[aprssig] Re: [[furlongs per fortnight]]

[Mark Fellhauer]

At 11:57 AM 9/7/2007, Steve Dimse wrote:

>On Sep 7, 2007, at 1:05 PM, Mark Fellhauer wrote:
>
>>You follow a celestial reference point.   Um, that would be a star.
>
>In an imprecise sense you are right, in that the sun is a star. The
>first known measurement of the earth's diameter was calculated using
>the angle of the sun during the summer solstice.


The first modern sextants recorded in history can be dated back to 900 AD 
in Iran.  But various astrolabes were in existence much earlier than 
that.  And Stars other than the sun were often used for 
reference.    People do navigate at night.

While some Romans had mis-calculated the earth's diameter, there were 
certainly people with more accurate measurements.   Columbus used "facts" 
under-reporting the earth's diameter probably on purpose to mollify crew 
members and his financiers.

By 1612 longitude could be determined by time tables derived from the orbit 
patterns of Jupiter's moons.


Mark
KC7BXS