Question

For a difference of 1 degree longitude there is a time difference of 4 minutes.

Answer 1

The Earth rotates 360° in about 24 hours; this implies that it covers 15° in one hour or 1° in every four minutes. Thus, when it will be noon at Greenwich, the time at 15° east of Greenwich will be 60 minutes, i.e. 15 × 4 = 60 minutes. In other words, it will be one hour ahead of the Greenwich time, which means the time will be 1:00 pm. But at 15° west of Greenwich, the time will be one hour behind the Greenwich time. In other words, the time will be 11:00 am.