Apian Card Dial
Uhrentäfelchen
| This instrument
is a portable sundial for a single latitude, developed
by Peter Apian (Petrus Apianus, 1495-1552). It also
indicates the time of sunrise and sunset. It is equipped with a simple Sun sight on the upper edge. A thread with a sliding bead is hanging from the point of suspension (at the end of a brachiolus) which is adjustable in two dimensions (declination, latitude). |
See
instructions for interactive use below
Quadratum Horarium Generale (Regiomontan Dial)
Capuchin Dial (single latitude)
 |
Enter
the year
into text field and hit "Apply input". (Gregorian Calendar only, later than 1582) |
  |
Enter
the latitude
(decimal degrees) into the text field and hit "Apply
input". The latitude is indicated in the text field. |
 |
The
interactive regions (light gray scales) are changing
the cursor to cross hair. |
 |
Click into the
degree scale (light gray) on the lower and left limb to
direct the quadrant to the Sun. The thread will follow
the elevation angle. |
 |
Use the "Today"
button to set the thread to the current date. The bead
is set to the current Sun's declination. |
 |
-
Click into the light
gray date scale
to set the thread. |
 |
The checkbox
"Fix Lat." is an option to keep the latitude when
clicking into the date/latitude scale. |
 |
Read
the date, the declination, and the time of sunrise and
sunset (neglecting refraction on the horizon), the
equation of time, the current time, and elevation as
computed by astronomical algorithms. |
| Select
from the "Display Options" menu. |
|
| The
red frame of the applet area is a square (753 x 753
pix, same size as for Gunter's quadrant). |
|
| The dial is
obeying the equation of the nautic spherical triangle
(h = elevation angle,
φ = latitude, AH =
hour angle):
sin h = sin φ sin δ + cos φ cos δ cos AH
A very short proof can be found in the book
of Rohr.The formula is symmetric with respect to φ and δ, thus the dials of Regiomontanus and Apian are equivalent. |
Under construction!
| Books |
| Rohr,
René R. J.: Die
Sonnenuhr. Geschichte, Theorie, Funktion. Callwey, München 1982. Meyer, Jörg: Die Sonnenuhr und ihre Theorie. Harry Deutsch, Frankfurt 2008. |
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Regiomontanus, Apian and Capuchin
Sundials
Das
Allgemeine Uhrentäfelchen von Regiomontan Tragbare Sonnenuhren in Europa ab 1400 Uhrentäfelchen von P. Aegid Everard Pourquoi le cadran de Regiompntanus fonctionne-t-il ? Horoscopion Apiani Generale Dignoscendis
Horis cuiuscumque generis aptissimum |
©
2009-2023 J. Giesen
