THE WILDS sundial
"Blessed too is he who learned to know the Gods of the Wilds"
The Wilds horizontal sundial is reading true local Solar Time. This varies from Mean Time or South African Standard Time (SAST) in 2 ways:
Firstly our time zone is based on the 30 east meridian which is 2 hours ahead of Greenwich Mean Time. Since The Wilds is at 28 east there is a longitude correction of plus 8 minutes since the solar time at The Wilds is 2 behind that at the 30 meridian because the Earth spins anti-clockwise. This 8 minutes is a constant and must be added to all readings from the dial.
Secondly the Earth's orbit around the sun is elliptic and thus there is a daily variation to Solar Time experienced on Earth. This variation between Solar Time and Mean Time is called the Equation of Time. A graph of the variations for each day of the year is reproduced below. Simply apply the correction for the day to any reading from the dial:
Any correctly orientated sundial will also tell the time by moonlight. First establish the days before or after full moon. Most diaries and calendars will give this information. Then apply the adjustment given. However longitude correction, then the Equation of Time and then days before or after full Moon may all be a bit much for Moonlight Lovers on Valentine's Night!
Malcolm Barnfield
www.sundials.co.za
The sundial was made by Dave Baguley with sandstone from Naboomspruit, Limpopo and set-up by Malcolm Barnfield on Mothers Day, Sunday May 8, 2005.
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