Quadrans Vetus
| This quadrant is
a portable altitude sundial for a single latitude
indicating the unequal hours (planetary hours),
dividing the time intervall from sunrise to sunset
into 12 hours. The instrument is equipped with a simple Sun sight on one edge. A weighted thread with a sliding bead is hanging from the apex. |
See
instructions for interactive use below
   |
Enter
the latitude
(decimal degrees) into the text field and hit Return key. The latitude is indicated in the lower left. |
 |
The
interactive regions (light gray scales) are changing
the cursor to cross hair. |
 |
Click into the light gray date scale to set
the bead. Inner scale: Jan - Jun, or outer: Jul - Dec. |
 |
Using the declination scale will return two dates. Choose one of them by clicking the inner or outer date scale. |
 |
Click into the light
gray altitude degree scale on the
limb to direct the sight to the Sun. |
 |
The scale of the
unequal (planetary) hours: 0 = sunrise, 6 = noon, 12 = sunset. |
 |
Read the unequal
hour (e.g. between 4 and 5: 4.5 or 10.5). |
 |
Using the "Today"
button the bead is set to the 6th hour (noon) of the
current date. |
|
Accuracy of the
Quadrans Vetus
Comparing the
quadrant with modern astronomical calculations (my Planet
Clock applet) it can be stated that the
results of the quadrant become more inaccurate for
higher latitudes and higher declination. The error
is 0 at rise (unequal hour 0), noon (unequak hour
6), and set (unequal hour 12), and has a maximum in
between. |
| Declination | 30° N |
55° N |
| 0° | 0.05 hours |
0.1-0.3 hours |
| +11.7° | 0.08 hours | 0.15 hours |
| +23.4° | 0.13 hours | 0.35 hours |
| Books |
| Morrison,
James E.: The Astrolabe, Janus. Softcover edition,
2007, Rehobot Beach, DE USA, ISBN-10: 0939320304, ISBN-13: 978-0939320301. Details... Hügin, Johannes: Das Astrolabium und die Uhr, Ulm, 1978, ISBN 3-921348-23-4. Rohr, René R. J.: Die Sonnenuhr. Geschichte, Theorie, Funktion. Callwey, München 1982. Meyer, Jörg: Die Sonnenuhr und ihre Theorie. Harry Deutsch, Frankfurt 2008. Zenkert, Arnold: Faszination Sonnenuhe (mit CD-ROM), Harry Deutsch, Frankfurt 2000. |
|
|
|
Quadrant Sundial Gunter's
Quadrant
(J. E. Morrison, PDF) Edmund Gunter biography (MacTutor History of Mathematics archive) Gunter's quadrant (Navigation Museum) Gunter quadrant (The Whipple Museum) A Gunter quadrant and practical
knowledge (The Whipple Museum) Gunter quadrant (National Maritime Museum) The
Electric Astrolabe (J. E. Morrison) Astrolabium
(Deutsches Museum) Der
Gunter-Quadrant (Gunter W.) Das
Astrolab (Informatik Uni Erlangen) Keith's Asterolabe (Java applet) Literature on astrolabes (M. Brunold) The Uses of History in Science Education
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©
2009-2023 J. Giesen
