Free: Backyard Science

Sundials

Resources to make a quick or elaborate sundial

Sundials are a great way to:

  1. Get kids outside: "It's sunny out, go read the sundial."
  2. Learn about the geometric configuration of the Earth's rotation.
  3. Build craft project out of any material ranging from concrete and mosaic to paper.

Sundials can be configured in a number of ways, horizontal, vertical, and even cylindrical. Beyond this, there are different types of  hours that can be indicated by the dial. The 24 even hours in a day is only one system of dividing the day. I would be remiss if I didn't mention that a Google search on sundial or sundial calculator will bring up a host of great instructional sites that are well worth browsing. I'll include links to just a few that I found to be particularly easy to understand or rich in information. Did you know there was a North American Sundial Society? Take a look! They have an amazing link library with sundial resources.



Your Latitude and the Gnomon
True North versus Magnetic NorthIn order to make a basic horizontal sundial, you'll need to know your latitude. Sundials are different depending upon where you are on the surface of the planet. To find your latitude, look at a map, or Google your town's name and the word latitude. Or you can use this simple web application, just drag the red marker to your location and the latitude will show up in a window beneath the map. The latitude will be the angle of the gnomon (the raised element on the dial that casts the shadow.). The Gnomon should point to true north (not magnetic north) when you place your sundial. The offset in the US can be estimated using this map. For the rest of the world and a more accurate number in the US, try this declination tool. You'll need your latitude and longitude. Also note that the zipcode library is not complete, so it may not accept your zipcode. Lat-Long will work though. If you have a GPS or smart phone, try a compass app. Many allow you to choose between true and magnetic north. Make certain that you know which setting you are reading.


Calculate the angles of the hours
I found this page the most straight forward. Link. Enter your latitude rounded to one decimal point and the degrees are calculated for each hour's shadow. Note that this is offset by one hour during daylight savings time.

Here's another calculator, it's a little more complicated (and powerful), but generates an actual diagram of your sundial and you can generate plans for different types of dials, too.


Build your dial
Testing it in paper is a good plan. Masonry materials are cheap, easy to obtain. I recenlly had a young art student make his sundial out of a bag of quickcrete in a round form and mosaic tiles. For the gnomon, we used a piece of heavy  4ga. copper wire that can be bent to the precise angle.

 

Posted on 04/02/11 _________________________________________________________________________________________________