[time-nuts] Setting clocks 100 years ago

WB6BNQ wb6bnq at cox.net
Fri Nov 5 00:11:08 UTC 2010


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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