pituuspiirivyöhyke

A pituuspiirivyöhyke, or time zone, is a region that observes a uniform standard time for legal, commercial, and social purposes. It is determined by the Earth's rotation and the need for a standardized way to measure time across different geographical longitudes. The Earth rotates 360 degrees in approximately 24 hours, meaning that for every 15 degrees of longitude, there is roughly a one-hour difference in solar time.

Historically, local solar time was used, leading to inconsistencies within even small regions. The development of railways and telegraphy in the 19th century highlighted the need for a more standardized system. This led to the establishment of the International Meridian Conference in 1884, which adopted the Greenwich Meridian (0 degrees longitude) as the Prime Meridian and established a system of 24 standard time zones, each approximately 15 degrees wide.

These zones are typically designated by their offset from Coordinated Universal Time (UTC), which is based on atomic time and is the successor to Greenwich Mean Time (GMT). For example, Central European Time (CET) is UTC+1, and Eastern Standard Time (EST) in North America is UTC-5. While the ideal time zone boundaries follow lines of longitude, political and geographical considerations often result in irregular zone shapes. Many countries also observe daylight saving time, where clocks are advanced by an hour during warmer months to make better use of daylight. This further complicates the exact boundaries and observances of time zones.