Solar Reflector

An Excellent Example of an Off-Axis Paraboloid

I purchased a used television satellite dish at a garage sale here in Gold Canyon. The dish was intended for use by a person who was camping, so it also came with a tripod base. I modified the tripod base to allow the dish to point higher in the sky, and I modified the dish by removing the paint, wet-sanding the surface until it was very smooth, and applying metallic mylar strips that had an adhesive backing. I also removed the microwave receiver at the focus and replaced it with a home-made wooden clamp, which I recessed behind the focus. This modified device now can efficiently concentrate the sunlight so I can use it in solar heating demonstrations. When pointed at the sun it can almost instantly burn wood or, if I previously soak the wood in water, I can generate abundant steam.

The above image shows the dish set up on its tripod on my driveway. Notice in the upside-down reflection, both my dog and I can be seen.

This is the dish before I modified it.

The shape of the satellite dish is an off-axis paraboloid (the figure you get if you rotate a parabola around its axis). For children to visualize this geometry, I have put some of the reflective mylar on the interior surface of two large bowls.

This radio telescope, which is located in Green Bank, West Virginia, has the same shape as the satellite dish: an off-axis paraboloid.

This is a closer view of the bowl representations of the paraboloid reflector. Notice how, in each, it is a small piece of a much larger bowl-like surface.

For information about the Superstition Mountain Astronomical League, see the following: supermtnastro.com and for the image repository, see the following: www.pbase.com/supermtnastro/superstition_mountain_astronomical_league