Time zone based on longitude
[zd,zltr,zone] = timezone(long)
[zd,zltr,zone] = timezone(long,units)
[zd,zltr,zone] = timezone(long) returns an integer zone description, zd, an alphabetical string zone indicator, zltr, and a string, zone, with the complete zone description and alphabetical zone indicator corresponding to the input longitude long.
'degrees' — decimal degrees
Given that it is locally 1330 (1:30 p.m.) at a longitude of 75ºW, determine GMT:
[zd,zltr,zone] = timezone(-75,'degrees') zd = 5 zltr = R zone = +5 R
Greenwich Mean Time (GMT) is 1330 plus five hours, or 1830 (6:30 p.m.).
Time is determined by the position of the Sun relative to the prime meridian, the zero longitude line running through Greenwich, England. When this meridian lies directly below the Sun, it is noon GMT. For local times elsewhere, the Earth is divided into 15º longitude bands, each centered on a central meridian. When a central meridian lies directly below the Sun, Local Mean Time (LMT) in that zone is noon. The zone description is an integer that when added to LMT gives GMT. For notational convenience, each zone is also given an alphabetical indicator. The indicator at Greenwich is Z, so GMT is often called ZULU time.
Note that there are actually 25 time zones, because the zone centered on the International Date Line (180º E/W) is split into two: "+12 Y" and "-12 M."