On Fri, 28 Nov 1997, Tom Kreyche wrote: > Seattle's long and rarely sunlit winter has begun in earnest.
Or, as a tagline on an astronomy list has it: "Where the Sun is considered a deep-sky object!" > I'm experimenting with building dials and want to test the ability of > different gnomon designs to cast shadows. Does anyone have ideas on > building simulated sources of sunlight? I'm guessing a reasonable > approximation is to simply put a bright light in a tube, and choose the > appropriate tube diameter and distance from the dial so that the angular > size appears near 32 minutes. I was a little surprised, when I worked out the diameter. I was about to suggest a bare halogen lamp bulb, as a fair approximation to a point source. But of course, you don't really *want* a point source! At 20 feet radius, you get a diameter of a hair under 2.25 inches, which is close to a reflectorized halogen lamp. Without having one handy to measure, I would say the reflector lamps are about 1.75" diameter, which works out to 16 feet from the dial. > Tom Good idea! Dave
