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Simple Shadow Casting Sundials

Simple Shadow Casting Sundials. By Dr. Harold Williams of Montgomery College Planetarium http://montgomerycollege.edu/Departments/planet/. All Sundials. All sundials tell time by the position of the sun in the sky. Mostly they tell local apparent sun time.

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Simple Shadow Casting Sundials

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  1. Simple Shadow Casting Sundials By Dr. Harold Williams of Montgomery College Planetarium http://montgomerycollege.edu/Departments/planet/

  2. 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.

  3. 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.

  4. Equatorial Sundial with Gnome pointing toward the pole

  5. Equatorial Sundials across the planet

  6. Equatorial Sundial Summer

  7. Equatorial Sundial Winter

  8. 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 23.5o Axis Tilt 4) Earth’s Elliptical Orbit

  9. The Sundial Compared to Mean Time

  10. Some Sundial Patterns for Here • Analamic & Horizon Sundial for 39 North http://www.montgomerycollege.edu/Departments/planet/sundials/analamic_&_horizontal39.pdf • Analamic Sundial for 39 North http://www.montgomerycollege.edu/Departments/planet/sundials/ana39.pdf

  11. Some Additional Sundial Resources • North American Sundial Society http://sundials.org/ • British Sundial society http://www.sundialsoc.org.uk/ • Sundials on Mars http://www.astrobio.net/news/article625.html

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