Re: VMs: How did Ptolemy know about time zones

[Pamela Richards <spirlhelix@xxxxxxxxx>]

Hi, Dan!

Thank you for the useful information about early uses
of the gnomon!  Yes, the altitude of stars and planets
tells us something about what we now call latitude. 
That's what I was attempting to say about the eclipse
seeming to take place higher in the sky for the person
in the West, although you have provided lots of good
examples of the principle.

Boy, those Nabateans must have gotten around!  I was
wondering also, before you sent your post, how much
knowledge about time, travel, and the position of the
Sun or stars might have been gathered by sailors. 
You've answered the question I did not ask!

Yes, Ptolemy used latitude and longitude both in his
books on geography; he also had a system of
representing the sphere of the earth on a flat page.
Unfortunately for Columbus, although Ptolemy's maps
inspired him to attempt China by the "back door",
Ptolemy's knowledge of New World geography was lacking
and he showed China much closer to Europe than it
actually was.


Warmly,

Pam


 As a geographer, 
> Ptolemy's reputation rests mainly on his Geographike
> hyphegesis (Guide to 
> Geography), which was divided into eight books; it
> included information on 
> how to construct maps and lists of places in Europe,
> Africa, and Asia 
> tabulated according to latitude (and longitude I
> believe, although I do not 
> know how he would have calculated these. Pamela, do
> you know if he 
> calculated longatude?
> 
> There are, I understand, many errors in the Guide.
> For example, the Equator 
> was placed too far north, and the value used for the
> circumference of the 
> Earth was nearly 30 percent less than a more
> accurate value that had already 
> been determined before, as well as some
> contradictions between the text and 
> maps. The Guide is an important work from a
> historical point of view 
> because, like the Almagest, it exerted a great
> influence on later 
> generations. Christopher Columbus, for example, used
> it to strengthen his 
> belief that Asia could be reached by traveling
> westward because Ptolemy had 
> indicated that Asia extended much farther east than
> it actually does. 
> Ptolomey suggested that the Indian Ocean was bounded
> by a southern 
> continent. (Perhaps reports from Arab merchants of
> Australia, Antarctica and 
> South America caused him to think this. There are a
> number of research 
> projects currently going on to find and record all
> of the old Arabic 
> inscriptions in South, Central and North America.)
> It wasn't until the 
> return voyage from the Southern Hemisphere by Capt.
> James Cook that the 
> belief in a southern continent was disproved.
> 
> I have looked at the star charts in the VMS, but
> since so much was known by 
> 100 BC it is very hard to date the VMS by what is
> shown. If only we could 
> read the labels under the charts! 
> 
> 
>
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=====
"I'd rather learn from one bird how to sing, than to teach ten thousand stars how not to dance."


		
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