The first public time signal was broadcast from  the roof of Flamsteed House in 1833. The idea of dropping a ball at a predetermined time was the brainchild of Captain Wauchope, RN, and was tested at the Naval College at Portsmouth before Maudslay & Field were commissioned to install the first Greenwich time-ball in that year.

The signal was (and is) given at 1 p.m. because the astronomers would be busy checking the rates of their clocks against the sun’s transit at noon. At 12.55 p.m. the ball is hoisted half-way up the mast – originally a signal for navigators on ships in the Thames and London docks to be ready.  At two minutes to the hour the ball is hoisted to the top of the mast and then drops precisely at 1 p,m. From this, sea captains about to sail could check the rate of their marine chronometers, which were in wide use by the 1830s.*

*From the Royal Observatory Greenwich Souvenir Guide

Albert Einstein

This year’s leap second—the 26th to be added to UTC since 1972—exists because time was traditionally based on a full rotation of the Earth and was related to heavenly bodies, which defined the length of the day.

This rotational time, called UT1, divides the day into 86,400 seconds.

But the atomic era demanded more exact timekeeping, and the world began doing business by UTC in 1972.

The two time scales, though, aren’t quite in sync, because Earth spins a bit slower each year due to tides and internal processes that create a gap between the two scales.

The International Earth Rotation and Reference Systems Service monitors this difference and periodically inserts a leap second to keep the two in tandem.

The difference between atomic and rotational time is tiny—only an hour or so every thousand years.

But the leap second causes a host of timekeeping issues, because no clock can accommodate an extra second.

It probably seems a little trivial to bother about seconds and put so much effort into correcting the slight anomaly, but…

“for the stock exchange, one second is important. For an airport, one second is important. For global navigation satellite systems, the difference of a second is unacceptable.”

Navigation systems work by measuring the time it takes a signal to travel between a known satellite location and a receiver. Such systems require extreme precision on the level of nanoseconds, or billionths of a second.

Information from National Geographic.

Over at Vision and Verb I invite you to sit and rest a while with me.

I had an hour to spare, so what did I do? I read the book I was carrying in my bag, it is called ‘Mapping Time‘. The truth is always stranger than fiction

Weight loss… The graph speaks for itself.