Leap second scrapped from 2027: clock time and sky time to part ways

The world's timekeepers have voted to end the leap second. At its meeting in Versailles, France, on Thursday, October 15, 2026, the General Conference on Weights and Measures (CGPM), the body that governs the international system of units, passed a resolution by majority to stop adding leap seconds to Coordinated Universal Time (UTC) from May 20, 2027. Instead of correcting the clock each time it drifts about a second away from the Earth's rotation, the new rule lets the gap grow to as much as one hour before any correction is considered.

There are two ways to tell the time. One follows the sky: a day is one turn of the Earth, and noon is when the Sun is highest. The other follows atomic clocks, which count the vibrations of atoms and keep a second that never changes. The two do not agree exactly, because the Earth's spin is slightly irregular. It slowed over the last century, which is why leap seconds were added from 1972 to keep clock time within a second of sky time.

Each added second caused trouble for computers. Systems that run on precise time, such as telecom networks, power grids, stock exchanges, banks and satellite navigation, had to handle a minute with 61 seconds, and some ran into errors. In recent years the Earth has been spinning a little faster, raising the prospect of a minute with only 59 seconds, which had never been tested. Scrapping the leap second removes both problems, at the cost of letting clock time and sky time slowly part company.

This tension between the sky and the clock is an old one, and Indian astronomy addressed it in its own way. In the classical Indian system set out in astronomical texts such as the Surya Siddhanta, usually dated to around the 4th or 5th century CE, the day was counted from sunrise and divided into 60 ghatis of about 24 modern minutes each. Each ghati was divided into 60 palas of about 24 seconds. Water clocks were used to measure the ghati. Because the day began at sunrise, the timings shifted with the season and with place; the clock was tied to the sky, not the other way round.

The traditional calendar still works this way. A panchang, the Hindu almanac, calculates the tithi (lunar day) and other timings from the actual positions of the Sun and the Moon, which is why a tithi such as Ashtami or Navami can begin in the middle of a calendar day. The CGPM decision moves world civil time in the opposite direction: it accepts that official time will no longer follow the Earth's rotation to the second, because steady, uninterrupted counting matters more to modern machines than matching the Sun exactly.

Short-term: Nothing changes on clocks today. No leap second is scheduled before the rule takes effect, so the one added on December 31, 2016 is most likely the last. Operators of computer and network systems will need to make sure their software does not insert one after May 2027.

Long-term: UTC will run continuously and slowly drift away from the Earth's rotation; Tavella said the 37-second gap between UTC and pure atomic time should stay frozen for centuries.

Who is affected: Operators of telecom, power, banking, market and navigation systems, including those in India that rely on Indian Standard Time; astronomers and scientists who need sky-based time; and anyone studying how calendars and timekeeping systems are built.

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