Good question, probably to allow the Astronomer Royal's staff to take a transit and check their clocks for that day. Alan
----- Original Message ----- From: "WB6BNQ" <[email protected]> To: "Discussion of precise time and frequency measurement" <[email protected]> Sent: Friday, November 05, 2010 12:11 AM 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 > > > > > > > > > _______________________________________________ > > > time-nuts mailing list -- [email protected] > > > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > and follow the instructions there. > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
