Of course the time scale will be much shorter for a star occulted by an edge etc on Earth. The longer time scale for a lunar occultation is due to the slower relative angular motion of the moon with respect to the star than the motion of the Earth with respect to a star. Bruce > On 27 March 2019 at 17:41 Bruce Griffiths <[email protected]> wrote: > > > These light curves for a star being occulted by the moon should give some > idea of the effects of diffraction: > > http://tdc-www.harvard.edu/occultations/moon/vb141occa.html > > Bruce > > On 27 March 2019 at 15:48 Tom Van Baak <[email protected]> wrote: > > > > > > BobH wrote: > > >> This would be an excellent project for time-nuts to verify. First, a > > >> better explanation of John Harrison’s method is in order. A vertical > > >> window edge is not sufficient - a second vertical reference at a > > >> distance is required - Harrison used a chimney on a neighbor's house. > > > > Agreed! The project is the perfect intersection of amateur astronomy and > > amateur timekeeping. Surely, a couple of people on the list could 1) > > attempt to verify the Harrison method, and 2) determine what the limits of > > its accuracy are, say, with little effort vs. with hard work vs. with > > extreme dedication. > > > > JimL wrote: > > > To get 1 second accuracy, you need 360/86400 = 0.004 degree > > > measurements. That's 0.073 milliradian - 1 cm at 140 meter distance. > > > > > > I'm not sure an "edge" is sharp enough (diffraction, etc.), although > > > your eye is pretty good at "deconvolving" the linear equivalent of an > > > Airy disk/rings. > > > > Keep in mind too that one can take more than one star reading per night. > > Any identifiable star that crosses your edge is a recordable timing event > > that evening. So, in theory, if you measure N stars you get sqrt(N) > > improvement in accuracy per day. > > > > I want to encourage anyone to study the problem and help solve the riddle, > > either by uncovering existing professional or amateur literature or by > > actually trying this at home. It boils down to how accurately can you > > measure earth rotation using the Harrison method. > > > > To put this in time nuts context, precision timekeeping prior to the middle > > of the 20th century was always a form of "Earth Disciplined Oscillator". > > Not unlike a GPSDO, your observatory's pendulum clock kept accurate time > > short-term and star tracking (earth rotation) kept accurate time long-term. > > The ADEV's crossed just like a GPSDO. > > > > The short-term ADEV of a really good pendulum clock is here: > > > > http://leapsecond.com/pend/shortt/ > > > > The long-term ADEV of earth rotation is here: > > > > http://leapsecond.com/museum/earth/ > > > > So the performance of a DIY earth disciplined oscillator would be a > > combination of the two. > > > > /tvb > > > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there.
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