# Extra Leap Second Added: Scientific Basis of Phenomenon

## Extra Leap Second Added: Scientific Basis of Phenomenon

Question: A leap second will be added to the end of June 30,2015. Discuss the science behind this phenomenon.

• Leap second or an extra second added to a day will be added at the end of June 30 2015

• This will make it longer than other days in a month

• The sequence of the time will read in the following way:

• 30th June 2015: 23 hrs, 59 minutes, 59 seconds

• 30th June 2015: 23 hrs, 59 minutes, 60 seconds

• 1st July 2015: 00 hrs, 00 minutes, 00 seconds

• Normally, one would have gone straight from the first point to the third

• Decision for the addition was taken by International Earth Rotation and Reference Systems Service

• This is an international body which tracks minor changes in the rotation of the earth and declares time changes accordingly

• It is based in Paris

The science behind this

• Earth’s rotation is slowing down gradually a bit

• Leap seconds are the way to account for that

• Day lasts for 86,400 seconds which is the case as per a time standard people employ in their daily lives namely the Coordinated Universal Time or UTC
• This has been calculated through precise atomic clocks

• Cesium clock is accurate to one second in 1,400,000 years

• Mean solar day(average length of day based on how long it takes earth to rotate) is around 86,400.002 seconds in length

• This has resulted because earth’s rotation is slowing down as a result of the braking force caused by gravitational tussle between earth, the moon and the sun

• Difference of 2 milliseconds or 2/2000th of a second if repeated every day for an entire year adds up to a second

• The factors causing variance in length of individual days are as follows:

• Seasonal and daily weather variations

• Dynamics of earth’s inner core

• Variations in movement of oceans and atmosphere

• Variances in groundwater and ice storage and oceanic and atmospheric tides

• Atmospheric variations caused as a result of El Nino can slow down earth’s rotation, increase length of day by as much as 1 millisecond or a 1000th of a second

• Scientists monitor the time taken for earth to complete full rotation using VLBI or Vert Long Baseline Interferometry

• Measurements are conducted through a wide network of stations which provide the analysing and archiving of data collected

Facts and Stats

• Mean solar day has not been 86,400 seconds long since the year 1820

• From 1972, there have been 25 additions of leap seconds; these were always added on June 30

• Prior to 1972, different adjustments were carried out