Overview

• The International Rotation and Reference Systems Service confirmed July 9, July 22 and August 5 will each shave up to 1.51 milliseconds off a 24-hour day.
• Since 2020, successive record-short days have signaled an unexpected acceleration in Earth’s rotation, reversing a decades-long slowdown.
• Researchers remain unable to pinpoint whether core dynamics, ocean currents or atmospheric processes are driving the faster spin.
• Precise timekeeping systems for GPS, telecommunications and financial networks rely on stable day lengths, making millisecond variations operationally significant.
• Timekeepers are preparing for the possibility of a negative leap second by 2029 to realign Coordinated Universal Time with Earth’s faster rotation.