For more than half a century, an international group of timekeepers has been quietly adding extra seconds to the world’s clocks, a practice known as the insertion of “leap seconds.” The adjustments keep coordinated universal time (UTC) in step with the Earth’s irregular rotation.
The responsibility for monitoring Earth’s rotation and deciding when to add a leap second falls to the International Earth Rotation and Reference Systems Service (IERS), which works with the International Bureau of Weights and Measures and other scientific bodies. When measurements show that the difference between atomic time and solar time exceeds 0.9 seconds, the IERS announces a leap second to be inserted at the end of June or December.
Because the planet’s spin is gradually slowing and subject to short‑term variations, the length of a day is not exactly 86,400 seconds. Without periodic corrections, the discrepancy would accumulate, eventually causing clocks to drift out of sync with the position of the Sun in the sky.
Since the first leap second was added on 30 June 1972, a total of 27 leap seconds have been inserted, the most recent on 31 December 2016. These one‑second adjustments are invisible to most people but are essential for precise navigation, astronomy, and telecommunications that rely on exact timing.
In recent years, scientists and technology companies have debated whether to continue the practice, arguing that the occasional extra second can disrupt computer systems and that the need for such corrections may be mitigated by alternative time‑keeping methods. Nonetheless, the IERS remains the authoritative body that monitors Earth’s rotation and will add leap seconds whenever the established criteria are met.
<small>Source: Al Jazeera — read the original story there.</small>