jlynes
Wed, 11 Aug 2010 12:05:56 -0700
When a mirrored sphere is viewed or photographed from a sufficient distance, the size of the distorted image of objects reflected will be proportional to the solid angle that they subtend at the centre of the sphere. In terms of cartography, the reflection is an "equal-area projection". This property comes in handy for lighting engineers, who use equal-area projections for publishing the intensity distributions of street lights and floodlights. To see what light strikes surrounding surfaces, one simply superimposes the equal-area intensity plot on the equal-solid-angle projection of the surroundings.
If a mirrored sphere is viewed or photographed, horizontally or vertically, in the position to be occupied by a proposed sundial, it is a simple matter to work out the azimuth and altitude of surrounding obstructions to sunlight. This might be useful in comparing alternative sites for a new sundial. But I doubt if that argument is going to sell many mirrored spheres! John Lynes ________________________________ From: Mike Cowham <m...@brownsover.orangehome.co.uk> To: sund...@rrz.uni-koeln.de Sent: Wed, 11 August, 2010 13:26:49 Subject: Stainless Steel Spheres Dear Dialling Friends, I have just visited our local garden centre and they had a large quantity of 'Gazing Balls' on sale. These are 8" / 20cm diameter stainless steel spheres with no obvious seams or stalks, and with a mirror finish. They MUST be of use to many of you for dialling, for making globes or for ????? They are made by Gardman and they were selling two for £9.99, quite a bargain. If any of you have ideas how these can be used in dialling, I will be pleased to hear from you. If you make something from them, I am sure that we would all like to hear. Have fun, Mike Cowham.
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