analemma and equation of time: when first understood

From: mack (jmack_at_wm7d.net)
Date: 08/29/04 

Date: Sun, 29 Aug 2004 13:10:50 +0000

The analemma, photographed by Dennis DeCicco and now appearing in
schoolyards and driveways all over the world, and whose image on globes
of the earth mystified generations of school teachers, and the equation
of time that says that the sun can be ahead or behind the mean sun by upto
15mins, depend on the orientation of the earth's axis with respect to the
plane of the ecliptic and on the ellipticity of the earth's orbit.

I haven't been able to find any historical information as to when people
first knew about this. Presumably once Kepler understood that the planets
moved in ellipses (1609), it was possible to realise that the sun would
be slow or fast at different times of the year. Once clocks could measure
time to within 15mins over a period of a year (late 1700s with Harrison's
chronometers), then you could observe that the sun was fast or slow.

Possible starting points might be:

When did corrections for the equation of time first appear on sundials?

When did the analemma first appear on globes of the earth?

I remember many years ago, seeing an article in S&T about the
shape of analemmas on other planets, but this was before I subscribed
to S&T. The S&T on-line index only goes back to 1996 and doesn't show this
article. Does anyone know when it was published?

Thanks Joe 

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!

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