Brooke Yes but the accuracy would suffer due to observer related effects. However when used with a CCD camera or equivalent the accuracy should improve somewhat much as adding a TV camera to a transit circle improved its accuracy. I had a personal tour of the USNO setup on Black- Birch/Altimarloch during their southern hemisphere campaign during the 1980's.
Bruce > On 27 March 2019 at 20:39 Brooke Clarke <[email protected]> wrote: > > > Hi Bruce: > > Would the David White 60 Degree Pendulum Astrolabe also work? > https://prc68.com/I/PendulumAstrolabe.shtml > > -- > Have Fun, > > Brooke Clarke > https://www.PRC68.com > http://www.end2partygovernment.com/2012Issues.html > axioms: > 1. The extent to which you can fix or improve something will be limited by > how well you understand how it works. > 2. Everybody, with no exceptions, holds false beliefs. > > -------- Original Message -------- > > The Danjon impersonal astrolabe is perhaps better suited to accurate > > measurements: > > https://www.nzmuseums.co.nz/collections/3267/objects/3380/astrolabe > > > > 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. > > > > > _______________________________________________ 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.
