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I wrote earlier:
"Why do you care to "call noon" at all?  This is one of those navigational
traditions on commercial vessels (specifically) that people love very much
but its navigational significance is hard to fathom."

Jeremy, you answered:
"I am not sure of this question. [etc.]"

Yeah, I wasn't quite sure how to ask it, but your answer gave me enough
information, I think, to understand how this usage connects with older
tradition. When you say that you "call noon" you're referring ONLY to that
moment when you perceive that the Sun has begun to descend. You're all well
aware that is some time quite distinct from actual "local apparent noon" but
by tradition you "call noon" at that point in the sense that this is when
you will stop looking and read off the best altitude. See, historically,
they did something else with that call of noon. They set the ship's clocks
to 1200. Today, on commercial vessels, you set the clocks to the best local
time zone. So the time aboard ship is GMT +/- some integral number of hours
chosen in such a way that it's usually not more than half an hour from local
mean time. This is the time by which work and meals and so on are scheduled
aboard ship (as distinct from the time used in navigational calculations).
When you "call noon" today, you could as easily say "mark" or "Sun
descending" or something else, but you're continuing a long tradition by
using that time-based expression.

And you asked:
"My question to you Frank, and anyone else who cares to answer, is what
methods do you use to observe LAN?  I am certainly open to better
techniques."

First, so there's no misunderstanding, I have never done celestial sights
any more than a dozen miles from land. I do navigation education and
history. And I don't have the slightest complaint with the way you do the
LAN sight. Sounds quite normal to me! I was merely curious about the
terminology you use. May I ask, where did you study celestial first? Did you
go to one of the maritime academies? Also, you clearly do lots of celestial
sights on your vessel. That's unusual these days. I'm sure you do many of
them for your own satisfaction and pleasure. Is it also because your captain
is a fan of celestial?

And you wrote:
"Of course in this day in age, it would be better for me to note my GPS
longitude, punch it into my computer, get time of LAN, and then shoot it at
the exact time to get a more accurate position, even underway."

Yeah, and if you've already looked at the GPS output, why shoot the Sun at
all (except for pleasure and practice, of course)?

And:
"The reason it is still practiced, is that at least in the US, the  US Coast
Guard requires all mates to be tested on this material and even have a
practical assessment done (ie go out and shoot a LAN) in order to obtain
certain ocean licenses."

Do you happen to know which USCG licenses still have a celestial
requirement? The situation today reminds me in many ways of the situation
with respect to "lunars" in the year 1900. Some licenses required them, but
they were almost never used at sea except by enthusiasts.

And you wrote:
"Historically LAN was shot because it was fairly  independent of an exact
time piece.  LAN was usually advanced or  retarded and crossed with an AM
sunline advanced to noon."

Yes indeed. Well into the middle of the 20th century, on many commercial
vessels, even LOPs were dispensed with. Time sights gave longitude and LAN
gave latitude. Navigators usually understood that these could be treated as
LOP sights but it was the tradition to do a pure longitude sight (a time
sight) and a pure latitude sight (a meridian Sun sight).

You wrote:
"Let's see if my math is correct:
The sun is on the meridian at 16h 44m 25s
The max HC (70d 09.4') occurs between 16h 43m 30s and 16h 45m 27s at the
given latitude.  During this time declination changed less the 0.1 minutes
of arc.  However, since we are steaming south, the sun will continue to
rise due to the change in latitude and will peak around 16h 46m at 70d
09.6.  The sun will have descended 0.2 minutes of arc by 16h 47m 00s."

I haven't checked your math, but I have no doubt that you've got it right.
And that fits with my understanding of your use of the phrase "call noon"
above. You 'call noon' at max altitude (or shortly after) even though it is
not "literally" noon.

And you wrote:
"Spending a half hour of time shooting a large number of sights to obtain  a
latitude LOP so that the error is less then a pencil line on a plotting
sheet while the captain is breathing down my neck for the noon slip is
certainly "horribly impractical" to me."

Why don't you just use the GPS then?

"On a sailboat it might  be different."

Sure. It all depends on the circumstances. But I think I should clarify that
the purpose of taking a series of sights over 30 or 40 minutes is NOT
necessarily to get a perfect latitude LOP but rather to get latitude and
longitude simultaneously with only a small amount of calculational effort.
You take a series of altitudes, correct them for the distance run and the
changing declination of the Sun, and then plot them on graph paper. The peak
altitude is worked up as a normal LAN sight (even if you missed the exact
time of max altitude, you can get it by graphing). The corresponding time,
at the axis of symmetry of the parabola through the points, corrected for
equation of time, immediately yields a longitude. This is a procedure that
is very easy to teach and requires no sight reduction tables. The resulting
longitude is typically about five times worse than the corresponding
latitude.

You added:
"Exactly, and since even a "slow" ship is traveling in some
direction(usually changing both latitude and longitude) at 13 knots, and in
my case 18  knots 0.3 nm of latitude per minute on N/S tracks), the math
involved to correct each of 20 or so sights over 20-30 minutes would require
quite a program to correct the changes of latitude and Ho due to the varying
position of  the ship at each sight."

Not, it really doesn't require anything complicated at all. The correction
of the altitudes for the vessel's motion and the Sun's changing declination
is not hard at all. There are many simple ways to do this. If you have the
chance sometime, you might get a kick out of a little navigation manual
called "Latitude & Longitude by the Noon Sight" written by Hewitt Schlereth,
published in 1982. He had his own particular method for applying the
corrections. It was a very simple, easy means of navigating a vessel. I'm
not recommending this book as a must-have or the best approach to analyzing
this set of sights, but it's nice to see that someone put it down on paper.

Jeremy, you also wrote:
"The time  spent taking that many sights added to data entry and plotting
would make a star fix look like child's play."

Now I'm certain that you've never tried it out. The method is FAR EASIER
than a star fix. But the time involved actually taking sights is definitely
an issue. If you're never able to take twelve Sun sights over forty minutes,
then you can't do it. Of course, what are you doing wasting time on Sun
sights in the first place? You do celestial for fun, right? Your position
comes from GPS.

"As an aside Frank, I see that you are in Groton, CT."

Sort of! I'm in Chicago. That's my primary residence, but I have worked at
the Planetarium at Mystic Seaport several times (Mystic Seaport is
technically in Stonington, CT but that's literally a stone's throw from
Groton, CT), most recently in 2002-2003. I'm in Connecticut quite often
though.

"I live in Cutchogue, NY; about half the way up the North Fork of LI.  It's
too bad the conference in Mystic isn't a month later, or I'd  be attending.
I do hope you do such meetings in the future as I'd like to  talk shop."

Cutchogue, eh? Very nice. Yeah, it would be great to sit down and talk shop.
I'm sorry you can't join us next month. I will probably be in Connecticut
again later this summer. I'll let you know my schedule. It's a short ferry
ride from the North Fork to New London. I would be happy to show you around
Mystic Seaport and introduce you to Don T.; he's been teaching celestial
navigation there for nearly forty years.

 -FER



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