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Date: Sun, 29 Jun 1997 08:59:19 -0700
From: Luke Coletti <[EMAIL PROTECTED]>
Organization: GrokSundials http://www.groknet.com
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To: "fer j. de vries" <[EMAIL PROTECTED]>
Subject: Re: analemma
References: <[EMAIL PROTECTED]> <[EMAIL PROTECTED]> <[EMAIL PROTECTED]>
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fer j. de vries wrote:
>
> What do you mean with analemma in your question?
>
> As Vituvius describes in his book De Architectura it is a construction
> by which it is possible to find the suns height and azimuth and by which
> you can lay out sundials.
> But for that no regular timepiece it needed as you write.
>
> In English nowadyas analemma is used for the equation of time curve but
> that has nothing to do with the analemma of Vitruvius.
I wasn't aware of an additional meaning so I am inquiring about the
analemma that we know today by (eot vs dec). The mention of water clocks
being used to calibrate sundials once again sparked my interest in
knowing more about the history of the analemma. My interest is in
knowing who when and by what means the (eot vs dec) analemma was
'discovered'. Was a regular timepiece employed? If so, which kind?
I did recieve a forwarded reply (see below) via the History of
Astronomy list that makes me even more interested in Ptolemy's On the
Analemma, which appeared as a thread here on the list and which I'm
assuming is the source for some of the text below.
>
> The analemma is of course equivalent to knowing the equation of time, and
> it follows, for example, from Ptolemy's analysis of the difference
> between mean and true motions of the sun. This requires (in his case)
> determining the eccentricity of the sun's orbit. This Ptolemy proposes
> to show by times of solstices and equinoxes, which he takes essentially
> from Hipparchus. However, it is quite difficult to determine a solstice
> exactly, and it is interesting to see that Hipparchus' solstice value
> conforms to the Babylonian tables. How did the Babylonians do it? One
> of the most intriguing suggestions, by K.P. Moesgaard, is that they
> deduced it from the uneven spacing of lunar eclipse positions in the
> sky. The reason I give all this detail is to indicate that it was not
> necessary to have a mean time clock such as a water clock to get this
> information. It seems highly likely that the equation of time was
> determined in some other, round-about but highly ingenious way, such as
> the one I have mentioned.
> OWEN GINGERICH
Also, since this brings up Ptolemy again, Mike Mickelson provided me
with a resource (see below) for obtaining an annotated copy of Ptolemy's
On the Analemma.
> Title of dissertation: Ptolemy's "Peri Analemmatos" an Annotated
> Trascription of Moerbeke's Latin translation and of the Surviving Greek
> Fragments with an English Version and Commentary.
>
> By: Don Raymond Edwards
> Dissertation, Brown University 1984.
Regards,
Luke
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