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Completely unrelated, but stemming from the same article.

The author states that height can only be known to some few cm or
whatever because of variations in gravity, if I remember correctly.
It would seem that this is due to our tradition of assuming we are on
the surface of a spheroid or ellipsoid when doing navigation.
Confining ourselves to a surface makes the trig easier, but couldn't
one position oneself with greater accuracy (with feet firmly planted
on earth, not on a boat) using only stars or stars plus the sun,
ignoring the earth's horizon, by measuring star-star distances?  Make
it a true 3-D problem.  Or would uncertainties in the positions of
stars still hamper ones efforts, especially uncertainty in their
distance from us?

Fred Hebard

On Apr 14, 2008, at 9:50 PM, frankreed@HistoricalAtlas.net wrote:
>
> The fascinating article which Fred Hebard linked:
>  http://www.physicstoday.org/vol-59/iss-3/p10.html
> includes a detailed discussion about the problems of gravitational
> time
> dilation and extremely accurate clocks. That's the main topic, and
> it's
> great stuff.
>
> The article also mentions leap seconds and navigation:
> "Celestial navigators --that vanishing breed-- also like leap
> seconds. The
> Global Positioning System, however, cannot tolerate time jumps and
> employs a
> time scale that avoids leap seconds."
>
> So here's my question: what's the best way of doing celestial
> navigation if
> leap seconds are dropped from official time-keeping? I don't think
> it should
> be all that difficult to work around, but I'm not sure what the best
> approach would be. Assume we get to a point where the cumulative time
> difference is, let's say, 60 seconds (that shouldn't happen for
> decades, so
> this is just for the sake of argument). Should we treat the
> difference as a
> 60 second clock correction before working the sights? Or should it
> be a 15
> minute of arc longitude correction after working the sights? Or
> something
> else entirely??
>
>  -FER
> Celestial Navigation Weekend, June 6-8, 2008 at Mystic Seaport Museum:
> www.fer3.com/Mystic2008
>
>
>
> >



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