Standard time zones could be defined by geometrically subdividing the Earth's spheroid into 24 lunes (wedge-shaped sections), bordered by meridians each 15° of longitude apart. The local time in neighboring zones would differ by one hour, and the variation in the position of the sun from one end of the zone to the other (east vs. west) would be at most 1/24 of the sky. Most of the 25 nautical time zones (specifically UTC−11 to UTC+11) are indeed defined this way, and are 15° of longitude wide. An hourly zone in the central Pacific Ocean is split into two 7.5°-wide zones (UTC±12) by the 180th meridian, part of which coincides with the International Date Line.
On land, it is more convenient for areas in close commercial or other communication to keep the same time, so time zones tend to follow the boundaries of countries and their subdivisions instead. Of the 40 time zones on land, most are offset from Coordinated Universal Time (UTC) by a whole number of hours (UTC−12 to UTC+14), but a few are offset by 30 or 45 minutes from a nearby hourly zone. Daylight saving time is used in some higher-latitude countries to manipulate clock time with respect to the position of the sun for parts of the year, typically by changing clocks by an hour. Many land time zones are skewed toward the west relative to the corresponding nautical time zones, which also creates a permanent daylight saving time-like offset. Computer operating systems use either UTC or a local time zone to time-stamp events.
