Give geographical reasons:

The local time at Greenwich is considered to be the international standard time.

Local time is the time in a particular region or country. It is determined on the basis of the apparent movement of the sun. It is same for a region or country located on the same latitude. However, countries located in different longitudes have different local times. Thus, for an international coordination between countries, the local time at Greenwich (Greenwich Mean Time) in England is considered to be the international standard time. The standard times of various countries are calculated with reference to GMT by calculating the longitudinal difference.

For instance, if it is noon at Greenwich, the Indian standard time would be 5:30 PM

Longitudinal coordinates of Greenwich = 0

Longitudinal coordinates of India = 82^o30’E

longitudinal difference = 82^o30’E

Time taken to cover one longitudinal degree = 4 minutes

Standard time of India = GMT + (82.5) *4 minutes = GMT + 330 minutes = GMT + 5:30 hours