Hi I randomly came across:
Publications of the United States Naval Observatory January 1, 1900 U.S. Government Printing Office Which turns out to be a Google E-Book. It goes into some detail about just how the transit data contained in it was obtained. For the (free) price it’s worth taking a look at. Bob > On Mar 28, 2019, at 4:00 PM, Poul-Henning Kamp <p...@phk.freebsd.dk> wrote: > > -------- > In message <236772484.9174006.1553757616...@webmail.xtra.co.nz>, Bruce > Griffith > s writes: > >> 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. > > You know ... there *is* an official time-nut way to do this. > > You want is a chevron shaped 'Høg grid' because that is > objectively a very, very, very smart way of converting precise > time to precise geometry. > > I don't know of any popular explanations, but look at page 10 here: > > https://www.hs.uni-hamburg.de/DE/Ins/Bib/AG2012AK1.pdf > > The illustration on page 10 shows the original concept (from 1925!): > > By modulating the starlight with a non-uniform pattern, and sampling > the modulated light at high rate, the transit time of the star can > be determined on the order of the sampling frequency. > > Notice that the photon detector does not need high geometric resolution, > I belive Strømberg, 17 year old at the time, used a simple photo-cell > or possibly a photo-multiplier. > > Now, if you want to measure both coordinates, you move to the chevron > shaped grid illustrated on page 11, the "Høg grid". > > You still get a precise measurement of the transit along the logitudal > axis, but the width of the signal now also tells you where the star > was on the transverse axis. > > This is how the Perth 1970 catalog was made, and if not for a loose > bolt, it would have been the most precise catalog on both axis instead > of just one axis. > > The Høg grid still leaves rotation as source of error, so look at > page 2 here: > > > https://pdfs.semanticscholar.org/27f4/16df19441874fcd3b1bf52c477c889ca8045.pdf > > Imagine the light-curve you get when a star transits that slit system > in various directions, including, crucially, with a rotation[1]. > > About 12 years ago I did some ad-hoc experiements on my 5" telescope, > with various simple slit geometries, and it works a treat. > > I made the slits by taping mylar tape on a neutral filter, and cut > slits with a scalpel and a steel ruler, the detector was a large > area PIN photo-diode from the junk box and a digital oscilloscope. > > While you can prove the concept, as I did, with portable tripod > mount, to get usable data you have to bolt the telecope to a cubic > meter of concrete or bedrock. > > Poul-Henning > > [1] This becaue very important for the Hipparcos satelite which a > rocket failure left stranded in the parking orbit ... but they still > completed their science objectives. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
