Earth spins faster: One of the shortest days on record

Explainer

TNS

Chandigarh, Updated At : 08:28 PM Aug 06, 2025 IST

1. What happened on August 5, 2025?

• Earth completed a solar day approximately 1.25 ms shorter than the standard 24 hours (Rs 86,400 seconds), making it one of the shortest days on record.

• This follows a pattern in 2025, with similarly short days on July 9 (≈1.23 ms) and July 22 (≈1.34 ms).

• The all‑time shortest day since atomic timekeeping began was July 5, 2024 when the solar day was 1.66 ms shorter than normal.

2. Science behind these anomalies

Earth’s variable rotation

• The mean solar day isn’t fixed; it fluctuates due to variations in Earth’s moment of inertia — influenced by tides, atmospheric circulation, core motions and mass redistribution (e.g. melting ice).

• While the long-term trend since antiquity is toward slower rotation and lengthening days (Rs +1.4 ms per century) due to tidal friction from the Moon, recent years (since Rs 2020) have seen temporary acceleration.

Role of the Moon

• Shorter solar days often correspond to days when the Moon’s declination (latitude relative to Earth’s equator) is at a maximum, which subtly alters tidal forces and rotational speed .

Internal dynamics & climate factors

• Neither atmospheric nor ocean models fully explain the consistent acceleration, suggesting changes in Earth’s liquid core or internal dynamics may be responsible.

• Paradoxically, melting polar ice (moving mass toward the equator) acts to slow rotation and may have partly offset faster spinning — suggesting complex climate‑rotation interplay.

3. Timekeeping & leap‑second implications

• UTC (Coordinated Universal Time) is maintained via atomic clocks (Rs 450 worldwide), requiring occasional leap second adjustments to stay in sync with Earth’s rotation.

• Thus far, 27 positive leap seconds have been added since 1972; none since 2016.

• With Earth now accelerating, experts foresee a possible negative leap second (subtracting a second) as early as 2029 — a first in timekeeping history.

• International bodies plan to phase out leap seconds by 2035, but removing a second would test the system like never before.

4. UPSC‑relevant themes & analytical angles

Science & technology (alignment with UPSC syllabus)

• Geophysical processes affecting Earth’s rotation — tidal friction, mass redistribution and core dynamics — tie into static Earth science.

• Precision timekeeping infrastructure, atomic time synchronisation and leap second governance link to science and technology aspects of governance.

Governance & policy dimensions

• The move toward negative leap seconds raises regulatory and technological challenges for global governance of time standards.

• The eventual elimination of leap seconds by 2035 signals evolving governance of global timekeeping protocols.

Environmental & climate interaction

• The surprising impact of glacial melt and mass redistribution on Earth’s rotation illustrates the broader nexus of climate change, hydrosphere dynamics and planetary behaviour.

5. UPSC‑style questions

Short‑answer (50–100 words)

1. Explain the significance of Earth completing a rotation 1.25 ms faster than usual on August 5, 2025.

2. How do changes in Earth’s liquid core and melting polar ice influence the length of a solar day?

Long‑answer (250–300 words)

1. Discuss how lunar declination and Earth’s internal dynamics contribute to anomalies in day length, with reference to recent observations in 2024-2025.

2. Evaluate the implications of negative leap seconds for global timekeeping and governance frameworks.

Essay/analytical (500+ words)

1. Analyse the interplay between geophysical processes (tidal forces, core‑mantle coupling, climate‑induced mass redistribution) in causing fluctuations of Earth’s rotational period. How does this challenge traditional models of Earth’s rotation?

2. With Earth spinning faster and the possibility of a negative leap second emerging, critically assess the technological, policy and governance challenges of synchronising Coordinated Universal Time with a changing planet.

Earth spins faster: One of the shortest days on record

Ravneet Kaur

TNS

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