Capricorn: Dec.22-Jan.29 The Sundial Primer
created by Carl Sabanski
Capricorn: Dec.22-Jan.29

Mr. Sun The Sundial Primer Index "Sunny Day U" Index Mr. Sun

"SUNNY DAY U"


Globe Sundial Kit

Globe Sundial: (or spherical dial): a class of dial in which the "dial plate" is a globe or sphere, usually set with its axis parallel to the Earth's polar axis and often with the observer's position at the top. The gnomon is in the form of a thin semi-circular vane, which can swivel around the globe about its axis. In use, the vane is rotated until the shadow is minimised and the time read from an equiangular scale around the equator. It indicates the meridian of longitude where it is currently noon.


The globe sundial presented here is an equatorial sundial and will work anywhere in the world. It is a challenge to make but not impossible to do. The kit is based on a 6 inch diameter styrofoam ball used in floral arrangements or crafts. The ball is not very expensive.

Figure 1 shows a portion of the Kit that you will use to make your own globe sundial.

Figure 1: Globe Sundial Kit

Figure 1: Globe Sundial Kit (CAD)

The kit can be used to make a globe sundial for either the Northern or Southern Hemisphere. All the structural parts of the sundial were made from 1/2 inch rigid styrofoam board. To give the edges a clean finish you can use metal foil duct tape.  The tape has an adhesive backing and bonds well to the styrofoam. To glue all the parts together I recommend you use a silicone rubber adhesive called "RTV". It provides an excellent bond and does not warp. The glues I used did not bond very well to the ball.

I soon discovered that a 6" styrofoam ball is not really 6 inches in diameter. The one I used was about 5-27/32". Due to the variation in the diameter of the ball you can download a PDF of the "Globe Sundial Kit" in diameters ranging from 5-3/4" to 6-1/16" in increments of 1/32".

BALL DIAMETER
6"
5-27/32"
...more to come

The most difficult part is establishing the equatorial line on the ball. I taped the hour bands together and used the long hour line sections to help. There may be some other better ways. Dry fit the hour bands to get an idea of how you will put the sundial together and how well the fit is. 

When you have completed the sundial all you have to do is set up and it will tell you solar time. Just rotate the globe until the "Latitude Pointer" is aligned to the correct latitude. A vernier scale is used to set the angle of the globe to the nearest 1/4 for a latitude scale spaced at intervals of 1. To learn more about the vernier scale visit the "Standard Time Equatorial Sundial Kit" page. To read the time just rotate the vane until its shadow on the globe is as thin as possible.

Here's what the sundial will look like once you have finished making it. This one is located in the Northern Hemisphere and positioned for a latitude of 50.

Globe Sundial - Front View Globe Sundial - Rear View

Happy Dialling!