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G4EBT > TIME 23.10.06 15:21l 111 Lines 4849 Bytes #999 (0) @ WW
BID : DA3188G4EBT
Read: GUEST
Subj: Re: GMT, G0TEZ
Path: ON0AR<GB7SYP<GB7LGS<GB7ESX<GB7FCR
Sent: 061023/1418Z @:GB7FCR.#16.GBR.EU #:1431 [Blackpool] FBB-7.03a $:DA3188G4E
From: G4EBT@GB7FCR.#16.GBR.EU
To : TIME@WW
Ian, G0TEZ wrote:
(In connection with BCE/CE v BC/AD):
>A bit like GMT really.
True.
The international standard is coordinated universal time, abbreviated UTC,
formerly known as Greenwich mean time (GMT). Other terms used to refer to
it include "Zulu time" (after the "Z" often used after UTC times),
"universal time," and "world time."
UTC is now used by international shortwave broadcasters in broadcast and
programme schedules, by ham radio operators, shortwave listeners, the
military, and utility radio services.
Greenwich Mean Time was based upon the time at the zero degree meridian
that crossed through Greenwich, England. GMT became a world time and date
standard because it was used by Britain's Royal Navy and merchant fleet
during the nineteenth century.
UTC uses precise atomic clocks, shortwave time signals, and satellites to
ensure that UTC remains a reliable, accurate standard for scientific and
navigational purposes.
The Royal Observatory at Greenwich was founded in 1675 (AD/CE!) to observe
and record the movement of heavenly bodies in an attempt to solve the
longitude problem by the lunar distance method.
The observatory building was designed by Wren and was built on the highest
ground in Greenwich Park with rooms for the appointed astronomer, John
Flamsteed. He worked on the project for over 40 years, and his star
catalogue was published posthumously in 1725.
I guess many will be familiar with the importance to mariners of
accurately calculating longitude. Ships at sea could measure latitude by
the sun or stars but to determine longitude required time comparison, with
an hour's time difference equal to 15 degrees of longitude.
One degree of longitude = four minutes of time the world over, but in
terms of distance, one degree shrinks from 68 miles at the equator, to
virtually nothing at the poles. One hour = 15 degrees. (360/24).
Clocks back then used pendulums - useless at sea. Even if time could be
measured to an accuracy of four minutes it meant an error of +/- 68 miles
at the equator. That was well over the horizon in both directions, s ships
often got lost. (They could of course check the time with the sun at its
highest point at noon).
The loss of 4 warships and 2000 men under the command of Admiral Sir
Cloudsley Shovell off the Scilly Isles in 1707 prompted the passing of the
Longitude Act in 1714 offering a prize of œ20,000 - a huge amount back
then, for a 'practicable & useful' solution. A sum of œ8,750 was
eventually and reluctantly awarded to Yorkshire clockmaker, John Harrison
who spent 40 years developing his marine chronometer.
Harrison's clocks are on display at the Royal Observatory at Greenwich,
( free admission!) - well worth a visit. The intricacy of his designs and
quality of workmanship is superb.
Harrison lived just a few miles from here, at Barrow on Humber on the
south bank of the river Humber. He made a large clock in wood which is
still keeping good time 20 years later, in a clock tower at Brocklesby
Park,
near Grimsby.
Astronomers looked down on clockmakers, calling them "mechanics" in a
derisory way. They thought the problem of calculating longitude would
only be solved by astronomical means. It's ironic that nowadays, the
cheapest wrist watch using a crystal timebase would do the job nicely.
A Meridian is just an abstract starting point so ships would use their
home port and observatories would set on their own position. Greenwich
actually has 4 meridians as successive astronomers - Flamsteed, Halley,
Bradley & Airy worked from different points with new equipment.
The choice of the Greenwich Meridian wasn't just a matter of "Britain
Rules the Waves". It was decided in 1884 at a conference in Washington DC
by representatives from 25 countries.
They voted to make Greenwich the Prime Meridian of the world as the
Nautical Almanacs produced by Nevil Maskelyne, the fifth Astronomer Royal,
were the most comprehensive and widely used at that time. (The French
however retained their Paris Observatory Meridian until 1911).
The story of John Harrison and his solution to the longitude problem was
the subject of Dava Sobel's excellent book 'Longitude'. This was made into
an excellent TV programme too, with Michael Gambon and Jeremy Irons, which
is still available on video and DVD.
I seem to recall that a few years ago, there was a "Special Event"
activity day for amateur radio stations up and down the UK which were
located on the Meridian. I don't know if special callsigns were issued
though - I don't take any interest in on-air activity.
73 - David, G4EBT @ GB7FCR
British Vintage Wireless Society Member
G-QRP Club Member, No: 1339
QTH: Cottingham, East Yorkshire.
Message timed: 13:32 on 2006-Oct-23
Message sent using WinPack-Telnet V6.70
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