21st of September 2015
Social Studies


Priyansh Shrivastava - ICSE - Class IX

Wednesday, September 16, 2015 at 19:12:PM


Dear Priyanshu,

As such there are no formulas for calculating time in various countries. There are few important facts which need to be kept in mid while calculating time. These facts are:

  • As earth completes one rotation from west to east in 24 hours, every meridian gets the direct sunlight of the sun once in every day.
  • The Earth has been divided into twenty-four time zones of one hour each. Each zone thus covers 15° of longitude. 1° of longitude is covered in 4 minutes.
  • When the Greenwich meridian gets the direct sunlight, the places located along this meridian have mid day. As the earth rotates from west to east, the places which are located to the east of meridian are ahead of Greenwich Time.
  • In the same way the places located to the west of Greenwich are behind the Greenwich Time. So to find out the local time of a place, for each 1° of longitude towards the East, 4 minutes are added and for each 1° of longitude towards the west, 4 minutes are subtracted.

Calculating Time

  • We can calculate the time of two different places with the help of their longitudes. Lucknow is located at 820 E and London is located at 0 degree GMT. If it is 12 pm in Lucknow, we can calculate the local time in London.
  • As the Earth rotates from west to east, those places that lie east of Greenwich are ahead than the places that lie to the west of Greenwich. The earth rotates  in four minute. Thus if Lucknow is located in the east of Greenwich at 820E, we will multiply 82 by 4 which will be 328 minutes or 5 hrs and 28 minutes. Therefore, time at Lucknow is 5 hrs and 28 min. ahead of London (since Lucknow is located to the east of Greenwich). So if the time in London is 12: 00 pm, we will add 5 hrs and 28 minutes to it which will be 5: 28 in the evening.
  • Therefore, it will be 5:28 pm in the evening when it is 12:00 pm in London.

Monday, September 21, 2015 at 18:18:PM