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The Future of Leap Seconds

In Boston, the previous leap second occurred on Saturday, December 31, 2016 at 6:59:60 pm.
UTC time was December 31, 2016 at 23:59:60.

Leap seconds are added to our clocks to compensate for the Earth's slowing rotation. However, some scientists propose abolishing leap seconds in the future, redefining the way we measure time.

Earth in space. Elements of this image furnished by NASA.

Earth's rotation is a part of defining time.

Coordinated Universal Time is a combination of Universal Time - Earth's rotation - and Atomic Time.


Should Earth's Rotation Define Time?

Triggered by a questionnaire about Coordinated Universal Time (UTC) distributed by the IERS in 1999, scientists around the world began discussing the use of leap seconds. The argument revolves around the question:

Should we adjust our clocks to the Earth's slowing rotation, or should atomic clocks be solely responsible for measuring time?

A never-ending argument?

The scientific community has so far failed to reach an agreement on this topic.

  • In 2003, a meeting named “ITU-R SRG 7A Colloquium on the UTC timescale” took place in Torino, Italy, where it was suggested that time be decoupled from the Earth’s rotation and leap seconds be abolished. No decision was reached.
  • In 2005, US scientists proposed to eliminate leap seconds and replace them with leap hours. The proposal was criticized for its lack of consistent public information and adequate justification.
  • In 2012, delegates of the World Radiocommunication Assembly in Geneva, Switzerland, decided once more to postpone the decision to abolish leap seconds and scheduled a new vote for 2015.
  • In 2015, the decision was again deferred to 2023.

Leap Seconds: Pros and Cons

The computer scientist and leap second expert Markus Kuhn from the University of Cambridge lists the following arguments against leap seconds:

  • Leap seconds could cause disruptions where computers are tightly synchronized with UTC.
  • Leap seconds are a rare anomaly, which is a concern for safety-critical real-time systems (e.g., air-traffic control concepts entirely based on satellite navigation).
  • Universal Time (UT1), which is defined by Earth's rotation, is not significant in most people’s daily lives.

His arguments in favor of leap seconds include:

  • There have been no credible reports about serious problems caused by leap seconds.
  • Some computerized systems that work with leap seconds are costly to modify (eg. antennas that track satellites).
  • Computer errors caused by leap seconds can be avoided simply by using International Atomic Time (TAI) instead of Universal Coordinated Time (UTC).
  • Desktop computers and network servers have no trouble coping with leap seconds.
  • Humankind has defined time by the Earth's rotation for over 5000 years – this tradition should not be given up because of unfounded worries of some air-traffic control engineers.
  • Abandoning leap seconds would make sundials obsolete.

Despite calls by some people to retain leap seconds, atomic time advocates also argued that leap seconds were a burden because they were unpredictable.

Topics: Timekeeping, Earth

International Atomic Time (TAI)


Wednesday, October 23, 2019

TAI – Currently 37 seconds ahead of UTC

Leap Seconds Added

The difference TAI vs. UTC refers to after the leap seconds have been added

UTC DateUTC TimeDifference TAI vs. UTC
6/30/197223:59:6011 secs
12/31/197223:59:6012 secs
12/31/197323:59:6013 secs
12/31/197423:59:6014 secs
12/31/197523:59:6015 secs
12/31/197623:59:6016 secs
12/31/197723:59:6017 secs
12/31/197823:59:6018 secs
12/31/197923:59:6019 secs
6/30/198123:59:6020 secs
6/30/198223:59:6021 secs
6/30/198323:59:6022 secs
6/30/198523:59:6023 secs
12/31/198723:59:6024 secs
12/31/198923:59:6025 secs
12/31/199023:59:6026 secs
6/30/199223:59:6027 secs
6/30/199323:59:6028 secs
6/30/199423:59:6029 secs
12/31/199523:59:6030 secs
6/30/199723:59:6031 secs
12/31/199823:59:6032 secs
12/31/200523:59:6033 secs
12/31/200823:59:6034 secs
6/30/201223:59:6035 secs
6/30/201523:59:6036 secs
12/31/201623:59:6037 secs
Further leap seconds not yet announced.

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