[time-nuts] Time-zones and World time..

[Brooke Clarke]

Hi Hal:

A sextant is just an angle measuring instrument so can be used in a number of 
ways.  The classical way is to measure the elevation angle of any heavenly 
that's in your almanac.  Note you can determine your latitude from any of these 
elevation measurements.

The method called "lunar distance" is a more accurate way to get a position fix 
than the classical elevation method.  It requires the sextant be used at odd 
angles relative to the horizon, even horizontal to measure the separation of a 
star and the moon.

Have Fun,

Brooke Clarke
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Hal Murray wrote:
>> One can, of course, observe meridian passage for a variety of stars at
>> night, and from that determine the time (given a calendar and the
>> appropriate almanac data), so you could directly observe midnight. 
> 
> What does "directly observe" mean?
> 
> Stars aren't conveniently located where I want them.  I think I'd have to do 
> something like time when a star that's close to midnight crosses a 
> north-south line in the sky that's above my location.  So in addition to the 
> almanac, I also need a (good?) compass.
> 
> Maybe I don't understand how navigation by sextant works.  They get latitude 
> from the elevation of the sun above the horizon.  Do they also get time 
> (local noon) by noting when the sun is highest?  I think that would be hard 
> to do since you are looking for the peak of a sine curve.  That has a broad 
> flat top.  There isn't any conspicuous peak.  Do the numbers work out?  Can I 
> get the peak close enough to be useful for navigation?
> 
> 
>> Don't forget too, that solar noon varies quite a bit (minutes) from
>> "mean solar time" over the year.  If you're navigating your ship with
>> noon sun sights, this is pretty important. 
> 
> What do I google for if I want that correction?
> 
> There are quite a few time scales.  Which one do navigators use?
> 
> 
>