Simple Shadow Casting Sundials By Dr. Harold Williams of Montgomery College Planetarium

All Sundials All sundials tell time by the position of the sun in the sky. Mostly they tell local apparent sun time. At sunrise the sun is just coming up on the horizon. At midday, noon, the sun is crossing the meridian, the line that runs from north to south through the zeinth, (the point over head). At sunset the sun is just going down on the horizon.

Most Sundials Most sundials work by casting shadows with a “gnome,” shadow caster. The shadow is projected on a surface that is a dial face telling you the time.

Equatorial Sundial with Gnome pointing toward the pole

Equatorial Sundials across the planet

Equatorial Sundial Summer

Equatorial Sundial Winter

The Sun reaches its Zenith (Peak) at High Noon… NOT! The Sun Peaks in Takoma Park at 12:16 PM EST on March 18, 2006 Corrections: 1) Daylight Savings 2) Time Zones 3) Earth’s 23.5 o Axis Tilt 4) Earth’s Elliptical Orbit

The Sundial Compared to Mean Time

Some Sundial Patterns for Here Analamic & Horizon Sundial for 39 North rtments/planet/sundials/analamic_&_horiz ontal39.pdf rtments/planet/sundials/analamic_&_horiz ontal39.pdf Analamic Sundial for 39 North rtments/planet/sundials/ana39.pdf rtments/planet/sundials/ana39.pdf

Some Additional Sundial Resources North American Sundial Society British Sundial society Sundials on Mars ml ml