Home Search GeoAstro Applets Astronomy Chaos Game Java Physics Quiz

Analemma Sundial Applet

Click into the grid plane to change the gnomon position

 Check your time zone offset and the local time. Select the view details from the "Analemma..." menu. Select latitude (northern positive, southern negative), and longitude (eastern positive, western negative) from the menus. You may use the keys "m", "d", "h", "n" to increase the month, date, hour, minute, or Shift key and "m", "d", "h", "n" to decrease month, date, hour, minute ! Analemma: 1 = Dec 21 - Jun 21 (blue) 2 = Jun 21 - Dec 21 (red)

More of my sundials:

This type of sundial has a vertical rod (gnomon, height H) casting the shadow on a horizontal plane. The shadow of the gnomon's top (point P) is used to read the time (and the date).

Example: Berlin 52.51 N, 13.41 E

October 20 at 15:15, or
Feb 21 at 15:45

 An analemma is the figure-of-eight shape that results if the Sun's position in the sky is recorded at the same time of day throughout the year. As a consequence the gnomon draws a similar figure. Watch an animation. The red part of the analemma is used to read the time from summer solstice (June 21) to winter solstice (Dec. 22), the blue line from winter solstice to summer solstice.

 The diurnal lines are painted for (data 2002): 6/21 (summer solstice) 6/1 8/1 9/1 9/23 (vernal equinox) 10/1 11/1 12/1 and 5/1 4/1 3/20 (spring equinox) 3/1 2/1 1/1 12/22 (winter solstice)

10 units of the "Gnomon Height" menu correspond to 4 units of the grid,
e. g. "Gnomon Height 10" selected, and elevation angle of 45° the length of the shadow is 4 grid units:

The length of the gnomon is indicated by a horizontal red line:

Click into the grid to change the position of the gnomon.

Choose "Current" from the "Analemma..." menu to show the current position of the sun, the analemma for the current time and the diurnal line for the current day:

An analemma is the figure-of-eight shape that results if the Sun's position in the sky is recorded at the same time of day throughout the year. As a consequence the gnomon draws a similar figure. Watch an animation.

and animation

 Web Links The Analemma (Bob Urschel) Ausführliche astronomische und mathematische Darstellung Shadows (François Blateyron) A great sundial program for Windows (download, freeware) The Dialist's Companion DOS program that calculates a wide range of data elements of interest to dialists and others who are concerned with phenomena associated with solar time.