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Re: Sundials

Hugo Mills <hugo-64@carfax.org.uk> writes:

> 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[1]. The variation isn't
> anything like as much as the hour that Martin said -- it's about +/-
> 15 minutes over the year.

Just for the record, I didn't say that the equation of time is up to one
hour, but that the discrepancy between 12:00 (or 13:00 summer time) and
the peak position of the sun can be one hour or more. This discrepancy
is mostly due to the constant difference between local time (i.e. /mean/
solar time) and zone time.


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