The last minute of Tuesday, June 30, will contain 61 seconds instead of 60 seconds in order to correct the atomic timeline. Atomic clocks around the world will sync with the leap second, which is required for the Coordinated Universal Time (UTC), the system that guides international civil times, synced with the Earth’s rotation.
However, atomic time and “real time” are not the same, as people use “real time” to determine the timeline of the day and month in the year. This is based on the cycle of the Sun (morning and night). But, scientists observed how long it takes for the Earth to complete a full rotation, using a more accurate technique known as Very Long Baseline Interferometry (VLBI). This time is called as Universal Time 1 (UT1), but it is not precise as cesium clock, and are usually a second apart.
“It’s taken about three years to accumulate about half a second difference,” said Michael Wouters, head of the Time and Frequency team of Australia’s National Measurement Institute.
The slight difference is because of the unpredictable Earth’s rotation. Earth interaction with the gravity of the Sun and Moon is slowing down the rotation, and Wouters added that leap seconds could occur more frequently in the future. Massive earthquakes, changes in weather and temperature could also cause the atmosphere to drag rotation of the Earth, indicating the impact of global warming.
The International Astronomical Union and the International Union of Geodesy and Geophysics (IERS), which provides data about Earth’s rotation to the global scientific community, decided to add the leap second. The agency advised that the leap second should be added in June. Wouters said that June 30 is just a convention, and it can happen any time of the month in June or December. According to NASA, leap seconds were introduced in 1972, and has been implemented since needed.