The Longest Day
If some of our readers felt that the first day of this
month felt unusually long and dreary, they would have been quite right,
because the 1st of July was the longest day of the year. In fact, it
was precisely 1 second longer than any other day of the year 2012. This
is because the people who have better clocks than the rest of us,
decided to insert a leap second at midnight on the 30th of June 2012.
But because of British Summertime, this actually happened at 1 o'clock
on the 1st of July. Experienced readers will instantly know by now,
that the rest of this article is going to be wonderfully complicated!
The time standard clocks adhere to is UTC - Coordinated
Universal Time - and all computers, electronic
items and alarm clocks - if they are on time - adhere to this
standard. In the UK this is broadcast by the National
Physical Laboratory via the Anthorn (formerly Rugby) transmitter. This
broadcasts the time measured by the atomic clock in the NPL laboratory.
Unfortunately our planet is not so precise. The revolution of the earth
around its axis is slowing down. This is caused by tidal friction,
earthquakes and other natural variations. Hence a correction has to be
made every once in a while. The News Browser - sparing no
expense - commissioned the writing of a special computer program to
show the insertion of the leap second in greater detail. Two screen
shots from this are shown below.
The yellow graph represents the signal from the atomic
clock as it is broadcast. The line of 0's and 1's is the decoded
signal. Below this are partitions showing what each of the binary
groups represents : offset, year, month, day and so on. We
have pointed to the interesting bits with red text.
The top picture shows the signal from the atomic clock
before the change was made. Notice the six markers indicating that UTC
was 600 milliseconds behind Greenwich Mean Time.
The bottom picture was taken after the leap second was inserted. Notice
that the markers have changed to +400 ms. From
-600ms to +400ms is exactly 1 second.
Isn't all this wonderfully complicated and interesting? You
can watch a recording of the above procedure via the link below:
video of the 2012 leap