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post #1 of 22 Old 03-28-2010 Thread Starter
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Celestial Navigation: Nautical Almanac

Even in the days of GPS one should know to find your position by classic celestial navigation. Just in case my GPS fails. Finally, I had some time on my last vacation and got a great book for that: Starpath, Celestial Navigation from David Burch.

Then I got back home and access to my Sextant and my 2010 Nautical Almanac I wanted to see if I can find my position. But the Sight Reduction Table is different to the ones I have in my study material.

It doesn't show Hc, d and Z but A/H, B/P and Z1/Z2. I also miss the SAME and CONTRARY part.

Who has an idea what to do?
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post #2 of 22 Old 03-28-2010
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AFAIK, the Nautical Almanac provides celestial positions for the sun, moon, planet, and navigational stars. It does not include sight reduction tables. For these, you need a set of tables such as HO 214, 229, 249, etc. These are available for free download, as is the 2010 Nautical Almanac.

For the Noon Sight (latitude by meridian transit) you only need the Almanac. Here are the three cases:

Sight reduction tables are not required for these computations.

Case #1: When latitude and declination are of the same name, but latitude is greater than declination, use the formula:

Lat = (90̊ - Ho) + dec

Example: The DR latitude of a yacht at time of LAN is 40̊ N. The declination of the sun for that date and time is 20̊ 15.0' N. Since latitude and declination are both North (same name), but latitude is greater than declination, the above formula is used. Assuming the corrected sextant altitude (Ho) to be 69̊ 45', the solution is as follows:

Lat = (90̊ - 69̊ 45.0') + 20̊ 15.0'
and thus, Lat = (20̊ 15.0') + 20̊ 15.0' = 40̊ 30.0 North

Case #2: When latitude and declination are of the same name, but latitude is less than declination, use the formula:

Lat = dec - (90̊ - Ho)

Example: Assume the observer is in latitude 10̊ South and declination is 18̊ South. Since latitude and declination are of same name, but latitude is less than declination, formula #2 applies.

Case #3: When latitude and declination are of opposite names, use the formula:

Lat = (90̊ - Ho) - dec

Example: Assume the observer is in latitude 13̊ South and declination is 4̊ North. Since latitude and declination are of opposite names, formula #3 should be used to obtain observer's latitude.

Bill

Last edited by btrayfors; 03-28-2010 at 08:50 PM.
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post #3 of 22 Old 03-29-2010
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you might want to check out bruce bauer The Sextant Handbook,
its a great resource...

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post #4 of 22 Old 03-30-2010
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Quote:
Originally Posted by SeppSF View Post
But the Sight Reduction Table is different to the ones I have in my study material.
I think the nautical almanac has a simplified ("emergency") sight reduction table. I also recently found

Erik's Nautical Web Pages

To be handy.

Quote:
It doesn't show Hc, d and Z but A/H, B/P and Z1/Z2.
Not sure what A/H etc. are. Maybe A/H is GHA? The Nautical Almanac tables I'm familiar with show GHA and Dec for each body, plus some extra corrections for the moon.

Quote:
I also miss the SAME and CONTRARY part.
Two coordinates have the "same name" if they are both east or both west for longitude and hour angle, or if they are both north and both south for latitude and declination.

Quote:
Who has an idea what to do?
My life doesn't depend on celestial navigation and I don't feel like paying for the book. I use "The Online Nautical Almanac"

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post #5 of 22 Old 03-30-2010
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While that's a great book on sextant maintenance and such, it does nothing for you when it comes to navigating with a sextant.
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you might want to check out bruce bauer The Sextant Handbook,
its a great resource...

Amazon.com: The Sextant Handbook (9780070052192): Bruce Bauer: Books

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post #6 of 22 Old 04-03-2010
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You could have a look at software to give you the almanac and do the sight reduction calculations - see WinAstro Celestial Navigation Software - Home Page for example.
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post #7 of 22 Old 04-03-2010
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The Nautical Almanac Site Reduction Method is entirely different from HO 229, as is different from Ho 214 as is different from Ageton etc.

Dick
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post #8 of 22 Old 04-04-2010
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I'd also vote for software. Even if you don't want to RELY on it, you can use it as a fast reality check. If it disagrees with your hand reduction--you know there's a problem somewhere.

Used Palm IIIxe PDA, $25. John Manson's "Navigation" suite for the Palm, probably another $25. Great little combination and yes, it can be used on older and newer and fancier Palms as well.
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post #9 of 22 Old 04-09-2010 Thread Starter
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Navigation without electronics

Hello All,

Thanks for your great advice. Actually I'm trying to find my position without the use of any electronics. So the tip with HO249 was great. For anybody who is looking for either 249 or 229. Actually the Starpath book is using the HO249 tables, which are SIGHT REDUCTION TABLES FOR AIR NAVIGATION.

I got my 2010 almanac from Amazon. But its kind of from the UK Hydrographic Office. But the Sight Reduction Table are showing different values than the HO ones.

I'll check it out on the weekend. I will try to find this position:
N37.76579, W123.10245. No worries...I'll bring a GPS as well.
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post #10 of 22 Old 04-09-2010
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Quote:
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Actually I'm trying to find my position without the use of any electronics. So the tip with HO249 was great.
A noble goal. You know you can get a slide rule with trigonometric tables?

s/v Laelia - 1978 Pearson 365 ketch
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