Virtual Sundial Virtual SundialClick here to see the Virtual Sundial or read on for information.
This page links to a Java applet showing a real-time simulation of a sundial. The initial dial geometry is that of the sundial at Queens' College Cambridge, but you can change the settings to any plane geometry at any location in the world. For hints on reading the Queens' sundial, click here.
This is a proof of concept. There is only a rudimentary user-interface. Only the mean sun is displayed. There are no decorations or annotations.
Java v1.1 applet support is required in the browser. This rules out v3.x browsers. JavaScript LiveConnect support is required if you wish to change the dial settings: this works in Netscape, and in MSIE for Windows v5 or higher; it does not work in MSIE for Mac.
An alternative version for browsers that support Java applets via plug-ins using the EMBED tag is here.
This program simulates sundials with a flat plate. The flat plate of a sundial is an example of what is known mathematically as a plane. The orientation of a plane in space is specified completely by the direction of its normal, a line perpendicular to the plane. Two parameters are sufficient to uniquely specify the direction of a line in space, and hence the orientation of a plane. This program requires a specification of sundial plate orientation which is equally valid in the northern or southern hemispheres. The chosen method is to specify the direction of the normal in the local horizon coordinate system used by astronomers. The local horizon coordinate system is a type of spherical coordinate system in which a direction is specified by two parameters: the Azimuth (measured in degrees along the horizon from North), and Altitude (measured in degrees up at right-angles from the horizon). These terms are not normally used by diallists. The correspondence to diallists' terminology is as follows.
Azimuth: In the northern hemisphere, a dial described as South declining 15 degrees West has a normal with Azimuth of 180+15 = 195 degrees. A dial described as South declining 9 degrees East has a normal with Azimuth of 180-9 = 171 degrees.
The Altitude of the normal corresponds directly to what diallists know as Reclination.
2002 Apr 3: corrected bug causing sun's shadow to be misplaced if a nodus shift was in effect.
2000 Apr 30: Clipping of altitude lines implemented more properly.
2000 Apr 17: Changed temporal hour line colour from magenta to cyan to reduce confusion with altitude lines. Bug fixes for clipping of azimuth lines. Another Java-AWT drawing problem worked around.
2000 Apr 12: Added the ability to display British Summer Time in the local time (this daylight saving zone is not normally available in Java 1.1.x). Most USA daylight savings zones should already work. If the browser supports Java 1.1.6 or higher, then various other regional daylight savings schemes should also display correctly. Otherwise, the local time zone will be displayed as an offset from GMT.
2000 Apr 3: Added ability to shift nodus horizontally and vertically.
2000 Mar 30: Temporal hour lines added, coloured magenta. A temporal hour is a type of unequal hour in which the period between sunrise and sunset is divided into 12 equal parts, which vary in length according to the season of the year, equalling mean hours only at the equinoxes.
2000 Mar 28: Internal clipping implemented to work around AWT masking all integer coordinates to 16 bits before using them.
2000 Mar 27: Minor drawing bug fixes.
2000 Mar 26: A start has been made on clipping the colouring of the constant-azimuth lines to the area contained within the solstice lines, leaving a faint line outside in circumstances deemed interesting. Some terminology revised.
2000 Mar 20: The Vernal Equinox: first trial public release.
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