This has been up for a while.

Here's how to perform a star sight reduction using Pub. 249 Vol. 1

Go here- Methods  and scroll down to find this;

Complete Star Sight reduction Procedure

Based on Pub. No. 249 Vol. 1

Complete and thorough step-
by-step instructions for performing a
star sight reduction based on Pub. No. 249 Vol. 1 (aka- Ho-249)
Perfect for beginners using an AH

We thought it might be interesting to add a portion of the forum to the discussion of marine weather.  It doesn't have much to do with celestial navigation but we do, hopefully, all utter the phrase, "clear skies".

How many of you like to predict the wx yourself using your own instruments?

Or, if you do use services or programs, which ones are you accustomed to?

Are you often correct in weather prediction?

We don't want to lug around more paper than necessary.

For celnav work what have you found to be the minimum amount of paper or documents you need with you to carry out a sight reduction and plot?

For me it's-

- Altitude Correction Tables

- TABLE 4. - GHA and Declination of the Sun for the Years 2001 to 2036- Argument “Orbit Time”

- TABLE 4 — GHA ♈ FOR THE YEARS 2011 - 2019

- Increments & Corrections- Sun only on 2 pages

- Increments & Corrections for Sun, Planets, Aries, Moon (the "yellow pages")

- Table 5- Correction to Tabulated Altitude for Minutes of Declination

- Conversion of Arc to Time

- USNO's Navigational Star Chart

Finally- Pub.No. 249 Vol. 1 (stars) Vol. 2 or Vol. 3 - Latitude pages printed out for where I'm sailing.  I don't own any of the volumes.

   
Thought you would enjoy seeing a Lego mini-figure sailor with his sextant.  And you thought the Bris mini-sextant is small.

I happened upon an interesting book, Maps of The Ancient Sea Kings by Charles H.Hapgood.
The book discusses a chart made or compiled by Piri Reis in about 1513.  Though I'm no expert on the subject, the book does seem to require some faith as do books like "Chariots of the Gods".

Regardless, there's a good quote near the beginning of the book you might enjoy.  Navigators throughout history always get blamed for errors in position.

"A good description of the problem of finding position at sea is given by a 16th century writer quoted by Admiral Morison in his Admiral of the Ocean Sea:

"O how God in His omnipotence can have placed this subtle and so important art of navigation in wits so dull and hands so clumsy as those of these pilots! And to see them inquire, one of the other, 'how many degrees hath your honor found?' One says 'sixteen,' another 'a scant twenty' and another 'thirteen and a half.' Presently they ask, 'How doth your honor find himself with respect to the land?' One says, I find myself forty leagues from land,' another 'I say 150,' another says 'I find myself this morning 92 leagues away.' And be it three or three hundred nobody agrees with anybody else, or with the truth." 

Morison, Samuel E. Admiral of the Ocean Sea. Boston: Little, Brown, 1942 pages:321-322)

CelNav57

With a little effort you can get the Sun's GHA & Declination using TABLE 4. - GHA and Declination of the Sun for the Years 2001 to 2036- Argument “Orbit Time”. 

It's printed on one sheet of paper.


Our site also has The Nautical Almanac for the Sun only which has 15 days of the Sun's GHA and Declination on each page. Any year, printed on both sides, takes up about 14 pages.

The Nautical Almanac is necessary for the determination of GHA and declination of the various celestial bodies a navigator works with.

However, TABLE 4 is very difficult to understand and the explanation provided on the second page of the TABLE is confusing.

We wrote our explanation with the expressed purpose of making TABLE 4 easy to understand and use.  Of course, it does take some practice.


Hopefully, you'll find our explanation and examples useful.


How to use- TABLE 4- GHA and Declination of the Sun for the Years 2001 to 2036- Argument “Orbit Time”

Here's a nice video in which the sailor is using a sextant. 

It's his sailing trip across South Pacific, from Chile to New Zealand


Sailing for the Sun, video


Hope you like it.

CelNav57

You can determine GHA, closely, of an integral hour by taking the EoT (Equation of Time) and converting it to an angle and then subtracting or adding it to the GMT integral hour (converted to an angle).  Whether you add or subtract the EoT is determined by the time of Mer. Pass listed next to the EoT on each of Sun & Moon pages of The Nautical Almanac.

The bottom of The Nautical Almanac Sun and Moon page has the Equation of Time for each day on the bottom right hand side of said pages.  To get a more accurate figure use an EoT that is closest to the present hour of GMT.

At most you'll be off by around 2 minutes of arc.  Not bad if you're 1,000 nm from land.

Do you have any other ideas about this?


Carlos

Just saw that TheNauticalAlmanac.com now has listed the procedure for how to perform a sight reduction using Ho 249/Pub No. 249.

Here it is- Star sight reduction Pub. No. 249 Vol. 1


Looks good.

Just got a Davis Mark 15 plastic sextant.  Did a few sun sights and found the LOPs to be acceptable.  Not as good at the Astra III-B but fair.

The index mirror is a 2nd surface mirror.

The nice thing about the Mark 15 is that it's small and you can carry it easily in the plastic case it comes with and you'll learn how to quickly adjust the sextant for IE, side error etc.  It's not solid in holding its adjustment.

Will post more results as time goes by.

CP