[time-nuts] zero crossing of venus

Jim Lux jimlux at earthlink.net
Wed Jun 6 14:39:03 UTC 2012


On 6/6/12 7:02 AM, Mike S wrote:
> On 6/6/2012 9:09 AM, Jim Lux wrote:
>
>> does anyone have a reference to the math and process used to measure
>> distance from earth to sun using transit of venus?
>
> http://transitofvenus.nl/wp/getting-involved/measure-the-suns-distance/
>


Of course, back in the 1700s, they didn't have nice iPhone apps to give 
good time hacks..

I see that Halley's scheme relied on measuring the length of the chord 
of the transit, which could be done geometrically (at least from the 
drawing, it looks that way), without needing time involved.
http://www.transitofvenus.nl/halleysmethod.pdf  seems to say that a 
precision of around 1 second for the duration between contacts would do. 
  (of course, here in southern California, we couldn't do it, because 
the sun set before 3rd contact)


Delisle's technique seems to require synchronized clocks.  How well 
synchronized?

A good math treatment of the technique would be nice to find, then one 
could take known clock and measurement accuracy and figure this kind of 
thing out. I think this has more of the info
http://www.venus2012.de/venusprojects/contacttimes/basicidea/basicideatimes.php
but I'm still looking through it.

I'm also interested in how did they get their "absolute time" hack for 
the Delisle technique.

It's an astronomical measurement, so maybe the lunar distances or Jovian 
moons approaches would work, but then you have to have a stable enough 
clock to last from night until day.



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