Motions of the Earth Summary Class 6 Social Science Chapter 3

 The earth has two types of motions

1. Rotation 
2. Revolution.

• Rotation is the movement of the earth on its axis.
• The movement of the earth around the sun in a fixed path or orbit is called Revolution.
• Orbital plane: The axis of the earth which is an imaginary line, makes an angle of 66½° with its orbital plane. The plane formed by the orbit is known as the orbital plane.
• Tilt of Axis: Earth’s axis is tilted at an angle of 66.5oon its orbital plane. On the other hand; the earth’s axis is tilted at 23.5o on the line which is perpendicular to its orbital plane.
• The circle that divides the day from night on the globe is called the circle of illumination.
• The earth takes about 24 hours to complete one rotation around its axis. 
  • The period of rotation is known as the earth day means daily motion of the earth.
• The time taken by the earth to complete one revolution is called one year. 
• One year has 365 and ¼ days (365 days and 6 hours).

What Would Happen if the Earth Did Not Rotate?

• If there had been no rotation of the earth; one half of the earth would have been constantly in daylight and another half would have been constantly in dark. 
• The portion under sunlight would have been too hot. 
• On the other hand, the portion in dark would have been freezing cold. 
• Such extremes of temperature could have made it impossible for life to thrive on our planet.
• Perihelion: The point at which a planet is nearest to the sun is called perihelion.
• Aphelion: The point at which a planet is farthest from the sun is called aphelion.
• On 21st March and 23rd September, direct rays of the sun fall on the equator. At this position, neither of the poles is tilted towards the sun; so, the whole earth experiences equal days and equal nights. This is called an equinox.

Summer Solstice

• On 21st June, the Northern Hemisphere is tilted towards the sun. The rays of the sun fall directly on the Tropic of Cancer. As a result, these areas receive more heat.
• The areas near the poles receive less heat as the rays of the sun are slanting. The North Pole is inclined towards the sun and the places beyond the Arctic Circle experience continuous daylight for about six months.
• Since a large portion of the Northern Hemisphere is getting light from the sun, it is summer in the regions north of the equator.
• The longest day and the shortest night at these places occur on 21st June. At this time in the Southern Hemisphere all these conditions are reversed. It is winter season there. 
• The nights are longer than the days.

Winter Solstice

• On 22nd December, the Tropic of Capricorn receives direct rays of the sun as the South Pole tilts towards it. 
• As the sun’s rays fall vertically at the Tropic of Capricorn (23½° S), a larger portion of the Southern Hemisphere gets light. Therefore, it is summer in the Southern Hemisphere with longer days and shorter nights.
• The reverse happens in the Northern Hemisphere.