Local mean time

From Wikipedia, the free encyclopedia
Jump to: navigation, search
The equation of time — above the axis a sundial will appear fast relative to a clock showing local mean time, and below the axis a sundial will appear slow.

Local mean time, also known as apparent solar time or sun time,[1]is a form of solar time that corrects the variations of local apparent time, forming a uniform time scale at a specific longitude. Its uniformity depends only on the accuracy of the clocks used to measure it. This measurement of time was used during the 19th century before international time standardization occurred in 1883, which slowly phased out its use.

Past use[edit]

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.[1] Standard time means that the same time is used throughout some region—usually, it was either offset from Greenwich Mean Time or was the local mean time of the capital of the region. The difference between local mean time and local apparent time is the equation of time.

See also[edit]


  1. ^ a b Finch, Vernor C., Glenn T. Trewartha, M. H. Shearer, and Frederick L. Caudle (1943). Elementary Meteorology. McGraw-Hill Book Company, Inc. p. 17. ASIN B005F644PG.