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Re: clock synchronization
From: Robin Birch
Date: 2004 Feb 5, 08:57 +0000
From: Robin Birch
Date: 2004 Feb 5, 08:57 +0000
As far as I know it was established by Greenwich Observatory for their own use, then became a standard for the country which was then adopted worldwide in preference to other national observatory's standard as at the time Britain was the predominant maritime nation.
Rather than Greenwich adopt it from or for a local observatory, it was the observatory at Greenwich that set it and every one else adopted it. Originally they indicated 12:00 by dropping a signal ball on a post on the roof (it's still there and I believe they still do this). This was visible from most of the anchorages in the Thames until you got to Tower Bridge and so ships could set their clocks to 12:00.
If you get a chance go and visit Greenwich. Both the observatory and the maritime museum are very well worth the visit.
Cheers
Robin
Patrick Stanistreet <be708@LAFN.ORG>
Based upon a rather hasty bit of research concerning how it
was possible to synchronize clocks in different parts
of the world it seems that galileo, cassini and others
that I cannot credit due to ignorance came up with the
idea of creating an astronomical clock based on the
eclipses of jupiters moons. By creating accurate
tables of the times of the eclipses it was possible
to set clocks to both local time and greenwich time
to perhaps a few seconds at locations quite distant
from each other. Although not a feasible method
for ships on the ocean, they could at least compare
their clocks in ports that had observatories monitoring
jupiters moons.
The next question is say at greenwich, how was it decided
to set the local time to a particular clock time say 12:00
noon to the second? Was it a convention or was their some
method useful to any nearby observatory? ********************************************************************** This email and any attachments are confidential and intended for the addressee only. If you are not the named recipient, you must not use, disclose, reproduce, copy or distribute the contents of this communication. If you have received this in error, please contact the sender and then delete this email from your system. **********************************************************************
Rather than Greenwich adopt it from or for a local observatory, it was the observatory at Greenwich that set it and every one else adopted it. Originally they indicated 12:00 by dropping a signal ball on a post on the roof (it's still there and I believe they still do this). This was visible from most of the anchorages in the Thames until you got to Tower Bridge and so ships could set their clocks to 12:00.
If you get a chance go and visit Greenwich. Both the observatory and the maritime museum are very well worth the visit.
Cheers
Robin
Sent by: Navigation Mailing List <NAVIGATION-L@LISTSERV.WEBKAHUNA.COM> 05/02/2004 04:08 | To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM cc: Subject: clock synchronization |
Based upon a rather hasty bit of research concerning how it
was possible to synchronize clocks in different parts
of the world it seems that galileo, cassini and others
that I cannot credit due to ignorance came up with the
idea of creating an astronomical clock based on the
eclipses of jupiters moons. By creating accurate
tables of the times of the eclipses it was possible
to set clocks to both local time and greenwich time
to perhaps a few seconds at locations quite distant
from each other. Although not a feasible method
for ships on the ocean, they could at least compare
their clocks in ports that had observatories monitoring
jupiters moons.
The next question is say at greenwich, how was it decided
to set the local time to a particular clock time say 12:00
noon to the second? Was it a convention or was their some
method useful to any nearby observatory? ********************************************************************** This email and any attachments are confidential and intended for the addressee only. If you are not the named recipient, you must not use, disclose, reproduce, copy or distribute the contents of this communication. If you have received this in error, please contact the sender and then delete this email from your system. **********************************************************************
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