3 Comments

1. Nandini S says:
   December 14, 2009 at 11:34 am

   found a site on how to make them… there are like 5 or 6 different types..

   http://www.sundials.co.uk/projects.htm
2. gtarczar says:
   December 14, 2009 at 12:02 pm

   draw a circle put a stick in the middle of it, you now have an accurate sundial. to read it you must mark the point of the shadow at sun down and sun up. When the sun is directly over head it is noon. A variation of this is to use a ‘fin’ instead of a stick when the fin has no shadow it is noon
3. Philip J says:
   December 14, 2009 at 12:14 pm

   A sundial can be no more accurate than your ability to read the position of the shadow. The edge of the shadow is wider if the length is greater. Since the shadow is fuzzy and gradual, it can only be read to within a minute, regardless of the distance from the sundial’s arm to the shadow. If you need greater accuracy than that, you will need to devise a way to focus an image of the sun on the dial.

   To match the local clock time, you need to compensate for the defference between local longitude and the center of your time zone.

   Another accuracy issue is the time of year. Since the Earth is closer to the sun in December, its orbital speed is greater in December. You need to compensate for that with adjustment dials, or separate lines on the dial for different times of the year.