Make your own Equatorial sundial:

Materials required: A pencil, protractor, compass and a straight edge.

The equatorial dial is the easiest to lay out, the gnomon is a rod that runs through and perpendicular to the dial face. Since the gnomon must point to the North Celestial Pole the face of the dial is ,therefore, parallel to the Equator. This is called an Equatorial Dial.

Draw a circle and divide it into 15 degree pieces (use the protractor).

Why 15 degrees? One day is 24 hours, or the amount of time it take for "the sun to go around the earth". So in 24 hours the sun "moves" through 360 degrees (recall that there are 360 degrees in a circle). Therefore to find how many degrees are in 1 hour we divide 360 by 24. 360/24=15 degrees, this is called the hour angle of the sun.


Number the lines as shown, this is the upper dial.

Now turn the the dial over and draw the same lines on the other side. Number these counterclockwise.


Now run a rod (the gnomon) through the center of the dial making sure that the face of the dial is perpendicular to the gnomon. Set the dial so that the gnomon is pointing to true north and is elevated from the vertical by latitude (as measured in degrees) and the 12:00 hour line is pointing toward the ground.


Why the two dial faces?

Since the sun is north of the Equator half the year and south of the Equator the other half each dial will only receive sunlight half the year.

The upper dial receives sunlight from March 21 (the Spring or Vernal Equinox) through September 21 (the Fall or Autumnal Equinox). Therefore the upper dial gets sun from the first day of spring through the summer and stops in the fall.

The lower dial receives sunlight from September 21 (the Fall or Autumnal Equinox) through March 21 (the Spring or Vernal Equinox). Therefore the lower dial gets sun from the first day of fall through the winter and stops in the spring.

Make your own Horizontal Sundial.

Make your own Vertical Sundial.


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Changes last made on: January 20, 1998
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