Leap Second
leap-second
A one-second adjustment applied to UTC to keep it aligned with the Earth's irregular rotation.
IERS (International Earth Rotation and Reference Systems Service)
iers
Overview
IERS (International Earth Rotation and Reference Systems Service) is an international service organization headquartered at the Paris Observatory. It monitors Earth's rotation parameters, maintains the International Celestial Reference System (ICRS) and International Terrestrial Reference System (ITRS), and decides when leap seconds should be inserted into UTC. It integrates observational data from stations worldwide.
Leap Second Decisions
IERS precisely tracks Earth's rotation rate using VLBI (Very Long Baseline Interferometry), GPS, and SLR (Satellite Laser Ranging). When the difference between UT1 and UTC approaches 0.9 seconds, IERS issues Bulletin C six months in advance to announce the upcoming leap second insertion. Even after the planned abolition of leap seconds in 2035, IERS will continue monitoring and publishing UT1 data.
Earth Orientation Parameters
Beyond rotation speed, IERS monitors polar motion (wobble of the rotation axis) and precession-nutation (long-term directional drift of the axis). These Earth Orientation Parameters (EOP) are essential for precise GPS orbit determination, satellite tracking, and deep-space navigation.
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Related Terms
UTC (Coordinated Universal Time)
utc
The primary time standard by which the world regulates clocks and time, serving as the basis for civil timekeeping globally.
BIPM (International Bureau of Weights and Measures)
bipm
BIPM (Bureau International des Poids et Mesures) is the international organization headquartered near Paris that computes and maintains International Atomic Time (TAI) and Coordinated Universal Time (UTC), coordinating measurement standards worldwide.
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