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From: António Canas (no email)
Date: Sat May 08 2004 - 09:40:06 EDT
In his "Geographae" Ptolomey presents a few longitudes found by himself,
or some other person, using lunar eclipses. And he ask the astronomers to
use every eclipses to find longitudes, so they can use it to make more
acurate maps representing all the world.
Of course, the acuracy of the observation at his time wasn't the same that
we can obtain today. But the other way that they have to obtain the
coordinates of a place, by "dead reckonig" was less acurate than the
eclipses.
I think the Chinese have done this, in the 15th century, in a way similar
to those proposed by Ptolomey, and obtain the same acuracy. .
Antonio Canas
----- Original Message -----
From: "Philip Bailey" <>
To: <>
Sent: Saturday, May 08, 2004 2:02 PM
Subject: Re: 1491 The year China discovered longitude
> On Saturday 08 May 2004 11:07 am, Antonio Canas wrote:
> > Just try to read something from Claudius Ptolemy who lived from 85 to
165 a
> > few centuries before "The year China discovered longitude"
> >
> > You can find that he explains how to use eclipses to find the
longitude of
> > places
>
> I suspect Kieran Kelly's question is about the practicalities of
actually
> finding your longitude by lunar eclipses, rather than coming up with the
> concept of doing it. Did Ptolemy find his longitude by this method? I
don't
> know; but it would seem surprising if he had.
>
> Kieran Kelly asks whether the list can think of a way the Chinese could
have
> done this in the 15th century.
>
> Philip Bailey
> 50:49N 0:6W
>
>
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