Dear Fabio,
Many thanks for your photograph and
explanation. This is just what I
needed. I see that the heliodrome is
'the region of the celestial sphere
bounded by the two tropics and the
local horizon'.
I now appreciate that I have been
designing heliodromes for 40 years
without knowing it!
When I first read your message I
had two thoughts:
1. For a sundial to show a
heliodrome it must have
a nodus.
2. A sundial can never show
the whole heliodrome because
any real sundial has edges.
Both thoughts are WRONG.
I attach an image of a paper sundial
that I designed last year and you
can see:
1. There is no nodus.
2. The surrounding circle is the
projection of the horizon so
you can see the WHOLE heliodrome.
I think I shall use this word more
frequently!
Frank
Frank King
Cambridge, U.K.
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