MOTIONS OF THE EARTH

In 1687, Sir Isaac Newton propounded that the shape of the earth is the Oblate Sphere. A sphere that is at the poles and bulges out around the centre. The bulge is due to the centrifugal force. The modern-day scholars consider the shape of the earth as Geoid. The earth is the third planet of the solar system and exhibits two types of motion- the Rotational Motion and the Revolution Motion.

ROTATION OR DAILY MOTIONS OF THE EARTH– The movement of earth about its axis is called the rotation of the earth. The earth rotates on its imaginary axis in West to East direction once in 23 hours, 56 minutes and 41 seconds. thus the sun, moon along with stars rise in the East and sets in the West. The earth rotates on its imaginary axis. The axis is defined as an imaginary line that runs from north to south pole and passes through the centre of the earth. The axis of the earth is inclined at an angle of 66 1/2° to the plane of the earth’s orbit. The axis of the always point towards the pole star. As we go north and south of the equator the rotation decreases. At 45° latitude, the earth spins at a speed of 1120 KM/HOUR. The speed at the equator is 1670 Km/ HOUR.

IMPORTANCE OF THE ROTATION

The occurrence of day and night.
Deflection of winds and ocean currents.
The movement of the Sun, Moon and the Stars.
The position of a place can be fixed.
The shape of the earth i.e Oblate Sphere.

SOLAR DAY– The duration of a solar day is of 24 hours. In a solar day, the position of the sun is stationary and the earth revolves around the sun. this phenomenon is called as solar day and it is calculated in terms of the day.

SIDEREAL DAY– The duration between the passage of a particular star over a meridian twice is called a sidereal day.

REVOLUTION MOTIONS OF THE EARTH– The revolution is an annual motion of the earth. While rotating on its axis earth revolves around the sun in an elliptical path called the orbit. It takes 365 days 6 hours 9 minutes and 9.54 seconds to complete its one revolution. During the revolution, the average orbital velocity is 29.8 KM/HOUR. This is also known as the solar year.

IMPORTANCE OF THE REVOLUTION

The season on earth occurs due to revolutions.
Variations in the length of day and night.
Changing altitude of the mid-day sun.

PERIHELION– On 3rd January, the earth is at the minimum distance from the sun.

APHELION– On 4th July, the earth is at the maximum distance from the sun.

SOLSTICE AND ITS TYPES– Two times of the year at which the sun reaches its highest point or lowest point in the sky at noon and marked as longest and the shortest days. The solstice is of two types- the Summer Solstice and the Winter Solstice.

SUMMER SOLSTICE– In summer solstice, the sun is perpendicular over the Tropic Of Cancer i.e the north pole is tilted towards the sun. It occurs on 21st June, days are long and nights are short.

WINTER SOLSTICE– In winter solstice, the sun is perpendicular over the Tropic Of Capricorn i.e the south pole is tilted towards the sun. It occurs on 22nd December, days are short and nights are long.

EQUINOX AND ITS TYPES– The sun is perpendicular over the equator. The duration of the length of day and night is equal. It is termed as the equinox. This phenomenon occurs twice in a year-