Understanding Leap Second | Ias Banenge

Context:

A recent study highlighted that due to factors like climate change and geological shifts, Earth’s changing rotation may prompt clocks to skip a second, potentially necessitating a “negative leap second” around 2029.

Relevance:

Facts for Prelims

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Understanding Leap Second

Purpose of Leap Second:

• Introduced to address the Earth’s long-term slowdown in rotation due to constant melting and refreezing of ice caps.
• Added occasionally to Coordinated Universal Time (UTC) to align global clocks with Earth’s decreasing rotation speed.

History and Implementation:

• The system of leap seconds was established in the early 1970s, with 27 positive leap seconds added to date.
• UTC is based on a time scale from over 300 precise Atomic clocks worldwide, which remain accurate within one second over millions of years.

Comparison with Astronomical Time:

• Universal Time (UT1) represents Earth’s rotation on its axis and determines a day’s length.
• Earth’s rotation is inconsistent due to factors like moon’s gravitational forces and resulting ocean tides, causing UT1 to drift from UTC.
• A leap second is added to UTC when the discrepancy between UTC and UT1 approaches 0.9 seconds, ensuring synchronization.

Timing of Leap Second Addition:

• Leap seconds are typically inserted on either June 30 or December 31.

Exploring Negative Leap Second

Definition:

• A negative leap second subtracts a second from clocks to maintain synchronization with Earth’s rotation.

Historical Context:

• No negative leap seconds have been introduced to date, primarily because the Earth’s rotation has generally been slowing down over recent decades.

Monitoring and Decision-making:

• The International Earth Rotation and Reference Systems Service (IERS) oversees Earth’s rotation monitoring and determines leap second adjustments.

Consideration of Negative Leap Second:

• Due to Earth’s recent faster spin, timekeepers have considered introducing negative leap seconds, which would subtract seconds from clocks to align with Earth’s rotation.

-Source: Indian Express

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