On Fri, Mar 04, 2005 at 10:37:17AM -0500, Lennart Sorensen wrote: > On Fri, Mar 04, 2005 at 10:24:30AM +0100, Martin Dickopp wrote: > > Both of you are joking, I take it. But just in case someone is tempted > > to take this suggestion serious: The sun position does *not* peak at > > 12:00 "winter time" or 13:00 summer time. The deviation can be an hour > > or more, and furthermore it changes every day. > > The sun does peak the same time every day, but it's only at noon exactly > if you are in the right place on the planet (for your time zone). If > you are east or west of that the time will be off a bit, but it will > still be the same every day. Actually, that's not true. It varies quite a bit, as Martin said. Take a look at the Equation of Time. The variation isn't anything like as much as the hour that Martin said -- it's about +/- 15 minutes over the year. The reason it varies is (IIRC) to do with the fact that the Earth's orbit isn't circular. > The earth is pretty consistent in rotating > at a steady speed. Otherwise sundials wouldn't work very well. Basic sundials such as those seen in many people's gardens *don't* work very well, for the very reason given above (and the fact that they're rarely set up properly). A good sundial installation will always have some method of correcting for the current position in the equation of time, usually either by having a date-driven graticule on the plate, or by having a suitably-shaped gnomon. I've also seen sundials with the equation of time inscribed in the plate, so that you can do the correction manually. Hugo.  http://www.sundials.co.uk/equation.htm -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 1C335860 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- I always felt that as a C programmer, I --- was becoming typecast.
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