Local Time, Standard Time and Greenwich Mean Time (GMT)
Local Time: Parallels of longitude determine the time at a place. Local time varies, from GMT (London) at the rate of four minutes/degree of longitude.
Standard Time: It is the uniform time fixed by each country. As the local time is found to vary constantly from one
Greenwich Mean Time (GMT): It is the UK Standard time; it is based on the local lime of the meridian passing through Greenwich near London.
International Date Line: The 180o east meridian and 180o west