[time-nuts] Greenwich time ball

[Bob Camp]

Hi

Been there done that. Rest of the family was more impressed by the view than by the chronometers ...

Bob


On Nov 4, 2010, at 8:19 PM, Bob Marinelli wrote:

> Hi Bill,
> 
> The astronomers were busy doing their noon transit sighting at noon.  They ball on Flamsteed House drops at 1:00.  The navigators on ships in the harbor were also likely doing a sight at noon, they set their clock at 1:00 by looking up at the observatory on the hill.  BTW, the view from Greenwich observatory over London is quite spectacular.  The above my recollection from a tour guide at the observatory.  Here is the official story (including an animation of the ball dropping):
> 
> http://www.nmm.ac.uk/places/royal-observatory/time-ball/
> 
> I guess this is the time to propose that, if possible, every Time Nut needs to visit Greenwich Observatory at least once :)
> 
> -Bob
> 
> On Nov 4, 2010, at 5:11 PM, WB6BNQ wrote:
> 
>> 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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> 
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