Dictionary term
Leap Second
Direct answer
Leap Second: A Leap Second is a one-second adjustment that may be inserted into or removed from UTC to keep it close to UT1.
A Leap Second adjusts UTC by one second relative to Earth rotation.
A Leap Second adjusts UTC by one second relative to Earth rotation.
A cycle or timeline schematic for comparing the named timekeeping concept.Quick reference
- Use when
- Use Leap Second in precise timestamp parsing, time-service design, and explanations of UTC versus continuous atomic scales.
- Do not use it for
- Do not predict a leap second from a calendar pattern; announcements depend on measured Earth rotation and current international policy.
- Reference category
- Calendars & Timekeeping
- Related terms
- UTC Offset, Delta T, Calendar, Julian Date
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The story behind Leap Second
Leap seconds became part of UTC in 1972 under international timekeeping arrangements.
Leap Second in spiritual tradition
Spiritually, the leap second shows global systems adapting carefully to a planet that does not rotate like a perfect clock.
Leap Second: fact and faith, kept distinct
This is a factual calendar, astronomy, Earth-science, cultural-history, or observational reference. It can support wonder and practical planning without becoming a claim of fate, spiritual causation, or private revelation.
Leap Second in numerology
Leap Second is not a numerology claim. Any numbers attached to it should retain their ordinary scientific, calendrical, navigational, or historical meaning unless a separate symbolic interpretation is clearly labeled.
Why Leap Second matters
Atomic seconds are uniform while Earth rotation varies, so UTC policy has used occasional adjustments to limit their separation.
Leap Second at work: an example
A positive leap second can label an extra instant 23:59:60 UTC at an authorized month end.
Where interpretation stops
Leap Second is presented as sourced astronomy, calendrical, Earth-science, cultural, or instrument-history reference. Definitions should distinguish measured phenomena from civil convention and historical interpretation, preserve location and time dependencies, and avoid turning factual sky data into a deterministic personal claim.
Sources and editorial method
Research references used for this entry include:
- BIPM SI Brochure Annex: Time - International metrology reference for the SI second, TAI, UTC, and Terrestrial Time.
- IERS Conventions (2010), Technical Note 36 - International standards for Earth rotation angle, reference systems, time arguments, and Earth-orientation data.
- NIST: UTC(NIST) Time Scale - Official description of UTC realization, atomic time, and leap-second coordination.
- Source
- The Great Almanac Dictionary
- Category
- Calendars & Timekeeping
- Also appears in
- Calendars & Timekeeping
- Aliases
- None listed
- Last updated
- 2026-07-16
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Speak with the OracleRelated terms
More in Calendars & Timekeeping
- Modified Julian Date
- Sidereal Day
- Tropical Month
- Anomalistic Month
- Calendar Month
- Dominical Letter
- Equation of Time
- Intercalary Day
Common questions
What is Leap Second?
A Leap Second is a one-second adjustment that may be inserted into or removed from UTC to keep it close to UT1.
How is Leap Second used in an almanac?
Use Leap Second in precise timestamp parsing, time-service design, and explanations of UTC versus continuous atomic scales.
What should I avoid when interpreting Leap Second?
Do not predict a leap second from a calendar pattern; announcements depend on measured Earth rotation and current international policy.
