Introduction to Geography — Earth, Globe & Environment | CTET SST P2

Earth in the Solar System

The Sun, eight planets, their satellites, asteroids and meteoroids together form the Solar System. The Sun is the source of all heat and light. The eight planets in order from the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto, once counted as the ninth planet, was reclassified as a dwarf planet by the IAU in 2006 — NCERT Class 6 carries this update.

Mercury is the nearest to the Sun; Jupiter is the largest planet. Earth is the third planet from the Sun and is, so far, the only planet known to support life. Three conditions make Earth habitable: its distance from the Sun gives a moderate temperature range, the presence of liquid water, and a blanket of air containing oxygen.

Seen from space, Earth looks blue because two-thirds of its surface is covered by water — hence the name 'Blue Planet'. The Moon is the only natural satellite of the Earth. It is about 3,84,400 km away. The Moon's diameter is roughly one-fourth that of the Earth. It has no atmosphere, no water and no life. Because it rotates and revolves around the Earth in the same period (about 27 days), we always see the same face of the Moon.

Bodies smaller than planets that revolve around the Sun are called asteroids; most lie in a belt between Mars and Jupiter. Small pieces of rock that travel through space and sometimes enter Earth's atmosphere are meteoroids; the bright streak they make as they burn up is a 'shooting star'. Galaxies are vast collections of billions of stars; our galaxy is the Milky Way (Akash Ganga). The Universe is the totality of all galaxies. Teachers should keep the Sun-planet-satellite hierarchy explicit because CTET questions often test whether the candidate can place a body in the correct category.

Shape and Size of the Earth

Ancient people thought the Earth was flat. Greek thinkers like Pythagoras and Aristotle reasoned that it was spherical because of the curved shadow Earth casts on the Moon during a lunar eclipse and because ships disappear hull-first below the horizon. Photographs from space in the 20th century settled the matter.

Strictly, the Earth is not a perfect sphere. Because of its rotation it is slightly flattened at the poles and bulges at the Equator. This shape is called an oblate spheroid or geoid. The polar diameter (about 12,714 km) is shorter than the equatorial diameter (about 12,756 km) by about 42 km. The equatorial circumference is approximately 40,075 km.

Earth's size matters for life. If it were much smaller — like Mercury — its weak gravity could not hold an atmosphere. If much larger — like Jupiter — gravity would be so strong that no land animal could stand upright. Earth's mass and gravity hold a thin layer of gases close to the surface: this is the atmosphere that protects us from harmful radiation and traps heat to keep the planet warm.

The model of the Earth used in classrooms is the globe. A globe shows the true shape (a sphere) and the correct relative size of land and water; it is the most accurate representation. However, it cannot be carried in a pocket and one cannot see the whole Earth at once. That is why maps, which flatten the curved surface onto paper, are used alongside the globe. Every flat map distorts either shape, area, distance or direction; a globe distorts none of these. CTET regularly tests two facts here — that Earth is an oblate spheroid (not a perfect sphere) and that the globe is the most accurate model. Teachers should pair the globe with an orange or a ball during the first lesson so the abstraction becomes physical.

Latitudes and Longitudes

To locate a place on the Earth's surface we use an imaginary grid of horizontal and vertical lines drawn on the globe. The horizontal lines are parallels of latitude; the vertical lines are meridians of longitude.

The Equator is the most important parallel — a great circle that divides the Earth into the Northern and Southern Hemispheres. It is labelled 0°. From the Equator, latitudes are measured up to 90° North (the North Pole) and 90° South (the South Pole). Four other latitudes are specially named: the Tropic of Cancer (23½° N), the Tropic of Capricorn (23½° S), the Arctic Circle (66½° N) and the Antarctic Circle (66½° S). The area between the two tropics receives vertical Sun rays at least once a year and is called the Torrid Zone. The areas between the tropics and the polar circles are the Temperate Zones, and beyond the polar circles lie the Frigid Zones.

