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The Relativity Of A Second - It's Taking A Leap

A leap second is being added to the clock on June 30, 2015.

A leap second is being added to the clock on Tuesday to synchronize the Universal Time (UT), based on the earth’s rotation, and the International Atomic Time (TAI), which is measured using the weighted average of approximately 200 atomic clocks from around the world.

Charles Swenson is a professor and director of the Center for Space Engineering at Utah State University. He said atomic clocks have changed the way we measure time.

“We started creating these things we call atomic clocks," Swenson said. "And they are so precise that we can actually measure as the earth speeds up or slows down due to things like - an earthquake will shift the rotation rate of the earth and giant cyclones or hurricanes or rotation of the atmosphere will slowly shift the spin rate of the earth.”

Swenson said scientists and the U.S. Naval Observatory in Washington D.C. are the people mainly responsible for measuring time and the earth’s rotation.

“They use quasars," Swenson said. "They use objects that are so, so far away that it doesn’t matter as the earth goes around the sun in it's orbit, it looks  like it’s exactly the same place. And they measure when this quasars, these objects, come overhead with radio telescopes and they measure them very precisely.”

Because of the precision of atomic time and the unpredictable nature of earth, the leap second was introduced in 1972 to calibrate the difference between the two.

Swenson said the point of adding or subtracting the leap second is to keep the sun directly overhead the prime meridian found in Greenwich, London.