[time-nuts] Setting clocks 100 years ago
Rob Kimberley
rk at timing-consultants.com
Fri Nov 5 08:31:23 UTC 2010
I thought the ball dropped at noon. Perhaps you were there in the summer,
and they had advanced 1 hour for summertime (daylight savings).
Rob K
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of WB6BNQ
Sent: 05 November 2010 12:11 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Setting clocks 100 years ago
OK Bob,
I'LL bite ! Why is it 1:00 pm for the ball ?
Bill....WB6BNQ
Bob Marinelli wrote:
> Hi Murray,
>
> Actually, the ball at Greenwich drops at 1:00 pm every day. For
> everyone who can get to London, the observatory is well worth at least
> a half day visit, they have several working Harrison clocks and yes
> you can set your wristwatch at 1:00 when the ball drops :) there is
> also a wonderful transit.
>
> Cheers,
>
> Bob
>
> On Nov 4, 2010, at 4:30 PM, Murray Greenman wrote:
>
> > Navigators used chronometers to determine their longitude. If they
> > were stopped in one place long enough, they could work out longitude
> > by a complicated process of star and lunar observations; however,
> > when they left an established port, they usually took with them a
> > time standard based on local measurements of the sun and the known
> > location of the port.
> >
> > These measurements used a device called a 'Transit', which was a
> > simple telescope mounted so that it pivoted in elevation, but was
> > fixed N-S in azimuth. Midday was marked by the time at which the sun
> > transited the telescope. It thus had higher resolution than a
> > sundial. Getting N-S axis correct involved determining by iteration
> > and surveying the axis that gave maximum elevation at time of
> > transit.
> >
> > Once the transit was observed, a large ball on top of the building
> > was dropped, indicating midday, and in some locations a cannon was
> > also fired. Ships in port could observe the ball drop and hear the
> > cannon. To this day the ball drops at midday at Greenwich.
> >
> >
> > 73,
> > Murray ZL1BPU
> >
> >
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