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The Earth in Space

Photo Credit: ThePlanets.org

  • The word ‘solar’ is derived from the Latin word ‘solus’ which means ‘sun’.
  • The solar system is made up of the sun and the nine planets, even though there is a disagreement about Pluto being a planet.
  • These planets (from the nearest to the sun and moving outwards) are:
    • Mercury
    • Venus
    • Earth
    • Mars
    • Jupiter
    • Saturn
    • Uranus
    • Neptune
    • Pluto
  • Venus is the brightest planet.
  • Pluto is the coldest planet.
  • Mercury is the hottest because it is the nearest to the sun.
  • All these planets revolve around the sun, each on its own orbit.
The Earth
  • This is the planet known to contain living things.
  • It is made up of the lithosphere (solid part), the hydrosphere (part of the earth covered by water, like seas and oceans), and the atmosphere (gaseous envelope).
  • The atmosphere is made up of these gases:
    • Nitrogen (78.1% of dry air, by volume)
    • Oxygen (20.95% of dry air, by volume)
    • Carbon IV oxide (0.04% of dry air, by volume)
    • Argon (0.93% of dry air, by volume)
    • Water vapor (variable)
  • Beyond the atmosphere, there is a space with no air or other matter. This space is called outer space.
Composition of the Earth
  • Atmosphere
  • Hydrosphere
  • Crust
  • Mantle
  • Core

Layers of the Earth (Photo Credit: PhysicalGeography.net)

Movements of the Earth
  • The earth carries out two types of movements:
    • Rotation – This is the movement of the earth on its axis.
    • Revolution – This is the movement of the earth along its orbit round the sun.
  • The earth completes one rotation in 24 hours.
  • The rotation of the earth causes day and night.
  • The revolution of the earth brings about the seasons of the year.

Rotation and Revolution of the Earth (Photo Credit: Google.com)

Zones of the Atmosphere

Zones of the Atmosphere (Photo Credit: Scied.ucar.edu)

Zone Characteristics
Troposphere The air is dense
Stratosphere The air is less dense
Mesosphere The air is thin
Ionosphere Gas molecules are ionized
Eclipse and Seasons of the Year
  • The sun is a star at the center of our solar system.
  • It is larger than the earth, and is made up of hot gases which produce a lot of heat and light.
  • The light from the sun enables us to see on earth.
  • Green plants also make use of the sun light to make their food through a process called photosynthesis.
  • The warmth from the sun keeps plants and animals alive.
  • The moon is the earth’s satellite, i.e., it always revolves round the earth.
  • The moon’s surface is uneven and consists of hills and valleys called craters.
  • There is no air and no life on the moon.
  • The moon completes one revolution round the earth in 28 days. This period of 28 days is called one lunar month.
  • The moon does not shine its own light. Moon light is actually sun light reflected from the surface of the moon.
  • The changes observed in the sun lit parts of the moon at different times are called phases of the moon. These phases of the moon are:
    • New moon.
    • Quarter moon.
    • Half moon.
    • Three-quarter moon.
    • Full moon.
  • It is possible for the moon to shield or eclipse the earth from the sun because of the movements of the moon and the earth.
  • There are two types of eclipses. They are:
    • Eclipse of the Sun (Solar Eclipse): This happens when the moon moves in between the earth and the sun.
    • Eclipse of the Moon (Lunar Eclipse): This happens when the earth comes between the sun and the moon so that the moon is in the shadow of the earth.

Lunar and Solar Eclipse (Photo Credit: Dyer Observatory)

Season of the Year
  • The climate of a place is the typical weather condition of the place.
  • A season is a period of time in the year which has distinctive characteristics, e.g. rainy season is when there is a lot of rain.
  • The revolution of the earth causes the occurrence of seasons.
  • As the earth moves around the sun, all parts of the earth do not receive the same number of sunshine at the same time. When the earth is in a particular part of the orbit round the sun, an area of the earth, say Europe, will have sunshine while the part opposite it may have total darkness.
  • In the Northern and Southern zones of the earth, there are four seasons;
    • Summer.
    • Autumn.
    • Winter.
    • Spring.

Seasons of Earth (Photo Credit: Enchantedlearning.com)

  • In West Africa, there are only two seasons;
    • Rainy season.
    • Dry season.
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