What Is a Time Zone?

A time zone is a region that observes a uniform standard time for legal, commercial, and social purposes. Key concepts:

• Basis: Earth’s rotation; 24 longitudinal zones, each ~15° wide, centered on meridians.
• Reference: Coordinated Universal Time (UTC) at the Prime Meridian (Greenwich). Zones range from UTC−12 to UTC+14.
• Offsets: Most are whole-hour offsets; some use half- or quarter-hour (e.g., UTC+5:30 India, UTC+12:45 Chatham Islands).
• Daylight Saving Time (DST): Many regions shift clocks +1 hour in summer, temporarily changing offset (e.g., EDT = UTC−4 vs. EST = UTC−5).
• Standardization: Managed by IANA Time Zone Database; used globally in computing, aviation, scheduling.
• Abbreviations: EST, PST, GMT, CET, etc., though these can be ambiguous (e.g., CST = Central Standard Time in US/Canada, China Standard Time, Cuba Standard Time).

Time zones enable global coordination of travel, finance, communications, and diplomacy.