Class 6 Geography Notes Chapter 2 (Globe: Latitudes and Longitudes) – The Earth Our Habitat

Get detailed notes for Chapter 2: Globe: Latitudes and Longitudes from the NCERT Class 6 Geography textbook 'The Earth Our Habitat'. These notes are structured for government exam preparation.

Chapter 2
Globe: Latitudes and Longitudes

1. The Globe

• A globe is a true model (miniature form) of the Earth.
• It shows the shape of the Earth, continents, oceans, and countries in their correct relative sizes and locations.
• Globes can be of varying sizes.
• A globe is not fixed; it can be rotated, just like the Earth spins.
• Axis: An imaginary line passing through the centre of the Earth, connecting the North Pole and the South Pole. The Earth rotates around this axis. The globe is tilted on its stand, representing the tilt of the Earth's axis (approximately 23 ½° from the vertical or 66 ½° from the orbital plane).
• Poles: Two points on the globe through which the axis passes – the North Pole (N) and the South Pole (S).

2. Latitudes (Parallels of Latitude)

• Equator: An imaginary circular line running on the globe that divides it into two equal halves. It is the most important parallel of latitude.
  • Represents the 0° latitude.
  • The northern half of the Earth is known as the Northern Hemisphere.
  • The southern half is known as the Southern Hemisphere.
• Parallels of Latitude: All imaginary parallel circles running from the Equator towards the poles.
  • Measured in degrees (°).
  • The Equator is 0°. The distance from the Equator to either pole is one-fourth of a circle round the Earth, i.e., ¼ of 360°, which is 90°.
  • Thus, 90° North latitude marks the North Pole, and 90° South latitude marks the South Pole.
  • All parallels north of the Equator are called North latitudes (indicated by N).
  • All parallels south of the Equator are called South latitudes (indicated by S).
  • Parallels decrease in size as we move away from the Equator towards the poles.

3. Important Parallels of Latitude

• Besides the Equator (0°), the North Pole (90° N), and the South Pole (90° S), there are four other important parallels:
  • (i) Tropic of Cancer: Located at 23 ½° N in the Northern Hemisphere.
  • (ii) Tropic of Capricorn: Located at 23 ½° S in the Southern Hemisphere.
  • (iii) Arctic Circle: Located at 66 ½° N, north of the Equator.
  • (iv) Antarctic Circle: Located at 66 ½° S, south of the Equator.

4. Heat Zones of the Earth

• Based on the heat received from the Sun, the Earth is divided into three main Heat Zones, defined by the important parallels of latitude:
  • (i) Torrid Zone:
    • Area between the Tropic of Cancer (23 ½° N) and the Tropic of Capricorn (23 ½° S).
    • Receives the maximum heat because the midday sun is exactly overhead at least once a year on all latitudes within this zone.
  • (ii) Temperate Zones:
    • North Temperate Zone: Area between the Tropic of Cancer (23 ½° N) and the Arctic Circle (66 ½° N).
    • South Temperate Zone: Area between the Tropic of Capricorn (23 ½° S) and the Antarctic Circle (66 ½° S).
    • These zones experience moderate temperatures.
    • The midday sun never shines directly overhead on any latitude beyond the Tropics. The angle of the sun's rays decreases towards the poles.
  • (iii) Frigid Zones:
    • North Frigid Zone: Area between the Arctic Circle (66 ½° N) and the North Pole (90° N).
    • South Frigid Zone: Area between the Antarctic Circle (66 ½° S) and the South Pole (90° S).
    • These zones are very cold.
    • The sun does not rise much above the horizon, and its rays are always slanting, providing less heat.

5. Longitudes (Meridians of Longitude)

• Meridians of Longitude: Imaginary lines (semi-circles) running from the North Pole to the South Pole.
  • Used to locate places east or west.
  • The distance between them decreases steadily towards the poles until it becomes zero at the poles, where all meridians meet.
  • Unlike parallels of latitude, all meridians are of equal length.
• Prime Meridian: The meridian which passes through Greenwich, where the British Royal Observatory is located.
  • Its value is 0° longitude.
  • It divides the Earth into the Eastern Hemisphere and the Western Hemisphere.
• Measurement: Longitudes are measured in degrees (°).
  • We count 180° eastward and 180° westward from the Prime Meridian.
  • Longitudes to the east are indicated by E, and those to the west by W.
  • The 180° East and 180° West meridians are the same line.
• Grid System: The network formed by the parallels of latitude and meridians of longitude on the globe. This grid helps in locating any point on the globe accurately. Example: Dhubri in Assam is situated at 26° N latitude and 90° E longitude.

6. Longitude and Time

• The best means of measuring time is by the movement of the Earth, Moon, and planets. The Sun regularly rises and sets daily.
• Local Time: When the Prime Meridian of Greenwich has the sun at the highest point in the sky, all places along this meridian will have mid-day or noon. This is the local time for that meridian.
• Earth's Rotation and Time Calculation:
  • The Earth rotates 360° in about 24 hours.
  • This means it rotates 15° in 1 hour (360° / 24 hours = 15°/hour).
  • Or, it rotates 1° in 4 minutes (60 minutes / 15° = 4 minutes/degree).
• Time Zones:
  • As the Earth rotates from west to east, places east of Greenwich are ahead of Greenwich Mean Time (GMT).
  • Places west of Greenwich are behind GMT.
  • Example: At 15° East of Greenwich, the time is 15 x 4 = 60 minutes (1 hour) ahead of GMT. So, if it is 12 noon at Greenwich, it is 1 PM at 15° E.
  • Example: At 15° West of Greenwich, the time is 1 hour behind GMT. So, if it is 12 noon at Greenwich, it is 11 AM at 15° W.
  • At 180° meridian, it will be midnight when it is noon at Greenwich.

7. Standard Time

• Why Standard Time? Countries often span several longitudes, leading to different local times within the country. This can cause inconvenience (e.g., preparing train timetables).
• Standard Meridian: Most countries adopt the local time of a central meridian passing through the country as the standard time for the whole country.
• Indian Standard Time (IST):
  • India's longitudinal extent is wide (approx. 68° E to 97° E).
  • The Standard Meridian of India is 82 ½° E (or 82°30' E). It passes through Mirzapur in Uttar Pradesh.
  • The local time at this meridian is taken as the Indian Standard Time (IST) for the whole country.
  • IST Calculation: India is located east of Greenwich at 82°30' E.
    • Time difference = 82.5 * 4 minutes = 330 minutes.
    • 330 minutes = 5 hours and 30 minutes (330 / 60).
    • Therefore, IST is 5 hours and 30 minutes ahead of GMT. (Example: If it is 12:00 noon GMT, it is 5:30 PM IST).
• Some countries with a large east-west extent adopt more than one standard time (e.g., Russia).

This covers the essential points from Chapter 2 for exam preparation. Remember to visualize these concepts using a globe or map for better understanding.