Source: The Earth: Our Habitat – Textbook of Social Science (Geography), Class VI, Pages 10–17 Class: VI
Section 1. The Globe 🌍
🔑 Globe = A true model (miniature form) of the earth.
- Earth is slightly flattened at the North and South Poles and bulges in the middle.
- The globe is not fixed – it can be rotated (like a top spin or potter's wheel).
- Countries, continents and oceans are shown in their correct size on the globe.
Section 2. Key Reference Lines and Points 🌍
| Term | Definition | Key Fact |
|---|
| Axis | Needle fixed through the globe in a tilted manner | Imaginary line on the real earth – no actual needle |
| North Pole / South Pole | Two points through which the axis passes | Globe moves west to east around this axis |
| Equator | Imaginary line dividing the globe into two equal halves | 0° latitude – most important reference point |
| Northern Hemisphere | Northern half of the earth (above equator) | One of two equal halves |
| Southern Hemisphere | Southern half of the earth (below equator) | One of two equal halves |
Section 3. Latitudes – Parallels of Latitude 🌍
🔑 Parallels of Latitudes = All parallel circles from the equator up to the poles. Measured in degrees.
| Fact | Detail |
|---|
| Equator | 0° latitude |
| North Pole | 90°N latitude |
| South Pole | 90°S latitude |
| North of equator | Called north latitudes – marked N |
| South of equator | Called south latitudes – marked S |
| Size of parallels | Decreases as we move away from equator |
Example: Chandrapur (India) = 20°N | Belo Horizonte (Brazil) = 20°S – same parallel number, opposite hemispheres.
🎯 By measuring the angle of the Pole Star from your place, you can know the latitude of your place.
Section 4. Important Parallels of Latitudes 🌍
| Parallel | Value | Hemisphere |
|---|
| Tropic of Cancer | 23½°N | Northern |
| Tropic of Capricorn | 23½°S | Southern |
| Arctic Circle | 66½°N | Northern |
| Antarctic Circle | 66½°S | Southern |
Section 5. Heat Zones of the Earth 🌍
| Heat Zone | Boundaries | Temperature | Reason |
|---|
| Torrid Zone | Tropic of Cancer to Tropic of Capricorn | Maximum heat | Mid-day sun overhead at least once a year |
| Temperate Zones (N + S) | Tropic of Cancer to Arctic Circle (N); Tropic of Capricorn to Antarctic Circle (S) | Moderate | Sun never overhead; rays increasingly slanted |
| Frigid Zones (N + S) | Arctic Circle to North Pole (N); Antarctic Circle to South Pole (S) | Very cold | Sun never rises much above horizon; rays always slanting |
⚙️ Slanted rays spread over a larger area → less heat per unit area. Direct rays concentrate heat on smaller area → more heat. (Source: Torch-light analogy, Figures 2.4a/b)
Section 6. Longitudes – Meridians of Longitude 🌍
🔑 Meridians of Longitude = Semi-circles running from North Pole to South Pole. Measured in degrees (further divided into minutes and seconds).
- Distance between meridians decreases towards the poles – becomes zero where all meridians meet.
- All meridians are of equal length (unlike parallels).
- Counting begins from the Prime Meridian (0°) – passes through Greenwich, British Royal Observatory.
- Count goes 180° eastward and 180° westward from Prime Meridian.
- 180°E and 180°W are the same line.
- Prime Meridian + 180° meridian divide earth into Eastern Hemisphere (E) and Western Hemisphere (W).
Section 7. The Grid 🌍
🔑 Grid = Network of parallels of latitudes and meridians of longitudes. Used to locate any point on the globe.
Example: Dhubri (Assam) = 26°N, 90°E – find where these two lines intersect on the globe.
Section 8. Longitude and Time 🌍
- Sun is the best natural time-keeper. Local time = reckoned by shadow cast by the sun (shortest at noon).
- Earth rotates 360° in 24 hours → 15° per hour → 1° per 4 minutes.
