(3) Indian Standard Time is calculated on the basis of 82.30' E longitude, in Shankargarh Fort, Mirzapur,Uttar Pradesh which is nearly on the corresponding longitude reference line. The speed of Sun never stays same for a whole year. It keeps on changing every time. That is why, time on earth is different at different places. The standard time for every country is different. The local time for every country is also not same. The time of Greenwich is taken as standard time for the whole world and the standard time of all the countries is calculated according to this time. The Sun is above Greenwich Meridian line at 12 p.m in Greenwich. When Sun shifts from Greenwich Meridian towards west, the time changes by 1 degree. 1 degree is equal to 4 minutes. The time calculated like this is known as Greenwich Mean Time. · 15 degrees = 1 hour · 1 degree = 4 minutes · 1 minute = 4 second