Sundial at Aberdour Castle
April 26, 2010
Before the invention of clocks and watches, the only way to tell the time of day was by the position of the Sun in the sky. The ancient Egyptians used the shadows cast by obelisks as a simple method of distinguishing forenoon from afternoon. Over the centuries this method was developed and refined into the sundials which became commonplace from the 1500s-1800s.
This sundial on the wall of Aberdour Castle in Fife, Scotland, has been telling the time on sunny days for over 300 years. The central blade, or gnomon, casts a shadow from the moment the Sun rises. As noon approaches, the size of this shadow becomes shorter and shorter until it disappears when the Sun is high in the sky. As the day wears on, the shadow lengthens once again. The gnomon has to be triangular in shape and set parallel to the Earth’s axis for the sundial to be accurate all year round. Unlike a conventional clock, sundials in the Northern Hemisphere are numbered anticlockwise as the shadow cast by the rising Sun falls on the left of the south-facing sundial and works its way round to the right side. Sundials in the Southern Hemisphere face north and are numbered clockwise.
In the days when people rarely traveled any distance, the sundial was the perfect tool for accurate timekeeping as long as the Sun was shining. Of course it only gives the time locally. Sundials further east or west of a given location will read a slightly different time, and this difference increases with distance. The invention of rail travel required the standardization of time so that people knew exactly when to catch trains and what time they would arrive at their destination. This led to the adoption of Greenwich Mean Time (GMT), measured from the Greenwich Meridian (0 degrees longitude), as the standard for British time. Photo taken on April 11, 2010 at 3:40 p.m. local British Summer Time or 14:40 GMT.
Photo details: Camera: PENTAX *ist DL2; Image Date; Focal Length: 55mm (35mm equivalent: 82mm); Aperture: f/9.5; Exposure Time: 0.0029 s (1/350); ISO equiv: 200