Longitudes run from pole to pole. The Prime Meridian (0°) passes through Greenwich, near London, and divides the Earth into the Eastern and Western Hemispheres. From 0° we count 180° East and 180° West, which meet on the opposite side of the globe at the International Date Line. Crossing the IDL from west to east means losing a day; from east to west means gaining a day.

Each degree of longitude equals 4 minutes of time (Earth turns 360° in 24 hours, so 15° per hour). India's standard meridian is 82½° E passing through Mirzapur in Uttar Pradesh, and Indian Standard Time is therefore 5 hours 30 minutes ahead of Greenwich Mean Time (GMT). Teachers should give children a simple coordinate exercise — locate Delhi (~28° N, 77° E), Mumbai (~19° N, 73° E), Kolkata (~22° N, 88° E) — so latitude-longitude reading becomes an automatic skill.

Motions of the Earth — Rotation and Revolution

Earth has two principal motions. Rotation is the spinning of the Earth on its own axis from west to east. One full rotation takes 24 hours (one day). The axis is an imaginary line passing through the North and South Poles and is tilted at an angle of 23½° from the perpendicular to the orbital plane. This tilt, not the rotation itself, is what produces the seasons.

The revolution is the movement of the Earth around the Sun in a slightly elliptical orbit. One revolution takes 365 days and about 6 hours — usually counted as 365 days. The extra six hours add up to 24 hours (one full day) every four years, which is added to February in a leap year, making it 29 days long. A leap year therefore has 366 days. The year 2024 was a leap year; 2028 will be the next.

The plane in which the Earth revolves is called the orbital plane. Because the axis is tilted and points to the same star (Polaris) throughout the year, different parts of the Earth lean towards the Sun at different times. Around 21 June the Northern Hemisphere is tilted towards the Sun — this is the summer solstice. Around 22 December the Southern Hemisphere is tilted towards the Sun — the winter solstice for the North. On 21 March and 23 September the Sun shines vertically on the Equator; day and night are equal everywhere. These are the equinoxes (spring and autumn).

The combination of rotation, revolution and axial tilt explains four phenomena every CTET candidate must be able to list: (1) day and night, (2) variation in length of day across the year, (3) the four seasons, and (4) the existence of leap years.

Day, Night and Seasons

The Earth is illuminated by the Sun, but at any moment only one half faces the Sun. Because the Earth rotates from west to east, the half-facing-the-Sun keeps changing. The half facing the Sun has day; the half facing away has night. The imaginary line separating the lit and unlit halves is the circle of illumination. If the Earth did not rotate, one half would have endless day and the other endless night — life would be impossible.

The length of day and night is not equal everywhere. Only on the Equator are they always 12 hours each. At latitudes farther from the Equator the difference becomes larger and larger. Beyond the Arctic and Antarctic Circles there are days with continuous sunlight in summer and continuous darkness in winter — the so-called midnight Sun and polar night.

The seasons arise from the tilt of Earth's axis combined with revolution, not from the small change in distance from the Sun. When the Northern Hemisphere is tilted towards the Sun (around June), it receives sunlight at a steeper angle, days are longer and the season is summer. The opposite hemisphere experiences winter. The reverse happens in December. Around the equinoxes the Sun is vertically over the Equator; days and nights are nearly equal across the globe and we experience the transitional spring and autumn seasons.

India, lying mostly between the Equator and the Tropic of Cancer, has its own characteristic cycle — summer (March–May), the south-west monsoon (June–September), the retreating monsoon (October–November) and winter (December–February). A common misconception, frequently tested in CTET, is that 'summer happens because the Earth is closer to the Sun'. Teachers should challenge this by showing that when the Northern Hemisphere has summer, the Southern Hemisphere has winter — even though both hemispheres are at the same distance from the Sun. The tilt of the axis, not the elliptical orbit, is the cause.

The Globe vs the Map

A globe is a true three-dimensional model of the Earth. It shows the correct shape (oblate spheroid), the correct relative areas of continents and oceans, and the correct directions and distances. The globe is the only representation that does not distort the Earth. However, it is bulky, only one half can be seen at a time, and details cannot be enlarged.

