the Sun appears to be about the size of a pea at arm's
length, then this distance is about a tenth the thickness of a human hair (if my
napkin math is still good).

If that weren't enough, Neal claimed he just presets his sextant to the right
altitude, but even a good sextant can't be set better than about 12 arc-seconds,
most have errors much greater than that. Neal's plastic probably has completely
random errors more like 5 arc-minutes. And then there's things like the dip
correction, where a change in the height of the viewer of just a few inches
throws it off by more than an arc-second. On top of that, knowing the altitude
to preset means knowing one's Latitude - in this case to about 100 feet for each
arc-second. If my dead-reckoning were this good I wouldn't have need for a
sextant!

And remember, the Earth is moving 15 miles per minute (at the Equator) so there
isn't much room for error when making this determination. Neal claims he can
get 10 mile accuracy; its probably more like 100 miles with this method. In
reality, assuming Neal actually owns a sextant and has taken it out of the box,
what he has probably done is preset (as best he could) based on his GPS
position, and then verified that local noon occurred as predicted, within a few
minutes.

-jeff

Some of the older model sextants used half mirrors instead
of the modern see-through mirrors that make it possible to
have the sextant picture a sunset at LAN. The older
sextants were harder to use.

You being old and retired, I figured you'd probably have
some antique instruments.

S.Simon


"otnmbrd" wrote in message ink.net...

Actually, I never used this method, except in an "emergency". The
normal method used, was to get a couple/few morning sunlines and do a
running fix by moving them up along the course line and crossing them
with the LAN sight.

otn

Thom Stewart wrote:
OTN,

Now, with your explanation, Neal may be able to get a Local Noon sight.
Maybe, I'm still not sure he aware of what we are talking about. Hitting
a high noon fix with the Earth traveling over 900 MPH is kind of like
catching a Fly with Chop Sticks.

OTN your method is the correct way to take a Noon Sight. Even the
instruction that came with Neal's (Also mine) Sextant explains the Noon
Sight that way.

Ole Thom