Geography Chapters

1. Continents and Oceans2. Biosphere3. Lithosphere4. Hydrosphere5. Atmosphere6. Latitudes and Longitudes7. Different Heat Zones of the Earth8. Longitudes and Time Zones9. International Date Line10. Motion of the Earth11. Effect of the Tilted Axis on Day and Night12. The Atmosphere (Composition and Layers)13. Weather and Climate14. Atmospheric Pressure15. Internal Structure of the Earth16. Rocks17. Earthquakes and Volcanoes18. Various Landforms (Mountains, Plateaus, Plains, Grasslands)19. Landforms Created by River System20. Landforms Created by Glacier21. Landforms Created by Wind22. Landforms Created by Groundwater23. The Indian Subcontinent Position, Extent, and Physical Features24. Climatic Diversity in the Indian Subcontinent25. Soil Resources of the Indian Subcontinent26. Agriculture in India27. Land Use Pattern of India28. Water Resources and Their Utilization in India29. Multipurpose River Valley Projects30. Transport in India31. Rivers of India

International Date Line (IDL)

“The International Date Line is the imaginary boundary where the calendar date changes by one day.”

What is the International Date Line?

The International Date Line (IDL) is an imaginary line located at approximately 180° longitude, opposite the Prime Meridian. It serves as the "line of demarcation" between two consecutive calendar days.

  • Not a straight line – it zigzags to avoid dividing countries and islands
  • Located mostly in the Pacific Ocean
  • Crossing it from east to west = gain a day
  • Crossing it from west to east = lose a day

How It Works

The IDL helps maintain a uniform global time-keeping system. Although it is 180° from the Prime Meridian, it deviates around territories to keep local times aligned with dates.

  • It separates one calendar day from the next
  • Countries near the IDL adjust their local time zones to avoid confusion
  • Line deviates around places like Kiribati, Samoa, and Russia’s Chukotka

Flow Diagram: International Date Line

Understanding the International Date Line
IDL ≈ 180° Longitude
⬇️
Zigzags to Avoid Territories
⬇️
Crossing East → West → Add a Day
⬇️
Crossing West → East → Subtract a Day

Important Facts

  • Located at 180° longitude (not fixed – deviates)
  • Not a part of any international law – followed by convention
  • Opposite of the Prime Meridian (0°)
  • Countries like Kiribati shifted the IDL to be the first to see sunrise
  • IDL is not the same as a time zone but affects date calculation

Previous Year Questions (PYQs)

  • SSC CHSL 2021: At which longitude is the International Date Line located?
  • 180°
  • SSC GD 2020: What happens when you cross the International Date Line from west to east?
  • One day is subtracted
  • RRB NTPC 2019: Why is the International Date Line not straight?
  • To avoid dividing nations or islands
  • SSC MTS 2018: The International Date Line passes through which ocean?
  • Pacific Ocean
  • HSSC CET 2022: What is the significance of the International Date Line?
  • It separates two calendar dates
  • SSC CGL 2020: If it is Monday west of the IDL, what day is it east of the line?
  • Tuesday
  • SSC JE 2019: What is the date difference on either side of the IDL?
  • One day
  • RRB Group D 2018: The IDL is used to regulate?
  • Change in date and time
  • SSC CPO 2017: Which country altered the IDL to celebrate the new millennium first?
  • Kiribati
  • SSC GD 2021: When a ship crosses the IDL from east to west, what happens?
  • A day is added
Tip: International Date Line ≠ Time Zone Line. It marks the date change, not the local time!
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