Why in the news?

A recent publication in the science journal Nature highlights how climate change-induced melting of glaciers and ice sheets is altering the Earth’s rotation, potentially disrupting our timekeeping systems.
Leap seconds were added almost every year between 1972 and 1999 to adjust for Earth’s slowing rotation. But there have only been four added in the last 23 years, and the last time a leap second was added was in 2016.

What is a Leap Second?

A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) in order to synchronize atomic time with astronomical time, particularly with the Earth’s rotation.
The purpose of adding or subtracting a leap second is to keep International Atomic Time (IAT) (which is extremely precise) in close alignment with astronomical time, which is based on the Earth’s rotation and is subject to slight variations.

There are two types of leap seconds:

Positive Leap Second:
- A positive leap second is added to UTC when the Earth’s rotation slows down slightly, causing the length of a day to exceed 86,400 seconds.
- This type of leap second is necessary to bring UTC back into alignment with the Earth’s rotational time.
- Positive leap seconds are rare and occur less frequently than negative leap seconds.
Negative Leap Second:
- A negative leap second, also known as a deletion or removal of a second, occurs when the Earth’s rotation speeds up slightly, causing the length of a day to be less than 86,400 seconds.
- Negative leap seconds are extremely rare and have only been proposed but never implemented. They are considered hypothetical and have not yet been needed to adjust UTC.
- The concept of negative leap seconds is controversial and requires international agreement and coordination among timekeeping organizations.

TAI is a high-precision time scale based on the weighted average of atomic clocks (usually involving caesium or rubidium atoms) from various laboratories around the world.
It is one of the primary time scales used for scientific and technical purposes, providing a continuous and uniform time reference that is independent of the Earth’s rotation.
TAI is maintained since 1958 by the International Bureau of Weights and Measures (BIPM) in Paris, France.
Unlike UTC, which is adjusted periodically to account for the Earth’s irregular rotation, TAI is a continuous time scale that does not include any corrections for Earth’s rotation.

Glacial Melting: Accelerating melt rates in Greenland and Antarctica are redistributing weight across the planet, causing a slight deceleration in the Earth’s rotation.
Historical Context: Timekeepers have periodically added leap seconds to clocks worldwide to account for the Earth spinning faster than usual, with 27 instances recorded since the 1970s.
Planned Adjustment: The proposed “negative leap second” adjustment, scheduled for 2026, may be postponed until 2029 or later due to the recent deceleration in the Earth’s rotation.Top of Form

What is a Leap Second?

(a) It is a periodic adjustment added to International Atomic Time (TAI) to compensate for irregularities in Earth’s rotation.

(b) It is an extra second added to Coordinated Universal Time (UTC) to synchronize atomic time with astronomical time.

(d) It is a term used to describe the synchronization of atomic clocks with the oscillations of subatomic particles.