note 2: in 1851, the British set their prime meridian (0° longitude) through the Royal Observatory at Greenwich, England; this meridian became the international standard in 1884 and thus the basis for the standard time zones of the world; today, GMT is officially known as Coordinated Universal Time (UTC) and is also referred to as "Zulu time"; UTC is the basis for all civil time, with the world divided into time zones expressed as positive or negative differences from UTC
note 3: each time zone is based on 15° starting from the prime meridian; in theory, there are 24 time zones based on the solar day, but there are now upward of 40 because of fractional hour offsets that adjust for various political and physical geographic realities; see the Standard Time Zones of the World map included with the Reference Maps
Definition: This entry gives the name of the seat of government, its geographic coordinates, the time difference relative to Coordinated Universal Time (UTC) and the time observed in Washington, DC, and, if applicable, information on daylight saving time (DST). Where appropriate, a special note has been added to highlight those countries that have multiple time zones.
Source: CIA World Factbook - This page was last updated on December 7, 2019