Are you into History - well, Im not, except about certain things that interest me.  I couldnt care less about the history of corsets, electronic computers, the internet, or Greenpeace.  Nor do I fondle books of farming, dentistry, book-keeping, or knitting.  However, nautical history (outside of war statistics) tickles me pink, as well as a few other subjects of historical interest; such as the history of the paper-clip.

Last night I began to read A HISTORY OF NAUTICAL ASTRONOMY, by Charles H Cotter, 1968.  I only made it to page 24 before I fell asleep, but I found myself still thinking about what I read as I awoke this morning.  The book starts with the Babylonians and Phoenicians in easily digestible morsels, then continues on with science, instrumentation, and methodology from a historical perspective (from the contents page). The author is English or Scottish which makes the book a bit dry, so to compensate I just imagine the reader in my head has an English accent and the reading goes well.

I think it will be such a good read that I thought to tell you about it now so that if any of you decide to read the book as well, we can discuss it here in the forum.  Anyway, the book is free as a download at my favorite library website - Survivor Library.  Here is the book pdf (the download is automatic).  I found it in the Astronomy section.

There are hundreds of other titles in a few dozen categories there at the SL.  Take a look; if history isnt for you there are plenty of other enticing subjects to wet your whistle. By the way, I was just teasing about the paper-clip.

joe

Gentlemen,

In a pretty routine calculation I faced a problem which forced me to redo that calc three times. Let me explain myself:

Three sighting of Sun and three sightings of Moon. Regular fix. Supposed to be.  Except one nuance: The lat is a whole number  of degrees and 30 minutes. No problem.  The question is what App.Lat. to select: 30 minutes less or 30 minutes greater to get a whole number for the entry into Pub.229. Getting suspicious results in both attempts I decided to interpolate data for Hc and Z between two neighboring Lats. Then the fix appeared to make sense.

I checked the difference between Hc  in adjoining columns.  The delta is APPROXIMATELY the same.

The bottom line: I just like to share this small occurence.  Am sure that most of you are familiar with this issue and have no problems.  But anyway, decided to share it.

By the way,  I understand that there is no direct proportionality between data in Pub.229, because all of it are solutions of navigational triangle using spherical trigs.

Thank you

I went to the mall the other day then decided to spend some time watching boat traffic at the nearby dock (if you can really call it that).  There was a large barge, about 250 feet long, offloading sand by the truckload.  The dump Trucks drove aboard a front ramp where a loader scooped the dirty stuff into them.  They started at the bow and were working their way aft when I noted something weird... she was shipping water - the stern was awash.   There were perhaps three olympic pool sized piles of sand to be removed, and as the tide continued to fall I noted that the bow had not settled; she was aground... bottomed out.  However, the stern was still afloat and settling with the tide.  I was told the captain was in town shopping as mariners with worried faces scampered around the vessel trying to evaluate the predicament.  I dont know what finally happened because I had to leave for home, but I assume she's ok... I have not heard anything in the news.   If the channel was much deeper than where the bow stood Im sure they needed the pumps.  They told me the captain was under 30 years old - and probably a relative of the owner; that's the only way these nincompoops get the good jobs- you have to know someone... a competent captain would cost too much for these greedy boat owners. In unfamiliar waters a competent captain would have stayed with his ship instead of shopping ashore for a massage parlor.

We all have seen the nice moon HP tables provided by NAUTICAL ALMANAC website, but I wonder if you know that there are two versions... the second of which I can't make heads or tails.

The copy of the Almanac moon HP table - the one with separate lists for upper and lower limbs - makes good sense once you get used to it.  However, there is another version tacked on the end of the Sun/Star/planet increment download that boggles the mind.  Not only are the numbers incomparable with the Almanac HP table, but there are no upper and lower HP divisions - only a single number.  That single number does not compare to UL or LL corrections noted in the Almanac version. 

On the same page with the errant HP table is a Refraction table that I like to use with Gunter shots, and the DIP table seems sound, but that HP table gives me the willies...  Until someone can tell me how to use it so the numbers match the Almanac version Im not going near it.

joe

Anyone who has read Table 4 instructions will agree that they are most confusing... I think I know why - there is an error in the document.

