WBBSE Class 9 Geography And Environment Chapter 2 Movements Of The Earth Notes

WBBSE Chapter 2 Movements Of The Earth Salient Points Introduction

Every planet in the solar system rotates on its axis and revolves around the Sun.

The speed of rotation of Venus is less than the other planets of the solar system (equal to 243 Earth days).

The main statement of the Geocentric Theory is that the Sun and the planets are moving around the Earth. Although, now this concept has been proved wrong.

According to the Heliocentric Theory, the planets are moving around the Sun.

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The main proponents of Heliocentric Theory were Nicolaus Copernicus, Galileo, and Kepler.

In 1687, Sir Isaac Newton proved by his law of gravity that the Earth has two. motions-rotation and revolution, which are in action simultaneously.

The average distance of the Earth from the Sun is 150 million km.

Understanding Earth’s Rotation and Revolution

In 1851, Leon Foucault, a French physicist, demonstrated an experiment at Pantheon Church in Paris, France to prove the rotation of the Earth.

The speed of the Earth’s rotation is different at the different latitudes, 1675 km/hr at the Equator, 1533 km/hr at the Tropic of Cancer and Capricorn, 666 km/hr at both the Arctic and Antarctic Circle, and 0 km/ hr at the two Poles.

In 1835, GD Coriolis, a French mathematician first proved that the rotation of the Earth is responsible for the generation of a centrifugal force which is known as the Coriolis force.

WBBSE Class 9 Geography And Environment Chapter 2 Movements Of The Earth Notes

WBBSE Class 9 Movements of the Earth Notes

Under the influence of centrifugal force due to the rotation of the Earth, the ocean currents and planetary winds deflect from their direction in both hemispheres, which is known as Ferrel’s law.

The circumference of the Earth’s orbit is 960 million km.

The axis of the Earth is an imaginary line. that joins the North and the South Poles and passes through the center of the Earth.

The Earth’s axis remains permanently tilted at an angle of 66 to the Earth’s orbital plane.

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Movements Of The Earth Class 9 WBBSE Geography Summary

The phenomenon of equal lengths of day and night all over the Earth is called equinox. The days and nights are of equal duration everywhere on Earth on 21 March and 23 September. These days are called vernal equinox in the northern hemisphere and autumnal equinox in the southern hemisphere respectively.

On 21 June, sunrays fall vertically over the Tropic of Cancer, and the day is called the summer solstice.

On 22 December, sunrays fall vertically over the Tropic of Capricorn, and the day is called the winter solstice.

The average velocity of the Earth’s revolution is 30km/sec.

Key Terms Related to Earth’s Movements for Class 9

Aurora in the north polar region and the south polar region is known as Aurora Borealis and Aurora Australis respectively.

The Earth is farthest from the Sun (approximately 152 million km) on July 4. This phenomenon is called Aphelion.

The Earth is closest to the Sun (approximately 147 million km) on January 3. This phenomenon is called Perihelion. Movements of the Earth

The apparent movements of the Sun are of two types, namely Apparent diurnal movement and 2 Apparent annual movements of the Sun.

Every day, we get to see the Sun rises in the east and set in the west. This is called the apparent diurnal movement of the Sun.

All through the year, it seems that the Sun moves between the Tropic of Cancer and the Tropic of Capricorn. This is known as the apparent annual movement of the Sun.

The apparent path of the Sun throughout the year is known as the ecliptic.

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