Accurate Diaists ,
Maybe this is off subject... but, is it possible to build a "dithered" gnomon so that it could minimize the prenumba (<- spelling?). Or some other shape that produces a more finite edge. Best regards, Mike ----- Original Message ----- From: Edley McKnight <[EMAIL PROTECTED]> To: walter.jonckheere <[EMAIL PROTECTED]> Cc: <[email protected]> Sent: Saturday, December 22, 2001 12:43 PM Subject: Accuracy again > Dear Walter and Membership, > > Accuracy again. > > Increasing the surface movement of the shadow or spot of light by the > means of optical levers allows very fine time measurements. > > In our mind's eye we can fix a small mirror so that it reflects a > small part of the sun's image far out into space. In seconds the > reflected image can move from star to star. At that vast distance > the surface rate of movement of the reflection is thousands of > lightyears per second! > > In general when we magnify the sun's image size on a surface we > increase the rate of movement of the image on that surface. If we > choose to only reflect a very small portion of that image, it still > moves very fast, being a sensitive indicator of the angle of the > sun's rays. Thus, if the mirror were about 300 meters away from the > surface, the spot reflection would move about 2.2 centimeters per > second if the path of the refection were in the equatorial plane. > > Of course that distance could be folded by reflecting from optically > flat first surface mirrors so that a smaller device could measure > small increments of time. > > The larger sundials use an optical lever with it's fulcrum at the tip > of the gnomon, thus increasing the rate of surface movement of the > shadow. A small opening, acting as a pinhole lens, can focus a spot > of light and sharpen the image. > > Enjoy the Light! > > Edley McKnight > > [43.126N 123.357W] >
