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As Fer has correctly
pointed out, the sign of the angle Mu (inclination of the equinoctial line on
the horizontal) in my formulas must
be taken with the minus sign if the plane is turned toward southeast: I
apologize for not having specified in my preceding message.
I use
the following convention:
if,
looking at the plane, the equinoctial line climbs going toward right, and
therefore the plane is turned toward West, the angle Mu must be taken as
positive.
If,
otherwise, the line climbs going toward left (plane turned Eastward) the angle Mu must
be taken as negative.
Obviously for the stained glass sundials it is
necessary to not look at the dial from the inside but from the outside, with
our shoulders turned toward the Sun. In
the 1529 sundial (when we look it from the inside) the equinoctial line
climbs going toward right and therefore climbs going toward left if we look at
the dial from the outside . Note
In my
precedent message I have said that the method can also be used for sundials with
Italic hours (frequent in It is
necessary to follow these simple substitutions: Hour
angle = N*15 deg with
N =
modern hour (apparent local time) - 12
N = Italic hour - 18 N = Babylonian hour - 6 N =
temporary hour - 6
For
example for the Italic hours 15 and 20 we have the values N1=-3 and N2=+2 This
because on the equinoxes, the
followings relationships are valid:
Hit = 6+Happ_time; Hbab = Hit - 12; etc.
Best Gianni Ferrari |
