[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.




More information about the Time-nuts_lists.febo.com mailing list