Time zone based on longitude
[zd,zltr,zone] = timezone(long)
[zd,zltr,zone] = timezone(long,
[zd,zltr,zone] = timezone(long) returns
an integer zone description,
zd, an alphabetical
string zone indicator,
zltr, and a string,
with the complete zone description and alphabetical zone indicator
corresponding to the input longitude
[zd,zltr,zone] = timezone(long, specifies
the angular units with a standard angle
The default value is
'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."
National and local governments set their own time zone boundaries
for political or geographic convenience. The
does not account for statutory deviations from the meridian-based