Chronology Lab

Time glossary

Common terms clarified so every planner and chronologist shares the same vocabulary.

Key terms

Definitions

UTC

Coordinated Universal Time is the atomic-timescale baseline. Always reference UTC for technical specs and logs.

Leap second

An extra second added to UTC to keep atomic time aligned with Earth’s rotation when it slows.

ISO week

Week number per ISO 8601, starting Monday; week 1 contains January 4 of that year.

Gnomon

A simple vertical indicator used to track solar time via its shadow.

Time zone

Regions that share the same UTC offset; some adjust for daylight saving time on local schedules.

Atomic second

Defined by 9,192,631,770 oscillations of a cesium transition—our most precise second yet.