Why is it 5:30 pm in India when it is 12 pm or noon in London?
India is located to the east of London (Greenwich).
The Earth rotates from west to east, completing 360° in 24 hours, which means 15° of longitude equals 1 hour of time.
India's standard meridian (82.5°E) is approximately 82.5° east of the Prime Meridian (0°) at Greenwich. This longitude difference of 82.5° corresponds to a time difference of 82.5° ÷ 15° per hour = 5.5 hours.
Since India is to the east, Indian time is ahead of London time by 5 hours 30 minutes. Therefore, when it is noon (12 pm) in London, it is 5:30 pm in India.
Explanation
The chapter explains that the Prime Meridian at Greenwich (0° longitude) is the reference point for time zones. Indian Standard Time (IST) is based on the meridian at 82.5°E, which is 5 hours 30 minutes ahead of Greenwich Mean Time (GMT). This is because India lies to the east of Greenwich, and places to the east experience time ahead of those to the west. The calculation is: 82.5° ÷ 15° per hour = 5.5 hours = 5 hours 30 minutes.
Solution Steps
Step 1: Identify India's standard meridian: 82.5°E
Step 2: Identify Greenwich meridian: 0°
Step 3: Calculate longitude difference: 82.5° - 0° = 82.5°
Step 4: Convert to time: 82.5° ÷ 15° per hour = 5.5 hours = 5 hours 30 minutes
Step 5: India is east of Greenwich, so Indian time is ahead