Longitude & Time

Longitude and time are closely interconnected due to the Earth’s rotation. Here’s how they relate:

Key Concepts:

1. Earth’s Rotation:
   • The Earth rotates 360° in 24 hours, which means it rotates 15° per hour.
   • This creates a direct relationship between longitude and time, where 1° of longitude equals 4 minutes of time (60 minutes ÷ 15° = 4 minutes per degree).
2. Time Zones:
   • The Earth is divided into 24 time zones, each spanning 15° of longitude.
   • The Prime Meridian (0° longitude), passing through Greenwich, England, is the reference point for Greenwich Mean Time (GMT).
   • Moving east of the Prime Meridian, time increases, while moving west, time decreases.
3. Local Time:
   • Local time at any place is determined by its longitude. For every degree east of Greenwich, local time is 4 minutes ahead, and for every degree west, it is 4 minutes behind.

Examples:

1. Longitude and Time Difference:
   • If a city is located at 75° East, its local time will be 5 hours ahead of GMT (75° ÷ 15° = 5 hours).
   • Similarly, a city at 90° West will be 6 hours behind GMT (90° ÷ 15° = 6 hours).
2. India’s Standard Time:
   • India uses Indian Standard Time (IST), which is based on the longitude 82.5° East.
   • IST is 5 hours and 30 minutes ahead of GMT (82.5° ÷ 15° = 5.5 hours).

This relationship between longitude and time is fundamental for navigation, timekeeping, and global coordination.