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. |
|
|
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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
|
©
2009 J. Giesen
