[time-nuts] Setting clocks 100 years ago
jimlux
jimlux at earthlink.net
Fri Nov 5 13:46:51 UTC 2010
Hal Murray wrote:
>>> When did clocks get good enough to notice the analemma?
>
> lists at rtty.us said:
>> My guess would be the 1600's. They certainly had everything they would need
>> before 1620.
>
> What happened in 1620 to indicate that people could measure the analemma?
>
>
> One way to "discover" the analemma is to have a good clock and take a year
> long sequence of measurements of the location of the sun at noon. So how
> accurate does that clock need to be?
>
> I found a web page that said:
> For instance, on November 2nd the Sun is 16 minutes fast according to
> clock time and on February 11th it is 14 minutes slow. Mean solar time
> match on June 20th, April 14th, August 30th, and December 20th.
>
> If the clock was off by 1 second per day (number pulled out of the air), that
> would be 5 minutes per year. That wouldn't close the path cleanly, but it
> would be good enough to show the idea.
>
> When did clocks become good to 1 second per day for a year?
>
> The wikipedia article says pendulum clocks were invented in 1656. Harrison's
> H5 was good for 1/3 second per day in 1772. That probably brackets things.
>
>
> Another way would be to notice that the Earth's orbit wasn't a circle and do
> the calculations to figure out the path of the analemma. I'm not sure when
> astronomers were good enough to do that. It was probably a long time ago.
> Some of those old-timers would be right at home with a time-nuts discussion.
> One of Harrison's competitors was using Jupiter's moons as a clock, and then
> had worked out the speed of light correction for the Earth's orbit.
>
Which leads one to Kepler (Mr. orbits are ellipses), who was doing his
thing around 1600.
I would think that the analemma stuff was figured out around then.
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