popularmechanics.co.za 17system company, and former chief scientist for time
services at the US Naval Observatory.
‘Since we can’t change the rotation of the Earth,
we change what time it is by adding leap seconds,’
says James L Davis, PhD, a geodesist (someone who
monitors the Earth’s position) and Lamont research
professor at the Lamont-Doherty Earth Observatory of
Columbia University.
The ITU has added 27 leap seconds since 1972 to
account for years when the Earth’s rotational speed slowed
overall. But 2020’s increased rate of rotation produced a
faster year – clocking 28 seconds faster than the previous
fastest year ever recorded. With the trend appearing
to continue into the near future, some scientists are
considering introducing a negative leap second.
This could have unintended consequences, however,
disrupting servers and operating systems like a mini Y2K.
Most programming languages use very rudimentary
timekeeping based on primitive clock hardware inside
the computers themselves. To keep track of ‘real time’,
computers must ping global timekeeping servers for tiny
corrections instead of entire seconds.
Regular leap seconds already create headaches, says
Matsakis, as many computer programmers are unable to
program around the extra second.
‘Instead of going to zero when it’s 11:59:59 pm, a clock,
in military time, goes to 11:60,’ says Davis. And for some
programs, that extra second wreaks havoc. A negative leap
second brings the additional challenge of convincing
a computer that it’s 12:00:00 for a second second in a row.
Consider GPS signals, which measure location and time,
and move at the speed of light. ‘An error of a nanosecond
translates to a foot of error. So if you’re off by a second
when you’re analysing GPS, you’ll be way off target,’
says Davis.
Variations in Earth’s rotational speed are affected by
internal friction arising from tidal forces from the Moon
and Sun and changes to the shape of Earth. According to
NASA, Earth’s climate, including winds and atmospheric
pressure systems, may also affect the rate of rotation. Post-
glacial rebound – which, since the end of the last ice age,
has slowly given birth to land masses due to a change in
the distribution of ice mass and sea levels across the globe- also changes the Earth’s shape.
‘This is the ice skater analogue,’ Davis says. ‘As an ice
skater is spinning, they can fling their arms out and they’ll
spin more slowly. Inversely, if the skater has their arms
out and tucks them towards their body, they’ll spin faster.’
In this instance, think of post-glacial rebound as the tucked
arms of the skating Earth.
Without 29 February, the
changing of the seasons
would drift across the
calendar year, thanks to
our lap around the Sun
clocking 365.24 days.
Because of that 0.
days – or five hours 48
minutes and 46 seconds- a leap year must be
skipped once every
three out of four centuries.
Though the years 1600
and 2000 were leap years,
1700, 1800, and 1900 were
not, and 2100 won’t be
one, either.
The first leap year
PH occurred in 45 BCE, at
OT
OG
RA
PH
Y:^
GE
TT
Y^ I
MA
GE
S.^
PH
OT
O^ I
LLU
ST
RA
TIO
N:^
CO
LIN
M
CS
HE
RR
Y
MAY / JUNE 2022 17Across shorter, daily-to-decadal time scales, wind is one
of the biggest natural factors to affect rotation, Davis says.
‘When winds move, they exchange momentum with the
solid Earth. They trade off energy and produce a lot of
friction.’ This, coupled with the Earth’s oceans and their
currents, the atmosphere, tides, and even human
movement, also has an impact on rotation.
To counter these intersecting forces, some scientists
offer the negative leap second as a solution to maintain
alignment between UTC and UT1. Ultimately, though, the
decision will be up to the International Earth Rotation and
Reference Systems Service (IERS), which maintains global
time standards.HOW
WE GOT
THE LEAP
YEAR
AN ERROR OF A NANOSECOND
TRANSLATES TO A FOOT OF
ERROR. SO IF YOU’RE OFF BY A
SECOND WHEN YOU’RE ANALYSING
GPS, YOU’LL BE WAY OFF TARGET.
the behest of Julius
Caesar and his estab-
lishment of the 12-month
Julian calendar with a
quadrennial leap day
repeating 23 February.
Caesar’s calendar was still
off by 11 minutes, which
centuries later presented
a problem for the Catholic
Church as it threw off
their Easter schedule.
To fix this, the Gregorian
calendar – our modern
calendar – named after
Pope Gregory XIII, was
created, which updated
the Julian calendar.- Daisy Hernandez