Nice idea, John! Moving the laser pointer a precise distance horizontally isn't really necessary, nor exactly what you want. I think the requirement would be to move the pointer along whatever axes you need to, but without changing it's angular orientation. That way, you move from the pointer projecting one ray across the gnomon onto the dial plate, to a parallel ray through the "pinhole" mirror...
Using this projection method, you could easily and quickly test where various lines would fit on the ceiling, and adjust the mirror to get the placement you want. Of course, any kind of "master" dial can be used, of any convenient size! Use one of the fine pieces of software distributed through NASS, make a paper horizontal dial with a long needle for style and nodus, and you can transfer as many points as you wish, to the ceiling, walls, whatever. Compare to Robert Terwilliger's Laser Trigon, and his Shadow Garden: http://www.shadow.net/~bobt/garden/garden.htm Dave 37.29N 121.97W On Mon, 31 Dec 2001, J Lynes wrote: > Here's an alternative approach, which would work best with two people: > Set up a simple horizontal sundial, with declination lines, correctly > oriented, beside the mirror, say a foot to one side. > Using a laser pointer, or just a bare low-voltage filament lamp, cast a > shadow of the gnomon onto the sundial scale at some chosen hour and > declination. > Move the laser pointer exactly one foot sideways to illuminate the centre of > the mirror. > Mark the position of the spot of light reflected onto the ceiling. This is > the point on the ceiling sundial for the chosen hour and declination. > Repeat for other hours and declinations. > Note that this does not assume that the mirror is horizontal. > Obviously the method could be simplified if declination lines are not wanted > on the ceiling. > Happy New Year! > John Lynes >
