NavList:

   

Reply

At 22:45 01/08/2008, you wrote:
>
>
>As I recall they're Natural Logs.  HewS
>
>On 8/1/08, mike boersma  wrote:
> >
> >  Does anyone know the derivation of the numbers in the N(x) table on
> >  the Emergency Navigation card from Starpath.
> >---~------~--~---

To be more specific, N(x) is the natural logs of sines, signs changed and
decimal point moved appropriately.

One little wrinkle in the sight reduction method as laid out on that
Emergency Navigation Card that you may want to watch out for.

Where Dec and Lat have the same name and the meridian angle t is < 90, then
u = Lat + (90 - w), which is as written on the card.

But where Dec and Lat have the same name and the meridian angle t is > 90,
then u = Lat - (90 - w). This rule is not on the card.

The meridian angle cannot be greater than 90 for contrary names, so no
change to that rule.

It may argued that the Emergency Almanac is "for the Sun" and so it is
unlikely that the meridian angle is going to be greater than 90 degrees.
True for lower latitudes, but in mid summer in high latitudes, the meridian
angle of the sun will be easily > 90 in the early morning or late evening.

I have a few other little quibbles with the card, which David Burch knows
all about. But that does not detract from the fact that getting all that
navigation information on one piece of card is a great achievement by
David.  It is a good lesson in just what is actually important in celestial
navigation, and what is mere detail.

When I was visiting David in his Starpath HQ in Seattle last September, we
went outside with a simple astrolabe David had made with a protractor, some
cardboard and a piece of string. We took a careful altitude of the sun and
got an LOP about 8 nm of where it was supposed to be. A good lesson that
very simple instruments costing a few dollars to make, will give quite
acceptable results - and are great fun to use!

Geoffrey Kolbe


--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply