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View Full Version : Astro Navigation By Tim Bartlett - Possible Error

Talulah
18-09-09, 20:49
Question for anyone who has this book:
On page 37 the author looks up the entries correctly for N23 rather than N23 degrees 26.3 minutes.
However, over the page he then looks up the correction for minutes of declination and uses the row for 23 and not the row for 26 minutes. Am I missing something or is this an error?
Thanks.

(Just found the authors web site so have sent him a message.)
VO5
19-09-09, 14:03
Interesting.....

I have not seen the book.

The classical method of dealing with minutes of arc in Lat or Long is to interpolate.

I will explain:-

Conventionally 6' of arc = 1/10 of one degree.

Then between one level of latitude and another in whole numbers thre is a correction applicable to each.

Then in this case one correction is subtracted from the other and then the fraction in difference is applied to give an accurate value, which is called an "argument"", with which to be able to carry on the calculation accurately.

The same applies for Longitude.

I hope this helps.
Talulah
21-09-09, 20:28
The book has only just been released by the RYA.
The Author has come back regarding my query and confirmed it is an error.
The book itself is well laid out, plenty of pictures, easy to follow etc.
I have been debating on which book to use as a coursework book when teaching the Ocean Theory course hence my interest in it.
smartcom
23-09-09, 09:30
Why not have a look at WinAstro (www.winastro.co.uk) for checking those sight reduction calculations?
Talulah
23-09-09, 18:32
Why not have a look at WinAstro (www.winastro.co.uk) for checking those sight reduction calculations?

Downloaded the app. Whilst it looks dated the functionality looks pretty good. I shall spend some time having a play around. The next Ocean Theory course I am teaching is at the start of November so I shall master it and then demonstrate it to the students.
chart5011
25-09-09, 10:34
A brilliant book on this subject, sadly out of print, is 'Navigation for Offshore & Ocean Sailors' by David Derrick. You may be able to pick up a secondhand copy. Very clear with exercises after each chapter.
duncanmack
25-10-09, 18:30
A brilliant book on this subject, sadly out of print, is 'Navigation for Offshore & Ocean Sailors' by David Derrick. You may be able to pick up a secondhand copy. Very clear with exercises after each chapter.

Navigation for Offshore and Ocean Sailors is available from Amazon. :)