Timekeeping
Coordinated Universal Time (UTC)
UTC is the primary time standard by which the world regulates clocks and time. It is derived from International Atomic Time (TAI) with leap seconds added to stay aligned with Earth's rotation.
Daylight Saving Time
Daylight Saving Time (DST) is the practice of advancing civil clocks, usually by one hour, during warmer months to shift daylight from morning to evening. Adoption, dates, and offsets vary widely by country and have changed repeatedly through history.
Why Timezone Rules Are So Complex (tzdata)
The IANA time zone database (tzdata, Olson database) is the authoritative public-domain record of world civil time rules, maintained by Paul Eggert since 2005. Its text format of Zone, Rule, and Link lines compiles via zic into the binary zoneinfo files used by every major OS and language. The data's complexity reflects real-world chaos back to 1970: Indiana county splits, Lord Howe's 30-minute DST, Samoa skipping 30 December 2011, repeatedly reversed Russian DST policy, and the 2011 Astrolabe lawsuit that briefly took the project offline.
Paul Eggert
Paul Eggert is an American computer scientist at UCLA who has edited the IANA tz time zone database since 2005 and contributed to GNU projects including grep, diff, and Bash.