On account of the vast longitudinal extent of India there is a time lag of two hours in local time between its western and eastern limits. Hence, for the sake of convenience a standard time is adopted for the entire country. The central meridian of the country, 82°30’E longitude, has been selected as the Standard Meridian of India. It passes through Mirzapur in Uttar Pradesh. The local time along this meridian is taken as the standard time of India, which is 82°30’× 4 min = 330 minutes or 5 hrs.30 min ahead of G.M.T. Because India is located to the east of Greenwich Meridian, the time is ahead of G.M.T. or Universal Time. India has a longitudinal extent of more than 29°, with the 68°7’E longitude bounding its western limit in Kachchh in Gujarat and 97°25’E bounding its eastern limit in Arunachal Pradesh (97°25’– 68°7’= 29°18’).
For each 1° longitude there is a time difference of 4 minutes. For 29° longitudes there will be a time difference of 4 × 29° = 116 minutes or 1 hrs. 56 minutes, approximately 2 hours. Hence, there is a time difference of almost two hours in the local time of Arunachal Pradesh and Gujarat with the sun rising almost two hours earlier in Arunachal Pradesh compared to Gujarat.
