Gunter's Quadrant Applet
| Edmund Gunter
(1581-1626), a mathematician and astronomer, first described his
quadrant, a simplified version of the
Arabic astrolabe, in the 1623
publication "De Sectore et Radio". The quadrant presented here
was produced by the eminent instrument maker Henry Sutton in 1657. It
was used to tell the time
of day and to simplify
astronomical calculations for the Sun (altitude, azimuth, declination,
right
ascension, position of the Sun in the zodiac). 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
Quadratum Horarium
Generale (Regiomontanus Dial)
 |
Enter the year into text field and hit Return key. (Gregorian Calendar only, later than 1582) |
  |
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 part of the declination
scale to set the bead (set the date first). |
 |
Click into the
degree scale (light gray) on the limb to rotate the thread. |
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Use the
"Today"
button to set the thread to the current date. The bead is set to the
current Sun's declination. |
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- Click into
the light gray
calendar (date scale, inner part for
winter and spring, or outer
part for summer and autumn) to set the thread to the date. - To set the bead to the declination then click within the region of the hour curves on the point where the thread crosses the 12 hours curve. - Then click into the degree scale (light gray) to rotate the thread and the bead. |
 |
Read the angle,
and the date within the
shadow
square. The values
(for 0 UT) of the declination,
the ecliptic longitude
(and position in the zodiac),
the right
ascension, and the times of rise
and set (local apparent time)
are computed and
shown within the shadow
square. |
 |
Select from the
"Display Options" menu. |
  |
Setting a
date will enable the button "Table", which opens a list of the Local
Apparent Time, the Standard Time, the altitude of the Sun, and the
azimuth angle (East of North, and West of South). |
Thanks
to
James
E.
Morrison
(Janus) for the instructions making the Quadrant.
The
zodiac
and
the
ecliptic
longitude:
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 |
 |
 |
 |
 |
 |
 |
 |
 |
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| Aries | Taurus | Gemini | Cancer | Leo | Virgo | Libra | Scorpio | Sagittarius | Capricornus | Aquarius | Pisces |
| 0° - 30° |
30° - 60° | 60° - 90° | 90° - 120° | 120° - 150° | 150° - 180° | 180° - 210° | 210° - 240° | 240° - 270° | 270° - 300° |
300° - 330° | 330° - 360° |
The
zodiac
symbols
are
from
the MarVoSym font, used by the applet.
| J2000 | RA | Declin. | mag | |
| Arcturus |  |
213.92° | 19.18° | -0.05 |
| Aldebaran |  |
69.98° | 16.56° | +0.853 |
| Examples for
use of the digital Gunter Quadrant on 2009, Aug. 10 More Sample Problems in the PDF of James E. Morrison |
|
|
1. Find the
declination of the Sun:
Set the date
and the thread by clicking into the outer date scale.
Click on the intersection point of the 12 Hours line and the thread to set the bead. Turn the thread to the declination scale by clicking at lower left end of degree scale, and read the declination at the bead: 15.7° (computed: 10.58°) |
  |
| 2. Find the altitude of the Sun at local
noon: Set the date
by clicking into the outer date scale.
Read the altitude on the degree scale (limb): 54.0° (computed: 53.9°) |
 |
| 3. Find the ecliptic longitude (position in
the zodiac) of the Sun: Set the date
and the thread by clicking into the outer date scale.
Click on the intersection point of the 12 Hours line and the thread, setting the bead. Turn the bead to the Ecliptic scale by clicking into the degree scale, and read the longitude angle: 137.0°, Leo 17° (computed: 137.5°, Leo 17.5°) |
 |
| 4. Find the Right Ascension of the Sun: Set the
thread to the longitude of the sun on the ecliptic (see ex. 3,
137°).
Read the angle on the degree scale (limb): 40.5° The Right Ascension is 180°-40.5°= 139.5° (computed: 140.0°) |
|
| 5. Find the time of sunrise: Set the
thread to the date. Click on the
intersection point of the 12 Hours line and the
thread to set the bead. Rotate the
bead to the horizon line, and read the angle on the degee scale (limb):
20.6°
This angle corresponds to 4*20.6 min = 82.4 min. Subtract (as the date is in summer) this time from 6:00 hours to get 4:38 (computed: 4:32) |
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| 6.1 Find the altitude at 3 PM: Set the
thread to the date. Click on the
intersection point of the 12 Hours line and the
thread to set the bead. Rotate the
bead to 3 Hours line, and read the altitude angle on the degee scale
(limb): 39.4°
(computed: 39.2°) |
 |
| 6.2 Find the azimuth at 3 PM: Now turn the thread to the co-altitude 90°-39.4°=50.6°, and read the azimuth angle from the azimuth curves using the bead between the 60° and 70° curve: 62° (North of South). (computed: 61.6°) |
 |
My
prototype
of
Gunter's
quadrant,
set to Aug.10:
Under
construction!
| Books |
| Morrison, James
E.: The Astrolabe, Janus. Softcover edition, 2007, Rehobot Beach, DE USA, ISBN-10: 0939320304, ISBN-13: 978-0939320301. Details... D'Hollander, Raymond: L'Astrolabe. Histoire, theorie et pratique. Institut océanographique, Paris, 1999. ISBN 2-903581-19-3. Hügin, Johannes: Das Astrolabium und die Uhr, Ulm, 1978, ISBN 3-921348-23-4. Stautz, Burkhard: Die Astrolabiensammlung des Deutschen Museums und des Bayerischen Nationalmuseums, Oldenbourg, München 1999. 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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|
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The
Astrolabe (James E. Morrison) 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) R.
Doerfler:
The
Analemmas
of Vitruvius and Ptolemy (PDF) J. G.
Freeman: A Latitude-Independent Sundial (PDF) F. A.
Stebbins: A Mediaeval Portable Sundial (PDF)
|
©
2009 J. Giesen
