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Sidereal Sundial Applet
This horizontal sundial is showing the local sidereal time
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Check your time zone offset and the local time. |
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Click the
applet first! |
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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 ! |
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Press shift key and click into the sundial area to change the gnomon position. |
How to get this applet for offline use
More of my sundials:
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Sidereal
time is defined as the hour angle of the vernal equinox.
(Local)
Sidereal Time = (Local) Hour Angle + Right Ascension θ = τ + α.
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 local siderel time.
Any point of
the horizontal plane is crossed by two sidereal hour
lines, one for the first half of the year, and one for the second:
 Berlin: Feb 24 at 10:51 CET: Local Sidereal time is 21:00  Berlin: Oct 17 at 11:21 CEST: Local Sidereal time is 12:00
On
the
day of the vernal equinox, at local noon, the local sidereal time
is 00:00.
On
the
day of the autumnal equinox, at local noon, the local sidereal time
is 12:00. The
grid
size
is
2.5
m (independent of the gnomon height).
Choose
"Write Data" from the "Details" menu:
 Choose
"Write Sidereal Time Month" or "Write Sidereal
Time Day" from the "Details" menu:
 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.
Please visit my pages: and animation
Please visit my
GeoAstro Applet Collection Last Modified: 2010, Aug 17 © 2008-2010 Juergen Giesen
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Click into the grid (shift key held down) to change the
position of the gnomon. 
