Materials needed: face plate (made in Sundial part I), protractor, glue, BBQ skewer, cardboard scrap, cardboard rectangle large enough to hold sundial/BBQ skewer arrangement
Now that you have made the face of the sundial, you need to set it. That requires two pieces of knowledge about where you live. In this brief lesson, we will discuss your latitude.
You can find your latitude by googling “latitude your town“, or you can check a map. The face plate of your sundial must be angled to that same angle. There are a number of interesting ways to make this happen depending on your sundial design. For instance, I have made jiffy sundials from folded postcards of the place I’m visiting. Here is one easy way to use your latitude angle:
- Make a hole in the very center of your sundial face with a thumbtack.
- Insert a BBQ skewer, having a tight friction fit. The skewer will be your gnomon. The gnomon casts the shadow. “Gnomon” is Greek meaning one who knows.
- Prop the other end of the BBQ skewer against a triangle which you cut from cardboard. The triangle will be a right triangle (one angle is 90 degrees) with your latitude angle positioned as shown in the drawing below. Make sure you have the triangle positioned correctly. Apply a strip of glue to the triangle and glue it to the skewer. Optional: Leave a small extending point below the triangle. You can use this small point to stick the skewer into a slab of cardboard as a base for your sundial and move it around more easily.
- For example, my latitude in San Francisco is 38 degrees. See the drawing to look at the correct angle position.
- The friction fit of the skewer in the face plate will hold the face plate at the correct angle. The friction fit will also hold the skewer at a 90 degree angle to the face place – which is necessary for correct shadow casting. You can double-check that 90 degree angle by putting a square piece of cardboard under the gnomon.
There is one more step: finding true north. That will be addressed in the next lesson. Apologies for the simple sketch; I will replace it later with a photo.