See also daylight saving time.
See C. Blaise, Time Lord: Sir Sandford Fleming and the Creation of Standard Time (2001).
Official local time of a region or country. Local mean solar time depends on longitude; it advances by four minutes per degree eastward. The Earth can thus be divided into 24 standard time zones, each approximately 15° in longitude. The actual boundaries of each time zone are determined by local authorities and in many places deviate considerably from 15°. The times in different zones usually differ by an integral number of hours; minutes and seconds are the same. Seealso Greenwich Mean Time.
Learn more about standard time with a free trial on Britannica.com.
A similar service is operated in the United Kingdom by the National Physical Laboratory, broadcasting from Anthorn VLF transmitter in north-west England, and by the BBC using the 198kHz carrier of the Radio 4 national radio station with a frequency accuracy of 1 part in 10^11.