Design an Earth Dial For Your Latitude

1. Design an Earth DialFor Your Latitude North American Sundial Society Created by: R.L. Kellogg rkellogg@comcast.net Feb 2004 This is an unusual power point presentation. By enabling the Visual Basic macros, you can create your own Two Worlds – One Sun Earth Dial. First, check your power point security setting: Click on “Tools” , “Macro”, “Security…”. Set the security level to “medium”. To be sure the macros are safe, choose the “Alt + F11” keys to review the Visual Basic code (Modules, Module1). Exit the Visual Basic code and Power Point program. Restart power point and respond to the dialog box “enable macros”. This will be the normal startup to activate the program features. There is no need to view the Visual Basic code when the power point program is used for sundial construction. 1. Start power point (in “medium” security mode) and “enable macros” 2. On the next slide, (the sundial construction slide) enter your city or town name by changing the text of “Your City Name”. Replace, but do not delete or 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 to the bottom of the slide. 3. At the top of power point, select “slide show” and “view show”. 4. Go to the dial construction slide. 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 Earth Dial. The dial is based on Woody Sullivan’s Earth Dial, found at http://planetary.org/mars/earthdial_instructions.html. This draws a slightly smaller dial that fits on one piece of paper. 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. Exit the slide show. You may add additional text or shapes to the sundial. When finished, print out the Earth Dial. 9. Cut out the Earth Dial and glue it to a piece of wood or stiff cardboard. Varnish it for weatherproofing. 10. You need to construct a gnomon (shadow caster). Use a wood dowel and ball the same size as drawn to the left of the dial. Push the dowel into the ball and glue the dowel vertically on the Earth Dial center circle. 11. Align the 12 o’clock line toward north. If you are in the southern hemisphere, align the 12 o’clock line toward south. Your Earth Dial will now tell local apparent solar time. It may differ from actual clock time due to your longitude and due to the sun’s slight irregular motion throughout the year (called the Equation of Time, where the apparent sun “runs” fast or slow of the mean solar time by about 15 minutes maximum. The Equation of Time is found on slide 3 of this presentation.

2. H T 2 R 0 A 0 E 4 12 11 1 10 2 9 3 8 4 7 5 Gnomon Shape Luqa, Malta Latitude: 35.8 Degrees T N W U O S Draw Dial W E O N 36 R O L D - S Clear

3. The Sundial Compared to Mean Time