Hinglish

Local Time and Standard Time

Class 6 Social Science · Chapter 1: Locating Places on the Earth · NCERT Exploring Society: India and Beyond section 1.3

Learn

Meher's cousin Farhan lives in London. When Meher video-calls him at 6 in the evening after school, Farhan is just eating lunch! The Sun rises in the east first, so places to the east see sunrise, noon and sunset earlier.

The Earth turns a full circle (360°) in 24 hours. So it turns 15° every hour, or 1° every 4 minutes. For every 15° you go east, the local time is 1 hour ahead; for every 15° west, it is 1 hour behind.

Local time is based on the Sun at that exact place: noon when the Sun is highest. But if every town kept its own time, trains and offices would be confused! So a country picks one meridian for standard time. India uses 82.5°E (passing near Mirzapur in Uttar Pradesh): Indian Standard Time (IST) is 82.5 × 4 = 330 minutes, that is 5 hours 30 minutes ahead of Greenwich.

Big countries like Russia or the USA stretch across many meridians, so they use several time zones. India's east and west ends are about 2 hours apart in local time, yet the whole country follows one IST.

Explore: travel east and west.

  1. It is 12 noon at Greenwich. Find a place where it is 3:00 PM.
  2. Now find a place where it is 8:00 AM.
  3. Go to the meridian of IST (82.5°E) using 7.5° steps. What time is it there?

Remember

  • The Earth turns 15° every hour: going east, local time is ahead; going west, it is behind.
  • Indian Standard Time is based on 82.5°E and is 5 hours 30 minutes ahead of Greenwich.

Quick check

How many degrees does the Earth turn in one hour?

  1. 15°
  2. 24°
  3. 1°
  4. 60°
Answer

15°. 360° ÷ 24 hours = 15° per hour.

Think about it

Arunachal Pradesh sees sunrise almost 2 hours before Gujarat. Why might some people want a separate time zone for north-east India?

One answer

With IST, the sun rises and sets very early there, so a lot of daylight is used up before offices and schools open. A separate time zone could match the clock better to daylight, but one IST keeps things simple for the whole country.

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.