Here is the problem:  Read along if you have table 4 instructions handy.

OT = Jan. 18d 04h - 7h = Jan. 17d 21h.    (so far so good)

Main Table, Jan. 17d OT, E 2 33 (- 5)          Dec. S 20 51 (- 12)    (still good)
Table b for 20h OT             - 4                             - 11             (PROBLEM)

AH- here is the problem; the 20 should read 21 as per the OT line above.  If the OT was in fact 20, the DEC correction -11 would change to -10)?

Jan.17d 20h OT, corrected E 2 29       (SAME PROBLEM)

Here again the 20 should read 21 as per the OT line above.

These small errors made my life a living hell as I tried to figure out from where they got the 20.....  

After realizing the error and a few practice problems I compared the GHA and DEC with an Almanac, I noted only a small difference between the two; less than a minute.  That's not too bad for a few sheets of paper good for almost two score years of Sun GHA and DEC data.

joe

OK, so Im not a big TV fan.  I have not watched TV in many years, but this is not to say i dont like movies. If provoked by a good title or reputation Ill force a DVD into the machine, make some pop-corn, open a cold bottle of soda, and immerse myself into a world designed by some obscure producer. 

A year ago or so I found a movie on the internet made just for me.  Ive probably watched the goofy thing 20 times and I keep going back for more.  The acting is superb, the set is vivid and appropriate, the special effects are adequate, and the music score is pleasant. 

The Movie LONGITUDE  has been my favorite for quite some time now and has displaced THOSE MAGNIFICENT MEN IN THEIR FLYING MACHINES (another wonderful British film) as my go-to video for perennial entertainment. 

LONGITUDE is quite a long movie and seldom, in my view, slows down.  My only weak criticism would be of the actor who plays John Harrison's  son - the eldest. (there are two actors playing the part).  The one who plays the son as an adult is a bit of a ham. Several times he comes close to spoiling what might be one of the greatest made-for-TV movies ever created...  Another great British movie  is called THREE MEN IN A BOAT. 

Watch LONGITUDE on Youtube soon - you wont regret it.  There are several copies of this movie on the internet - I think Ive given you the best one. Its in two parts so when you see the credits half way through dont freak out... the second half of the movie starts almost immediately.

Joe

I have a dilemma... two great looking sextants at good prices (about $250); I don't know which to choose.

The Freiberger Sextant has a lightweight aluminum alloy frame, a 4 x 40mm scope, a wooden storage case with instruction manual.  The horizon mirror is serviceable but needs replacing.
 
The Tamaya 833 has a 7x35 scope and is in good shape, no storage case.

They both appeal to me.

Which is the better sextant?

joe

I am confused as to why there is HP data posted on the daily pages for venus and mars.

If and when, would be my question, do we use this correction???

joe

What exactly is table 5 used for???

Perhaps this subject has arisen before, however it might shed an interesting light on choice.

Given the fact that in this day and age we have the absolute best navigation tools ever devised, we, as purest CN lunatics, long for technology of bygone days -  nevertheless we still welcome the chronometer as a standard piece of gear. 

Granted the chronometer greatly  improved the accuracy of early navigators, Slocum - unable to afford one - used an old tin clock.  So how did he navigate? There was no WWV or radio beacons, etc.  The answer - The lunar method.  He didnt need a chronometer, and although a goat ate his charts, he made the trip without much difficulty.  Of course the lunar method is more cumbersome mathematically than our present day single shot table methods, but he still needed a sextant - and circle the globe he did.  HOW COOL IS THAT?  I once (ignorantly) used nothing more than a road map to navigate the great Yukon River in Canada by canoe.  The HMS Bounty captain, after mutiny, had but a very limited supply of NAV tools to usher his surviving crew thousands of miles to safety - avoiding known islands of inhospitable natives - without chart table or enclosure within to work.

My question for you:  What is the absolute minimum navigational equipment list and navigation technique you might feel comfortable with if circumnavigating the earth solo or with a minimal crew?  (include any and all paper references, tools, recording implements (pencils etc.), space requirements, support equipment (table, chart room, etc), and lighting. Exclude supplemental emergency devices or implements.  

Have fun

joe