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Latitude by Polaris - Sailing Aphrodite - 07-26-2024
Hello All
My first post, time to dip my foot in the water.
I'm returning to Celestial Navigation after some decades. The Mary Blewitt book Celestial Navigation for Yachtsmen gave me nightmares for years and years!
Working my way through David Burch's Celestial Navigation: A Complete Home Study Guide and am struggling to find the Polaris (Pole Star) Tables he mentions there are three corrections a0, a1 and a2 (T-22 in the book). I've spotted a Polaris (Pole Star) Table 2024 A157 that uses a Q correction, then states that you need to add a figure for refraction.
Have things moved on since David's book or am I looking in the wrong places?
Thanks
Sandy
RE: Latitude by Polaris - EdCa - 07-26-2024
(07-26-2024, 04:52 PM)Sailing Aphrodite Wrote: Hello All
My first post, time to dip my foot in the water.
I'm returning to Celestial Navigation after some decades. The Mary Blewitt book Celestial Navigation for Yachtsmen gave me nightmares for years and years!
Working my way through David Burch's Celestial Navigation: A Complete Home Study Guide and am struggling to find the Polaris (Pole Star) Tables he mentions there are three corrections a0, a1 and a2 (T-22 in the book). I've spotted a Polaris (Pole Star) Table 2024 A157 that uses a Q correction, then states that you need to add a figure for refraction.
Have things moved on since David's book or am I looking in the wrong places?
Thanks
Sandy
Sandy,
You're doing fine. Make your life easy- TheNauticalAlmanac.com has what you need- both a form to determine latitude and the 2024 Polaris Q correction;
Determine Latitude using Polaris
Polaris- Correction for (Q) (2024)
All of the above can be found here- https://www.thenauticalalmanac.com/Methods.html
The a0, a1..etc....is fine and well but the Correction for Q is faster and easier.
Give it a try.
Ed
RE: Latitude by Polaris - Sailing Aphrodite - 07-26-2024
Thanks Ed.
I shall give that a go.
RE: Latitude by Polaris - PeterB - 07-30-2024
I have a "commercial edition" of the Nautical Almanac published by Paradise Cay Publications. This is the version I usually purchase and it does not contain the "Q " correction tables, nor have I previously used that method. It does have the "a" tables on pages 274 to 276.
I do have a H.O. 249 Vol I which has the "Q" correction tables in the back of that book, but those tables are not included in H.O. 249 Vol II or Vol. III.
Also in the back of H.O. 249 Vol I is a separate set of tables for finding the Greenwich Hour Angle of Aries from which you derive a Local Hour Angle of Aries using an Assumed Position to eliminate any arc-minutes in the computed LHA. The result should be the same LHA that you would achieve by using the more commonly used methods of looking up the GHA of Aries in The Nautical Almanac's daily Pages and using the Increments and Corrections tables.
Here is a link to an article explaining the two methods and referencing the H.O. 249 Vol I tables:
https://oceannavigator.com/two-methods-of-using-polaris-for-finding-latitude/
Their example is for 2008 and my Vol I just happens to include that year so it was easy for me to follow. If you have a newer (or much older) H.O. 249 Vol I your dates may not cover that year -- but it doesn't matter anyway because you can just use The Nautical Almanac to find the GHA for your particular date and skip using the H.O. 249 GHA Aries tables altogether.
Thanks for bringing this to our attention. Always interesting to see/learn something new!
PeterB
Sandy wrote:
"The Mary Blewitt book Celestial Navigation for Yachtsmen gave me nightmares for years and years!"
I have to agree. I struggled with that book also. Years later, after having gained at least a solid understanding of the basics of Cel-Nav, I went back to it to see if it was my impatience or thick headed-ness that was the problem, and instead found the book was (and is) difficult to follow. It is a classic in the field but there are better books out there now. You will do fine with Burch's book. It is a good one.
One book that made things finally "click" for me was "Down To Earth Celestial Navigation" by Russell Sher available as a Kindle e-book from Amazon. The version I got scrambled the tables and work sheets, but the step-by-step descriptions of how to work various sights was easy to follow. I could not recommend it as your ONLY book to study on the subject, but it makes a good companion to some of the other fine works available.
I have no affiliation with Amazon or Russell Sher.
PeterB