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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