There is a general understanding among the countries of the world to select the standard meridian in multiples of 7°30' of longitude. That is why 82°30'E has been selected as the Standard Meridian of India.
This meridian passes through the Mirzapur district (near Allahabad now Prayagraj) in the state of UP. Indian Standard Time is 5 hours and 30 minutes ahead of Greenwich Mean Time (GMT).
Indian standard Meridian passes through total 5 states which are Uttar Pradesh, Madhya Pradesh, Chhattisgarh, Odisha and Andhra Pradesh.
There are total 360 longitudes. All these longitudes divide the earth into two equal parts and therefore they are also known as Great Circle. Since the earth rotates 360° in about 24 hours, which means 15° in an hour or 1° in four minutes.
Therefore the difference in every 15° longitude is 1 hour. The earth rotates from west to east, so every 15° we go eastern wards the local time is advanced by an hour and vice versa.
The whole world has been divided into 24 Standard time zones, each of which differs from the next by 15° in longitude or one hour in time.
Latitudes and Longitudes
