Thanks for that, an enjoyable lecture ! Does anyone know more about the question at 1:05:50 - a difference between GMT and 'London time' used by airlines ? The questioner seemed sure it wasn't daylight savings, but I live only half a degree east of the meridian and am not aware of any other timezone.
On Sun, Jan 2, 2022 at 4:51 AM Tom Van Baak <t...@leapsecond.com> wrote: > Hal Murray wrote: > > where do you get the time? > > The new years celebrations last night remind me of another source of > time: time balls. > > Although a bit of nostalgia these days or even a joke, time balls were > clever, precise, and a critical part of naval infrastructure in the 19th > century, lasting well into the 20th century, and still operational daily > in Greenwich (not right now due to refurbishment). It falls into the > category of "time dissemination"; you know, WWV, GPS, UTC, NTP, and all. > > The sound of church bells gave approximate time, partly because their > use case didn't require high precision and partly because sound travels > only one foot per millisecond. Related: starter pistols at track events; > clapperboards on movie sets; timing thunderstorms with lightning. > > But light, as you know, travels literally a million times faster, one > foot per nanosecond. Thus the optics of a time ball solved the latency > problem of setting chronometers onboard ships in the bay. Fun fact: The > Beagle (of Charles Darwin fame) carried 25 chronometers. This is every > time nuts justification for having so many clocks at home. ;-) > > ---- > > If you want a fun timely project I'm waiting for a time nut to make a > GPS controlled desktop Arduino time ball. With clever design it could > re-arm itself and mark the precise time as often as once a minute > instead of once an hour or once a day. > > Alternatively, if you allow the ball to free-fall 16 feet it takes > exactly one second. With clever design and multiple balls you could make > a continuous 1BPS (one ball per second) clock where each ground hit > exactly triggers the next ball release. This would get you front page on > hackaday. Lots of time nut fun looking at jitter and drift, at > temperature and pressure effects. And of course the ADEV would be > priceless. Seriously, some mechanical clocks teach you more about the > art of clock measurement and data analysis than a boring atomic > frequency standard or GPSDO. > > Welcome to 2022, and may we all have a better time this year. > > /tvb > > Time ball rabbit hole: > > https://en.wikipedia.org/wiki/List_of_chronometers_on_HMS_Beagle > https://en.wikipedia.org/wiki/Ship%27s_chronometer_from_HMS_Beagle > > https://en.wikipedia.org/wiki/Time_ball > > https://www.bbc.com/news/uk-england-humber-58559814 > "Time balls: The rise and fall of a timekeeping icon" > > > https://www.nytimes.com/2004/12/30/opinion/a-brief-history-of-time-balls.html > "A Brief History of Time Balls" > > > https://nmmc.co.uk/wp-content/uploads/2016/04/120330_The_Falmouth_Timeball.pdf > "The Falmouth Time Ball", by Ronald S Hawkins [ superb historical & > technical details ] > > > https://hs-ny.org/schedule/2019/5/6/the-ups-and-downs-of-the-greenwich-time-ball-an-overview-of-its-history-mechanics-and-upkeep > https://youtu.be/ubvmCWet6iU > > https://journals.sagepub.com/doi/abs/10.1177/002182868101200301 > "The First Time Balls" > Journal for the History of Astronomy > > https://adsabs.harvard.edu/full/1970JBAA...80..208H > "The Story of Greenwich Time" > > > https://www.bbc.com/travel/article/20191212-the-invention-that-inspired-a-new-york-tradition > "The invention that inspired a New York tradition" > > > https://www.xyht.com/gnsslocation-tech/the-clocks-at-the-center-of-the-universe/ > "The Clock(s) at the Center of the Universe" > > ---- > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send > an email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.