NavList:

Gary adds:

Some more useful information:

An easy way to practice with a sextant and to take a number of
observations to allow you to determine its accuracy is to use the
meridian transit of Polaris. When Polaris is crossing the meridian it
is moving horizontally and its altitude doesn't change. For the period
of more than 15 minutes both before and after meridian passage the
altitude of Polaris changes less than one - tenth of a minute (0.1').
For a period of 34 minutes before and after passage the altitude of
Polaris changes less than one half minute (0.5'.) For 48 minutes
before and after its altitude changes less than 1 minute.

Calculate the time that Polaris is crossing your meridian and get out
early and start shooting. It is about 10:46  pm local time now (Nov. 21, 2007) depending on your exact longitude..
 Calculate the altitude by adding your latitude to the polar distance of Polaris,
now 41.9 minutes, and then ADD the refraction correction (yes ADD) which
will then give Hp (precomputed altitude, this is how it is done by
flight navigators) because this porceedure allows you to compare your
Hs directly with Hp to determine the intercept immediately, or the
error in the observation if taken from a known point. If shooting a
lower transit subtract the polar distance from your latitude. You only
have to update this Hp from time as the declination of Polaris changes
slowly.


Here is a link to a site that will give you celestial almanac data and compute Hc for you.

http://aa.usno.navy.mil/data/docs/celnavtable.php

Here is a link to a site where you can download for free the current
copy of Bowditch as well as H.O 229, H.O 249 etc:

http://www.nga.mil/portal/site/maritime/?epi_menuItemID=c56aa099e2bff...

Here is a link to an online version of Bowditch:

http://www.i-DEADLINK-com/bowditch/

Here is a link to an online Nautical Almanac:

http://www.tecepe.com.br/scripts/AlmanacPagesISAPI.isa

Her is a link where you can download a celestial navigation program:

http://www.tecepe.com.br/nav/

Enjoy.



Isonomia wrote:

Gary,

thanks a million for the link to the book with navigational astronomy
calculations etc. although it's a lot to go through, it was exactly
what I needed.

Mike

On Nov 20, 7:31 pm, glap...@pacbell.net wrote:
  

Gary LaPook writes:

Also attached is a link to an online version of The American Practical
Navigator refrence work, go to chapter 19.

http://www.tecepe.com.br/scripts/AlmanacPagesISAPI.isa

http://www.i-DEADLINK-com/bowditch/

    

learnt spherical geometry at University, I'm a little  rusty)
      

--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---