Design a Gnomonic Sundial For Your Latitude North American Sundial Society Created by: R.L. Kellogg Sept This is an unusual power point presentation. By enabling the Visual Basic macros, you can create your own Gnomonic Sundial. The Visual Basic macros have been locked to prevent tampering. If you choose to use this presentation: First, check your power point security setting: Click on “Tools”, “Macro”, “Security…”. Set the security level to “medium”. Exit the Visual Basic code and Power Point program, restart the power point and respond to the dialog box “enable macros”. This will be the normal startup to activate the program features. You are prevented from seeing the Visual Basic code, but if you would like a copy, please Robert Kellogg at the above address. 1. Start power point (in “medium” security mode) and “enable macros” 2. On the next viewgraph, the sundial construction slide, enter your school name in the text box. Do not delete this box nor move it “in front” or “in back” of any other object. If you do not care for a name on your sundial, move the text box to the bottom of the slide. 3. At the top of power point, select “slide show” and “view show”. 4. Go to the next slide for dial construction. Click the up and down arrows to select your latitude (+ for north, - for south). 5. Click the “Draw Dial” button. Power Point will draw your Gnomonic 6. You may select other latitudes and “Draw Dial” again and again. It clears the display before drawing. 7. You may clear the dial and gnomon by selecting “Clear” 8. End the slide show and print out the Gnomonic Sundial slide. 9. Cut out and fold the Gnomon to cast the shadow. The height and position of the Gnomon is very important. The one you cut out is made for your latitude. Glue it onto the dial where indicated. 10. Place the Sundial in a sunny spot with the 12 o’clock hour of the dial pointed North (South for Southern Hemisphere). Read the time. This is “local solar time” and may differ from your clock “standard time”. You can use the Equation of Time graph to correct the sundial to standard time. Variability in the earth’s orbit around the sun, the earth’s axis tilt, and the sundial location away from the longitude of the time zone may cause the Sundial to be up to 45 minutes off.

Draw Dial Clear 38 North American Sundial Society Tab jan feb mar apr may jun jul aug sep oct nov dec 9AM 10AM 11AM 12PM 1PM 2PM 3PM E N W S Cut Dial Out Along Line Cut Out Gnomon Dotted Edge Toward 12PM Tab Lat = 38

The Sundial Compared to Mean Time