Sundial

This simulation shows a horizontal sundial and the shadow of its gnomon sweeping across the plate as the Sun moves. Sliders set the latitude between 10 and 65 degrees north, the month and the solar time, and the day can run automatically. Readouts give solar time, shadow angle, Sun elevation and Sun declination. Students notice that the hour lines are not evenly spaced and that the gnomon is tilted by the latitude. It links history, geography and mathematics, and shows how people told time before clocks.

• Turn Auto run on and watch the shadow cross the dial from morning to evening.
• Drag Solar time to 12 and check where the shadow falls on the noon line.
• Change Latitude and see how the gnomon tilt and the hour line spacing change.
• Compare Sun elevation at noon in Month 6 and Month 12.
• Read the Shadow angle each hour and check it is not the same every hour.

1. 1Explain how a sundial uses the shadow of a gnomon to show the time.
2. 2Describe why the gnomon is tilted at an angle equal to the latitude.
3. 3Compare the Sun height at noon in summer and in winter.
4. 4Recognize that the hour lines on a flat dial are not evenly spaced.

Questions teachers ask