CBSE Notes For Class 6 Geography Social Science Chapter 3 Motions of the Earth
Types of Motion of the Earth
Earth has two types of motion i.e. Rotation and Revolution.
Rotation of the Earth: Rotation is the movement of the Earth on its axis. The axis of the Earth (an imaginary line) makes an angle of 66 ½0 with its orbital plane. The plane formed by the orbit is known as the orbital plane.
- The Earth takes about 24 hours to complete one rotation around its axis. The period of rotation is known as the Earthday. This is the daily motion of the Earth.
- Only half of the sunlight is received by the Earth at a time due to its spherical shape. The part of the Earth facing the Sun experiences day while the other half away from the Sun experiences night.
- The circle that divides day from night on the Earth is called the circle of illumination.
Revolution of Earth: Revolution is the movement of the Earth around the Sun in a fixed path or orbit.
- The Earth takes 365 days (one year) and 6 hours to revolve around the Sun. The Earth revolves around the Sun in an elliptical orbit and during this movement, the Earth is inclined in the same direction.
- The time of 6 hours is ignored for the sake of convenience and only a year is considered. The time of 6 hours saved every year is added to make one day (24 hours) over the span of four years.
- This extra day is added to the month of February, thus in every fourth year, February is of 29 days instead of 28 days. The year with 366 days is called a leap year.
- If the Earth does not rotate, the part of the Earth facing the Sun would always experience day, thus bringing continuous warmth to the region. The other part of the Earth would remain in darkness and be freezing cold all the time. Life would not have been possible in such extreme conditions.
- Day and Night on the Earth due to Rotation
Knowledge Plus: The ancient Indian astronomer Aryabhatta had stated that ‘the Earth is round and rotates on its own axis.
CBSE Notes For Class 6 Geography Chapter 3 Seasons
- The change in season is caused due to the change in the position of the Earth around the Sun.
- On the basis of change in the position of Earth, a year is divided into summer, winter, spring, and autumn.
Summer Solstice: On 21st June, the Northern Hemisphere is tilted towards the Sun and the rays of the Sun fall directly on the Tropic of Cancer. This position of the Earth is called the summer solstice.
- During this position, the areas in the Northern Hemisphere receive more heat. On the other hand, areas near the poles receive less heat as the rays of the Sun are slanting.
- The places beyond the Arctic Circle experience continuous daylight for about six months. As the larger portion of the Northern Hemisphere gets light from the Sun, it is summer in the regions in the North of the equator.
- In these regions, The longest day and shortest night occur on the 21st of June. On the other hand, the Southern Hemisphere experiences winter, and the nights are longer than the days.
Knowledge Plus: In Australia, Christmas is celebrated in the summer season.
Winter Solstice: On 22nd December, the South Pole tilts towards the Sun, and the Tropic of Capricorn receives direct rays of the Sun. This position of the Earth is called winter solstice.
- At this position, a larger part of the Southern Hemisphere gets light and it is summer in this hemisphere with longer days and shorter nights.
- On the other hand, the Northern Hemisphere experiences winter with shorter days and longer nights.
Spring and Autumn: On 21st March, it is spring in the Northern Hemisphere and autumn in the Southern Hemisphere. On 23rd September, it is autumn season in the Northern Hemisphere and spring season in the Southern Hemisphere.
Equinox: On 21st March and 23rd September, the Sunray falls directly on the equator. At this position, neither of the poles is tilted toward the Sun. Thus, the whole Earth experiences equal days and equal nights. This is called an equinox.
