Hi I think the key point is that they are still using a gizmo made in the 1800's and it works "good enough". There are certainly better ways you could set it up today, but they use what they have.
Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Attila Kinali Sent: Monday, January 23, 2012 11:57 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Determination of the placement of the first pps On Mon, 23 Jan 2012 08:43:01 -0800 Chris Albertson <[email protected]> wrote: > > It's a transit telescope (one that looks up at the local meridian) but > they don't use the sun. It looks at every start that passes in front > of it, thousands of them every night. Then they reduce the data by > knowing the exact location of every star and the time is pasted > directly overhead. This way they get thousands of measurements every > day. If you use the Sun you get only one per day. Not to mention the solar noon varies by +/- 15min over the year (don't ask me how this is called...old knowledge from my high school days) > A transit solar scope would be a fun Time Nut project. I think a > primitive one would be a photo cell and a length of wire. Measure the > time when the shadow of the wire sweeps across the cell. The trouble > is that with only one measurements per day it would time years to > build up uSec level data. Even if you placed the cell behind a pin > hold mask and used a fine piano wire, shades and baffles and so on. Why not use a real telescope with a CCD and get more reliable data? A friend of mine is into hobby astronomy and uses special type CCDs for it (ie not even the hobbist look directly into the telescope anymore). I guess it shouldn't be too hard to rig up some gear, a PC that collects the pictures at precise instances and calculates the ephemeris time to UTC/GPS difference. The only issue is that you'd need to put that telescope somewhere with little light polution, otherwise you'll only get the brightest stars. Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
