‘Leap second’syncs Indian time with Earth’s spin


The atomic clock was programmed to add an extra second to 2017 to compensate for a slowdown in the Earth’s rotation.

A ‘leap second’ was added to the Indian clock at 5:29.59 hours on Sunday to synchronise with the Earth’s rotational clock. As the atomic clock at the National Physical Laboratory (NPL) here struck 23:59:59 last night, it was programmed to add an extra second to 2017 to compensate for a slowdown in the Earth’s rotation.

Adding a second barely has an impact on the daily life, but it does matter in the fields of satellite navigation,astronomy and communication. “The Earth and rotation around its own axis is not regular, as sometimes it speeds up and sometimes it slows down due to various factors, including earthquakes and moon’s gravitational forces. As a result, astronomical time (UT1) gradually falls out of sync with atomic time (UTC), and, as and when the difference between UTC and UT1 approaches 0.9 seconds, a leap second is added to UTC through atomic clocks worldwide,” D. K. Aswal, Director of NPL, said.

Extreme precision

Adding the leap second to the Indian clock is done by the NPL under the Council for Scientific and Industrial Research. The NPL, one of the oldest laboratories in the country, has five atomic clocks and nearly 300 such pieces exist across the globe.

Atomic clocks are so precise that the margin of error in its functioning is just of a second in 100 million years. “The leap second adjustment is not so relevant for normal everyday life. However, this shift is critical for applications requiring time accuracies in the nanosecond, which are critical in the fields of astronomy, satellite navigation, communication networks,” Mr. Aswal added.

atomic clock

About Atomic Clock:

  • An atomic clock is a clock device that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element. Atomic clocks are the most accurate time and frequency standards known, and are used as primary standards for international time distribution services, to control the wave frequency of television broadcasts, and in global navigation satellite systems such as GPS.
  • The principle of operation of an atomic clock is not based on nuclear physics, but rather on atomic physics; it uses the microwave signal that electrons in atoms emit when they change energy levels. Early atomic clocks were based on masers at room temperature.


  • Currently, the most accurate atomic clocks first cool the atoms to near absolute zero temperature by slowing them with lasers and probing them in atomic fountains in a microwave-filled cavity. An example of this is the NIST-F1 atomic clock, one of the national primary time and frequency standards of the United States.
  • The accuracy of an atomic clock depends on two factors. The first factor is temperature of the sample atoms—colder atoms move much more slowly, allowing longer probe times. The second factor is the frequency and intrinsic width of the electronic transition. Higher frequencies and narrow lines increase the precision.
  • National standards agencies in many countries maintain a network of atomic clocks which are inter-compared and kept synchronized to an accuracy of 10−9 seconds per day (approximately 1 part in 1014). These clocks collectively define a continuous and stable time scale, International Atomic Time (TAI). For civil time, another time scale is disseminated, Coordinated Universal Time (UTC). UTC is derived from TAI, but approximately synchronised, by using leap seconds, to UT1, which is based on actual rotation of the Earth with respect to the solar time.
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