- Places east of Greenwich = ahead; places west = behind.
| Position | Time when it is 12 noon at Greenwich |
|---|
| 15°E | 1:00 p.m. (1 hour ahead) |
| 15°W | 11:00 a.m. (1 hour behind) |
| 180° | Midnight |
- All places on the same meridian share the same local time.
Section 9. Standard Time 🌍
🔑 Standard Time = Local time of a country's central meridian, adopted as uniform time for the whole country.
Need: Local times differ on different meridians – impractical for train timetables and daily life.
| Detail | Value |
|---|
| India's Standard Meridian | 82½°E (82°30'E) |
| India's Standard Time | Indian Standard Time (IST) |
| IST ahead of GMT | 5 hours 30 minutes |
- Earth divided into 24 time zones of 1 hour each – each zone covers 15° of longitude.
- Russia has eleven standard times (largest longitudinal extent example).
Common Confusions ⚠️
| Confusion | Clarification |
|---|
| Latitude vs Longitude | Latitudes = horizontal circles (N/S of equator). Longitudes = vertical semi-circles (E/W of Prime Meridian). |
| Parallels vs Meridians | Parallels decrease in size towards poles. Meridians are all equal length, meeting at poles. |
| Equator vs Prime Meridian | Equator (0° lat) → N/S Hemispheres. Prime Meridian (0° long) → E/W Hemispheres. |
| Prime Meridian value | Always 0° – not 90°. North Pole = 90°N. These are different things. |
| 180°E and 180°W | Same line – not two separate meridians. |
Memory Aids 💡
| What to Remember | Mnemonic / Trick |
|---|
| Latitude lines run east–west | 💡 LAT = LATeral – flat rungs across the globe like a ladder |
| Longitude lines run north–south | 💡 LONG = LONG drop – fall from North Pole to South Pole |
| Cancer = North, Capricorn = South | 💡 C before Ca – Cancer comes first in alphabet, sits above equator (North) |
| Earth rotates 15° per hour | 💡 15 × 24 = 360 – one full circle in one full day |
| IST = GMT + 5½ hours | 💡 India is "5½ steps ahead" – add 5 hours 30 minutes to London time |
Exam Corner 🎯
Directly from The Earth: Our Habitat Exercise, Pages 16–17:
| Question | Topic | Reference |
|---|
| Q1(a) – True shape of the earth? | Shape of earth | Page 10 |
| Q1(b) – What is a globe? | Globe definition | Page 10 |
| Q1(c) – Latitudinal value of Tropic of Cancer? | Important parallels | Page 11 |
| Q1(d) – Three heat zones of the Earth? | Heat zones | Pages 12–13 |
| Q1(e) – Parallels of latitude and meridians of longitude? | Definitions | Pages 11–13 |
| Q1(f) – Why does torrid zone receive maximum heat? | Heat zones – reason | Page 12 |
| Q1(g) – Why 5:30 p.m. in India when noon in London? | IST / Standard time | Page 15 |
| Q2(a) – Value of Prime Meridian → (ii) 0° | Prime Meridian | Page 13 |
| Q2(b) – Frigid zone lies near → (i) the Poles | Frigid zone | Page 13 |
| Q2(c) – Total number of longitudes → (i) 360 | Longitudes | Page 13 |
| Q2(d) – Antarctic Circle located in → (ii) Southern hemisphere | Antarctic Circle | Page 11 |
| Q2(e) – Grid is a network of → (i) parallels of latitudes and meridians of longitudes | Grid | Page 13 |
| Q3(a) – Tropic of Capricorn located at | 23½°S | Page 11 |
| Q3(b) – Standard Meridian of India | 82½°E (82°30'E) | Page 15 |
| Q3(c) – 0° Meridian also known as | Prime Meridian | Page 13 |
| Q3(d) – Distance between longitudes decreases towards | The poles | Page 13 |
| Q3(e) – Arctic Circle located in the __ hemisphere | Northern | Page 11 |
Abbreviation Legend
| Abbreviation | Full Form |
|---|
| IST | Indian Standard Time |
| GMT | Greenwich Mean Time |
| N / S / E / W | North / South / East / West |
