Local mean time (LMT) is a form of
solar time that corrects the variations of
local apparent time, forming a uniform time scale at a specific
longitude
Longitude (, ) is a geographic coordinate that specifies the east– west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek let ...
. This measurement of time was used for everyday use during the 19th century before
time zones were introduced beginning in the late 19th century; it still has some uses in astronomy and navigation.
Past use
Local mean time was used from the early 19th century, when local
solar time or
sundial time was last used until
standard time was adopted on various dates in the several countries. Each town or city kept its own
meridian. This led to a situation where locations one degree of longitude apart had times four minutes apart.
This became a problem in the mid 19th century when railways needed clocks that were synchronized between stations, at the same time as people needed to match their clock (or the church clock) to the time tables. Standard time means that the same
time
Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past, through the present, into the future. It is a component quantity of various me ...
is used throughout some region—usually, it was either offset from
Greenwich Mean Time
Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, including being calculated from noon; as a c ...
or was the local mean time of the
capital
Capital may refer to:
Common uses
* Capital city, a municipality of primary status
** List of national capital cities
* Capital letter, an upper-case letter Economics and social sciences
* Capital (economics), the durable produced goods used fo ...
of the region. The difference between local mean time and local apparent time is the
equation of time.
See also
*
Day
*
Time zone
References
{{DEFAULTSORT:Local Mean Time
Time scales
Time in astronomy
de:Mittlere Ortszeit