Class 6 Geography Notes Chapter 1 (The Earth in the Solar System) – The Earth Our Habitat

Read detailed notes for Chapter 1: The Earth in the Solar System from your NCERT Class 6 Geography textbook, 'The Earth Our Habitat'.

Chapter 1
The Earth in the Solar System

• Celestial Bodies:

  • All objects visible in the night sky are called celestial bodies.
  • Examples: The Sun, the Moon, stars, planets, asteroids, meteoroids.

• Stars:

  • Celestial bodies that are very big and hot.
  • Made up of gases.
  • Have their own heat and light, which they emit in large amounts.
  • The Sun is a star.
  • Stars appear small because they are very far away from us.

• Constellations:

  • Patterns formed by different groups of stars in the night sky.
  • Examples:
    • Ursa Major or Big Bear: One of the most easily recognizable constellations.
    • Saptarishi (Sapt=seven, rishi=sages): A group of seven stars, part of the Ursa Major constellation. It is easily identifiable.
  • Pole Star (North Star):
    • Indicates the north direction.
    • Remains in almost the same position in the sky.
    • Can be located with the help of the Saptarishi. Imagine a line joining the two pointer stars of Saptarishi and extend it further; it will point to the Pole Star.

• The Solar System:

  • The Sun, eight planets, satellites, and other celestial bodies like asteroids and meteoroids form the solar system.
  • We often call it a 'solar family' with the Sun as its 'Head'.

• The Sun:

  • Located at the center of the solar system.
  • It is huge and made up of extremely hot gases.
  • Provides the pulling force that binds the solar system together.
  • The ultimate source of heat and light for the entire solar system.
  • About 150 million kilometers away from the Earth.

• Planets:

  • Celestial bodies that do not have their own heat and light.
  • Lit by the light of the stars (like our Sun).
  • The word 'planet' comes from the Greek word "Planetai" meaning 'wanderers'.
  • There are eight planets in our solar system.
  • Order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
    • (Mnemonic: My Very Efficient Mother Just Served Us Nuts)
  • Orbit: All planets move around the Sun in fixed, elongated paths called orbits.
  • Mercury: Nearest to the Sun, takes about 88 days to complete one orbit.
  • Venus: Considered 'Earth’s-twin' because its size and shape are very similar to Earth's.
  • Pluto: Previously considered a planet, now classified as a "dwarf planet" by the International Astronomical Union (IAU) in 2006.

• The Earth:

  • The third nearest planet to the Sun.
  • The fifth largest planet in size.
  • Shape: Slightly flattened at the North and South poles and bulges slightly in the middle. This shape is described as a Geoid (meaning 'earth-like shape').
  • Unique Planet: Conditions favourable to support life are probably found only on Earth.
    • Not too hot, not too cold.
    • Has water and air (with life-supporting gases like oxygen).
  • Called the 'blue planet' because its two-thirds surface is covered by water, making it appear blue from outer space.

• The Moon:

  • Earth's only natural satellite.
  • Its diameter is only one-quarter that of the Earth.
  • Appears big because it is nearer to our planet than other celestial bodies (about 3,84,400 km away).
  • Moves around the Earth in about 27 days.
  • Takes exactly the same time to complete one spin on its axis.
  • As a result, only one side of the Moon is visible to us on Earth.
  • Does not have conditions favourable for life (no water, no air).
  • Has mountains, plains, and depressions (craters) on its surface which cast shadows, visible especially during a full moon.

• Satellites:

  • Celestial bodies that move around the planets in the same way as the planets move around the Sun.
  • Natural Satellites: Like the Moon orbiting Earth.
  • Human-made Satellites (Artificial Satellites):
    • Designed by scientists to gather information about the universe or for communication.
    • Carried by a rocket and placed in orbit around the Earth.
    • Examples of Indian satellites: INSAT, IRS, EDUSAT.

• Asteroids:

  • Numerous tiny bodies that also move around the Sun.
  • Found mainly between the orbits of Mars and Jupiter (this area is called the asteroid belt).
  • Scientists believe asteroids are parts of a planet which exploded many years back.

• Meteoroids:

  • Small pieces of rocks which move around the Sun.
  • Sometimes these meteoroids come near the Earth and tend to drop upon it.
  • During this process, due to friction with the air, they get heated up and burn, causing a flash of light (often called a 'shooting star' or meteor).
  • Sometimes, a meteoroid survives burning completely and falls to the Earth, creating a hollow. This unburnt piece is called a meteorite.

• Galaxy:

  • A huge system of billions of stars, and clouds of dust and gases.
  • Our solar system is part of a galaxy called the Milky Way Galaxy.
  • In ancient India, it was imagined to be a river of light flowing in the sky, thus named Akash Ganga.
  • Appears as a glowing white broad band across the sky on a clear starry night.

• The Universe:

  • There are millions of such galaxies that make up the Universe.
  • It is difficult to imagine how big the universe is; scientists are still trying to find out more about it.
  • We are just a tiny part of this vast universe (Earth -> Solar System -> Milky Way Galaxy -> Universe).

These notes cover the essential points discussed in Chapter 1. Remember to look at the diagrams and pictures in your textbook as they help visualize these concepts.