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On This Day: First Leap Second Added in 1972
September 17, 2021 at 08:11 PM EDT
By WeatherBug Sr. Meteorologist, James West
Don’t be alarmed, but on June 30th, 1972, the first “leap second” occurred. This periodic jump forward keeps the clocks running on time.
What exactly is a leap second? Here are a couple facts about it from the National Institute of Standards and Technology, the U.S. government’s timekeeper.
Leap Second Defined
The international standard time, Coordinated Universal Time or UTC becomes out of synch from the actual solar time based on miniscule changes in the Earth’s rotation. To keep the UTC time matching with the apparent position of the Sun and the stars, a periodic second, or “leap second” is added to the clock.
What? The Earth’s rotation is changing
Yes, the Earth’s rotation fluctuates, with the speed of rotation generally slowing. This causes the day and year to be longer, forcing the periodic insertion of a leap second to keep the world’s clocks matching the solar clocks.
How Often Are Leap Second Added?
There is not a set schedule for adding a leap second. The Earth’s rotation fluctuates, and scientists use precise measurements to determine the next leap second. International standard organizations work to keep the time between the solar time and the more precise atomic clock time (UTC) within plus or minus 0.9 seconds.
Most leap seconds are added on the last second of the months of June or December, ensuring the least interruption in timekeeping. The last leap second was added on December 31, 2016.
Why Is This Important?
The Coordinated Universal Time (UTC) is a precise time used in communication, navigation and even weather forecasting. UTC provides a precise frame of reference.
For meteorologists, the weather balloons used to measure upper air winds and temperatures are released around the world at 0 UTC and 12 UTC. This coordinated launch provides a precise snapshot of global weather patterns used to run the high-power computer weather models meteorologists utilize to create weather forecasts. This “snapshot” would not be possible if every weather service used local times to measure atmospheric conditions.
Although time cannot be stopped, every so often it will leap ahead.
What exactly is a leap second? Here are a couple facts about it from the National Institute of Standards and Technology, the U.S. government’s timekeeper.
Leap Second Defined
The international standard time, Coordinated Universal Time or UTC becomes out of synch from the actual solar time based on miniscule changes in the Earth’s rotation. To keep the UTC time matching with the apparent position of the Sun and the stars, a periodic second, or “leap second” is added to the clock.
What? The Earth’s rotation is changing
Yes, the Earth’s rotation fluctuates, with the speed of rotation generally slowing. This causes the day and year to be longer, forcing the periodic insertion of a leap second to keep the world’s clocks matching the solar clocks.
How Often Are Leap Second Added?
There is not a set schedule for adding a leap second. The Earth’s rotation fluctuates, and scientists use precise measurements to determine the next leap second. International standard organizations work to keep the time between the solar time and the more precise atomic clock time (UTC) within plus or minus 0.9 seconds.
Most leap seconds are added on the last second of the months of June or December, ensuring the least interruption in timekeeping. The last leap second was added on December 31, 2016.
Why Is This Important?
The Coordinated Universal Time (UTC) is a precise time used in communication, navigation and even weather forecasting. UTC provides a precise frame of reference.
For meteorologists, the weather balloons used to measure upper air winds and temperatures are released around the world at 0 UTC and 12 UTC. This coordinated launch provides a precise snapshot of global weather patterns used to run the high-power computer weather models meteorologists utilize to create weather forecasts. This “snapshot” would not be possible if every weather service used local times to measure atmospheric conditions.
Although time cannot be stopped, every so often it will leap ahead.