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

[Hal Murray]

> 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?



-- 
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