A map is a representation of the Earth, or part of it, drawn on a flat surface to a definite scale. Maps can be carried in the pocket, opened on a desk and made for any required scale — a city street, a district, India, or the whole world. The cost of flattening a curved surface, however, is distortion: every flat map distorts at least one of shape, area, distance or direction.

Three essential elements appear on every good map — the title (what the map shows), the direction (a north arrow; by convention north is at the top), the scale (the ratio between distance on the map and the corresponding distance on the ground) and a legend or key (explaining the symbols used). Maps that show physical features such as mountains, plateaus, plains and rivers are called physical maps. Maps that show countries, states and cities with their boundaries are political maps. Maps that show specific information — rainfall, roads, soils, population, industries — are thematic maps.

For classroom practice, students should learn to read a map with the convention North-up, East-right, South-down, West-left (NEWS), identify symbols from the legend, and use the scale to measure rough distances. A common CTET-level question contrasts the globe and the map; the answer is that the globe is the most accurate but least portable, while the map is portable and customisable but always distorts. Both are essential — they complement each other.

The Four Realms of the Earth

The Earth's environment is conventionally divided into four realms — the lithosphere (solid land), the hydrosphere (all water), the atmosphere (air) and the biosphere (the zone where life exists).

The lithosphere is the solid crust of the Earth — continents, mountains, plateaus, plains and the ocean floor. It is the source of soil, minerals, fossil fuels and building materials. Tectonic activity within the lithosphere produces earthquakes, volcanoes and the slow drift of continents.

The hydrosphere covers about 71% of the Earth's surface. Of all this water, about 97% is the saline water of oceans and seas; only about 3% is freshwater, and most of that is locked in glaciers and polar ice caps. Less than 1% of the Earth's water is available as liquid freshwater in rivers, lakes and underground aquifers — a critical fact for water-conservation lessons.

The atmosphere is the thin envelope of gases held by Earth's gravity. About 78% is nitrogen, 21% oxygen, and the remaining 1% is argon, carbon dioxide, water vapour and trace gases. The atmosphere shields the Earth from harmful ultraviolet radiation (through the ozone in the stratosphere), traps the right amount of heat (the greenhouse effect) and provides the oxygen we breathe.

The biosphere is the narrow zone of contact between land, water and air where all life — plants, animals, micro-organisms and human beings — exists. It is the realm in which the other three realms come together and support life. The four realms are not separate compartments; they constantly exchange matter and energy. The water cycle, for example, moves water from the hydrosphere to the atmosphere to the lithosphere and back. Understanding the four realms gives children a framework for the chapters that follow — soil, water, air, vegetation and wildlife.

Teaching Geography — Globe and Maps

Geography is best taught as a concrete-to-abstract subject. NCF 2005 recommends that learners begin from their own neighbourhood and gradually extend outward to the district, state, country and world. The principle of 'near to far' and 'known to unknown' applies directly: before children read a world map they should sketch their own classroom, then their school, then their locality.

The globe should be physically present in every upper-primary classroom. Activities such as locating the Equator with a piece of string, pasting a sticker on one's own city, simulating rotation with a torch and a globe in a dark room (one half lit, one half in shadow), and tilting the axis to demonstrate seasons make abstract concepts visible. The torch-and-globe demonstration is the single most effective way to break the misconception that seasons depend on distance from the Sun.

Maps should be introduced through the four essentials — title, direction (North arrow), scale and legend. Start with a sketch map of the classroom drawn 'not to scale', then introduce scale through a simple field measurement. Different map types — physical, political and thematic — should be compared side by side. Encouraging children to make their own thematic maps (a rainfall map of India coloured from a data table, a road map of their village) builds map literacy faster than passive reading.

Local field trips, hand-drawn cross-sections, sand-tray models of rivers and mountains, satellite images from Bhuvan or Google Earth, and weather observation diaries connect textbook geography to lived experience. Assessment in geography should go beyond memorising capitals; it should test map reading, direction, drawing of cross-sections, and interpretation of pictures, photographs and data tables. The CTET pedagogy questions in this chapter usually reward the option that emphasises observation, activity and field experience over rote learning.