No leap second will be introduced at the end of December 2026
The International Earth Rotation and Reference Systems Service (IERS) has declared no leap second for December 2026, a decision that always sparks fascination on HN. This technical bulletin highlights the ongoing, unpredictable dance between atomic time and Earth's erratic rotation. Hacker News users chime in with appreciation for the IERS's dramatic pronouncements, delve into the geophysical forces at play, and debate the perennial software engineering headaches these adjustments cause for critical systems.
The Lowdown
The International Earth Rotation and Reference Systems Service (IERS) has issued its Bulletin C 72, formally announcing that no leap second will be introduced at the end of December 2026. This periodic declaration is critical for authorities involved in time measurement and distribution globally.
- The bulletin clarifies that the difference between Coordinated Universal Time (UTC) and International Atomic Time (TAI) has remained at -37 seconds since January 1, 2017, "until further notice."
- Leap seconds are added (or theoretically removed, though none have been) to UTC to keep it within 0.9 seconds of UT1 (astronomical time based on Earth's rotation).
- These adjustments can occur at the end of June or December, and Bulletins are issued every six months to confirm or deny the need for an upcoming leap second.
- The need for leap seconds arises from the Earth's slightly unpredictable and variable rotation speed.
This announcement underscores the continuous effort required to synchronize human-defined atomic time with the dynamic and ever-changing rotational period of our planet.
The Gossip
Galactic Governance & Grandiosity
Many users expressed amusement and appreciation for the formal, almost sci-fi language used by the International Earth Rotation and Reference Systems Service (IERS) and its officials. Phrases like "To authorities responsible for the measurement and distribution of time" and titles such as "Director of the Directorate of Time" were singled out for their dramatic, authoritative tone, prompting humorous comparisons to Douglas Adams novels and 'Time Lords'.
Earth's Erratic Ephemeris
A core theme revolved around the physical reasons behind the unpredictability of Earth's rotation and thus, leap seconds. Commenters explained that geological activity, movement in the outer core, atmospheric and oceanic currents, melting ice, and even human activities like dam building contribute to subtle, unpredictable changes in the Earth's rotational speed and axis. The discussion highlighted that Earth's rotation has recently been unusually fast, precluding the need for a positive leap second.
Systemic Stress & Software Solutions
The discussion often turned to the challenges leap seconds pose for high-reliability computer systems. Several users debated whether leap seconds belong at a different "abstraction layer," perhaps within time zones, while others argued against this due to global impact. The concept of "time smearing"—adjusting the duration of seconds over a period—was brought up as a common solution, notably used by systems like Google Spanner, to mitigate disruptions caused by these adjustments without breaking strict ordering.