-------- 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.