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Solar Slide Rule  (Print & cut out this seasonal sun locator)

At any time during the year, this simple device can tell you how high the sun will climb in the sky for any location in the Northern Hemisphere. To build a working slide rule print or copy this sheet onto card stock and cut out the two pieces. Cut slits with a razor knife where indicated and slip the long slider piece through the slits at either end. Line up the latitude arrow to match your location (check with a state map).

When you face true south, the maximum height of the sun can be read across from the time of the year on the upper part of the slider. The winter solstice (12/21) is the shortest day of the year and when the sun will be at its lowest. From there the sun rises higher in the sky each day until it reaches the summer solstice (6/21) and starts back down. The spring and fall equinox is midpoint in this cycle.

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Solar Slide Rule Quiz

  • What is the maximum height of the sun on December 21st in your location?
  • How high does the sun get in the summer?
  • Use the slide rule to find the latitude of the Arctic Circle. What happens there on December 21st?

Notes

  • To get this to all print on one sheet, set your printer margins as tall and wide as possible
  • The solar slide rule shows only the maximum height the sun attains above the horizon at solar noon. In the morning and afternoon the sun will be lower in the sky and east and west of true south.
  • The best sites for good winter light and solar heating will have no blockage to the south higher than the sun angle on December 21st.
  • Plotting the skyline blockage on a Sun Path Chart for your location will refine this information and let you know both the times of the year and times of the day that the house will see the sun and what angle the light will be coming from.

A solar site kit with inclinometer, sun charts, a magnetic declination map (to find adjustments to true north/south) and more is available at...
www.countryplans.com

John Raabe
Country Plans LLC   (360)221-5535
5010 S. Inglewood Dr.
Langley, WA 98260, USA