[time-nuts] zero crossing of venus

[jmfranke]

Jim,

Look at:

http://www.venus2012.de/venusprojects/photography/basicideas/basicideas.php

http://www.didaktik.physik.uni-due.de/~backhaus/Venusproject/mercury2003.htm

http://www.exploratorium.edu/venus/question4b.html

John  WA4WDL

--------------------------------------------------
From: "Jim Lux" <jimlux at earthlink.net>
Sent: Wednesday, June 06, 2012 9:09 AM
To: <time-nuts at febo.com>
Subject: Re: [time-nuts] zero crossing of venus

> On 6/5/12 5:20 PM, Tom Van Baak wrote:
>> Attached are two snapshots of a NASA live feed -- an interesting reminder 
>> about the difficulty measuring timing signals with great precision.
>>
>> When you look closely, the leading edge of the sun is rather ill-defined, 
>> not unlike many 1PPS pulses. I suppose with enough photos, modeling, and 
>> image processing one could pinpoint when the transit (zero crossing) 
>> really occurs to great precision. Does anyone know more details how this 
>> is done? Is the state-of-the-art at the millisecond level? microsecond? 
>> nanosecond?
>>
>> Thanks,
>> /tvb
>>
>>
>
> Speaking of this..
> does anyone have a reference to the math and process used to measure 
> distance from earth to sun using transit of venus? I assume it makes use 
> of some astronomical time measure to determine when Venus enters and 
> leaves from different viewing places. but that would require a clock that 
> can time from night (when you get an astronomical measurement) to day 
> reasonably accurately.  Or, do you measure the position of the sun in the 
> sky (something that's fairly easy to do)
>
> But maybe not.. maybe it's more about "where it enters and leaves the 
> solar disk" (in an angular sense, i.e. what's the length of the chord) 
> positionally, in which case the time is less important.
>
>
>
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