What are time zones?
Time zones are geographic and administrative regions that share a standard civil time.
Definition and processes
Core concept Earth rotates in roughly 24 hours, so solar position and local solar time vary with longitude. The idealized 15 degrees per hour explains the concept; real legal zone borders are not straight meridians. How it is studied Governments define civil time relative to UTC. Borders, transport and seasonal daylight-saving rules can alter the relationship and may change over time.
Applications and caveats
Why it matters Flights, meetings, records and trade require time conversion. For future events use a named local time zone, not just a fixed UTC offset. Common misunderstandings Places at the same longitude need not use the same legal time. Sunrise and day length also depend on latitude and season.