[time-nuts] Determination of the placement of the first pps
lists at rtty.us
Mon Jan 23 12:07:42 EST 2012
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.
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] 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 <albertson.chris at gmail.com> 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
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
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