1. The Leap Second
Charlotte Bate

2. THE EARTH’S ROTATION IS SLOWING!

3. Decrease in Earth’s rotation rate Increase in LOD 1.70 ± 0.05 ms/cy

4. Causes of Rotation Rate Changes
Secular negative acceleration
Periodic variation
Random fluctuations

5. A little physics: 𝐸 𝑡𝑜𝑡 = 𝐸 𝐾 + 𝐸 𝑃 𝐿 𝑡𝑜𝑡 = 𝐿 𝑠𝑝𝑖𝑛 + 𝐿 𝑜𝑟𝑏𝑖𝑡 → 𝐿 =𝐼𝜔 𝑘
Rotation Rate Changes
A little physics:
Isolated System
Secular Deceleration
Periodic Variation
Random Fluctuations
𝐸 𝑡𝑜𝑡 = 𝐸 𝐾 + 𝐸 𝑃
𝐿 𝑡𝑜𝑡 = 𝐿 𝑠𝑝𝑖𝑛 + 𝐿 𝑜𝑟𝑏𝑖𝑡
→ 𝐿 =𝐼𝜔 𝑘
→𝐼= 𝑉 𝜌 𝑟 𝑟 2 𝑑𝑉

6. Earth and Moon system: Tidal acceleration: LOD + (2.3 ± 0.1)ms/cy
Rotation Rate Changes
Earth and Moon system: Tidal acceleration: LOD + (2.3 ± 0.1)ms/cy
Isolated System
Secular Deceleration
Periodic Variation
Random Fluctuations

7. ???  Post-glacial rebound
Rotation Rate Changes
But wait… 1.7 ms/cy = 2.3 ms/cy + x x = -0.6 ms/cy
Secular Deceleration
Periodic Variation
Random Fluctuations
Total
Earth-Moon
???
???  Post-glacial rebound

8. Rotation Rate Changes Secular Deceleration Periodic Variation
Random Fluctuations

9. 𝐿 =𝐼𝜔 𝑘 2004 Sumatra-Andaman Earthquake Rotation Rate Changes
Secular Deceleration
Periodic Variation
Random Fluctuations
𝐿 =𝐼𝜔 𝑘

10. Timescales TAI – International Atomic Time
UTC – Coordinated Universal Time
UT1 – measure of Earth’s rotation angle

11. UT1 and TAI diverge Introduction of Leap Second

12. LEAP SECOND IN DA NEWS!!!

13. Thank you!