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

S.Simon


"Wally" wrote in message ...
Jeff Morris wrote:

One sight at local noon yields your latitude and longitude.

Clearly not true - for starters, you can't take "one sight at local
noon" unless you already know your longitude. If Neal had actually
ever taken a Noon Sight, he would know this!

I am but a sweet, innocent, fresh-faced n00b, and wonder if my reasoning is
correct...

I have a sextant and an accurate chronometer set to GMT. I am somewhere on
the surface of the earth, but know not where. I awaken from my slumbers one
morning and find myself wondering what my longitude is, so I watch the sun's
upward climb across the sky. As it approaches zenith - local noon - I note
the time on my chronometer and then crunch time into degrees to determine my
longitude.


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

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

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

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

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.

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

To find longitude? If so, how's that done? I just put together a little
spreadsheet which seems to find longitude for zenith at any given GMT time.

06:00 gives -90 (90 deg east)
18:00 gives 90W
17:21:50 puts me very close to your meridian - 80d 27.5'W


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