The world is divided into regions that share the same standard time so that clocks align with local solar day. Each region is a time zone. Crossing zones is what creates jet lag on long journeys.

Zones are nominally fifteen degrees of longitude wide, yet political boundaries produce many irregularities. Some places observe half-hour or quarter-hour offsets. Daylight saving shifts further complicate schedules for part of the year. Flight times and international meeting planning must constantly account for these differences.

Travelers adjust watches and devices on arrival; body clocks adjust more slowly. Clear itineraries list local times to avoid missed connections or appointments. Awareness of time zones is a basic literacy of long-distance travel.

• Geographic region sharing a common standard time
• Creates time differences between distant places
• Affects flight schedules and body clocks
• Modified in places by daylight saving rules