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Hi Lucio,
Thanks for your note but I don't agree with your
argument.
In all books about gnomonics, old and new, temporal
hours, Italian hours, Babylonian hours and so on are based on the formula
for half the daylength T :
cos T = - tan phi tan decl.
This means that all calculations and constructions
are based on the center of the sun.
Of course it is easy to calculate with respect to
the limb of the sun now we have computers to help us but to my opinion this
isn't usualy done in gnomonics.
In our daily life indeed the sunrise
and sunset is calculated with respect to the limb of the sun. But gnomonics
isn't used in our daily live and I prefer to act in
the historical way.
Best wishes, Fer.
Fer J. de Vries
----- Original Message -----
Sent: Sunday, September 26, 2004 6:15
PM
Subject: R:
I am worthwhile with how much you write, to exception of the following affirmation:
"Temporal hours are calculated in respect to the center of the sun as we do
for other time systems".
The hours temporarie, italic and babiloniches are reported to the sunset or
to the sunrise; the sunset and rising are, for definition, reported to the
superior limb of the Sun; therefore it is inaccurate to refer to the center of
the Sun and this yeld to an error of about 4 minutes.
Being complicated to establish the transit of the center of the Sun on the
line of the horizon is unlikely, neither it results me, that followed this
method in the antiquity when instead it is simple to refer to the superior
edge.
Best wishes, Lucio
-----Messaggio
originale-----
Da: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]Per conto di Fer J. de
Vries
Inviato: venerdì 24 settembre 2004 12.22
A: Noam
Kaplan; sundial
Oggetto: Re:
Hi Noam,
Of course the refraction effects the hourangle
of all the time systems we use in dialling.
But also keep in mind the historical meanings
of used systems as the temporal hours.
Temporal hours are calculated in respect to the
center of the sun as we do for other time systems.
The times of sunrise and sunset however are
calculated for the limb of the sun.
Should we care about that either?
We want to have time in seconds and even in
smaller parts.
But in older days the feelings about time was
much different.
Temporal hours were used as a period of time
peolple was in, not an exact moment of time as we often use.
Calculating the temporal hour lines shows that
the lines aren't straight but sligthly S-shaped which is best visible with
increasing latitude but in older dials
the lines are drawn as straight lines.
It's good to think about the effect of
refraction but in general I should say, forget the refraction in
dialling.
Best wishes, Fer.
Fer J. de Vries
----- Original Message -----
Sent: Friday, September 24, 2004
12:30 AM
Can anyone answer this?
If this is the wrong forum, I
apologize.
I have a calculation to figure out the
atmospheric refraction from Fred Sawyer's article in the NASS Compendium.
It is based on calculations that Meeus brings in his book. Refraction
changes the apparent altitude of the sun, thereby changing both the
apparent declination and apparent hour angle of the sun.
Am I making a mistake when I use the apparent
declination and apparent hour angle for the temporal hour
calculation?
The effect of a few seconds difference
for atmospheric refraction on the hour angle seems to have a much
bigger effect on the temporal hours.
Thanks for any help you can
offer,
Noam
My calculations can be seen on the web at
in the function
temporal(localTime)
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