Hi Jack,
In addition to the responses you get, the etymology of the Greek word
'analemma' is interesting.
In early Greek language 'ana' may imply some motion or at least
extension and means up along, up through.
'lemma' derives from 'lambano' = receive
'analemma' is what you receive or see from above, a top view
Therefore the word is used by the Roman engineer architect Vitruvius
to refer to a graphical construction, equivalent to today's
orthographic projection.
This ethymology explains the use of 'analemma' in 'analemmatic
sundial". An analemmatic sundial is an orthographic projection of an
equatorial sundial.
See http://www.fransmaes.nl/zonnewijzers/welcome-e.htm go to
Analemmatic - extra info
Willy LEENDERS
Hasselt in Flanders (Belgium)
Visit my website on the sundials in the province of Limburg in
Flanders (Belgium) and on worthwhile facts about sundials
www.wijzerweb.be
Op 15-nov-2009, om 0:18 heeft Jack Aubert het volgende geschreven:
I recently revised my notes for a sundial talk I was giving which
included a section on the EOT, and its connection with the
traditional figure 8 analemma. I wanted to explain its origin, or
at least be able to answer the question if asked, but have not been
able to find any believable references on how it emerged. I
assume that the source of the figure is simply a “connect the dots”
picture of what the sun, or a gnomon pointer will trace it out over
the course of the year projected onto a surface. But I do not see
how the dots can be generated without using an external non-solar
source of time.
The Wikipedia article on the EOT has a confusing statement to the
effect that Ptolomey was aware of the variation in the sun’s
movement and even devoted a chapter to the subject, but then says
that he did not correctly account for the two sources of
variation. Is there any evidence that the Greeks or Romans ware
aware of, and used, the analemma representation, perhaps generated
by reference to a clepsydra, or did it first appear when mechanical
clocks became prevalent?
Jack
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