Motion of the Earth PDF

## 5. Motions of the Earth - **Shape of the Earth** - The Earth is spherical in shape, but not a perfect sphere. - Its exact shape can be defined by the word "geoid", which means "Earth-like". - The Earth is slightly flattened at the poles and bulging at the centre. - The globe is a mode...

## 5. Motions of the Earth - **Shape of the Earth** - The Earth is spherical in shape, but not a perfect sphere. - Its exact shape can be defined by the word "geoid", which means "Earth-like". - The Earth is slightly flattened at the poles and bulging at the centre. - The globe is a model of the Earth. - It is also shaped like the Earth and has an axis on which it rotates. - Like the Earth, it also has two ends, the North Pole and the South Pole. - With the help of a globe, we can easily understand the movements of the Earth. - There is an imaginary line that runs around the middle of the Earth, dividing it into two equal halves. - This line is called the equator. - The Equator splits the Earth into two halves - the Northern hemisphere and the Southern hemisphere. - **Rotation of the Earth** - The movement of the Earth on its axis is called rotation. - The axis is an imaginary line passing vertically through the center of the Earth, connecting the North Pole and the South Pole. - The Earth's axis is tilted at an angle of 23 ½°. - The Earth rotates on this imaginary line from West to East. - This is the reason that we see the sun rising in the East and setting in the West. - The Earth completes one rotation on its axis in approximately 24 hours or one day. - Rotation also causes winds and movements in the oceans. - **How are days and nights caused?** - The rotation of the Earth causes days and nights. - As the Earth rotates, the part of the Earth facing the Sun receives light and thus has day, while the other half of the Earth does not receive any light and has night. - As the Earth keeps rotating, the darker part turns to the Sun and experiences day. - Thus, all parts of the Earth get day and night once in 24 hours. - **Curvature of the Earth** - The intensity of the Sun's rays is high, especially when the Sun is shining directly overhead. - But in the evening, the intensity of the Sun's rays reduces as the rays are slanting. - Just as there is variation in the intensity of heat during the day, you will find variation in temperatures at different places on the Earth. - This is due to the curved surface of the Earth. - Places lying closer to the Equator are hotter than the places closer to the poles, because the Equator receives direct sunlight and the intensity of heat is maximum there. - As we move away from the Equator, the curvature of the Earth increases. - The Sun's rays fall on the Earth at a slanting angle and these parts of the Earth are farther away from the Sun. - Therefore, places lying farther away from the Equator are colder. - **Revolution of the Earth** - The Earth not only rotates on its axis but also moves around the Sun. - The movement of the Earth around the Sun is called revolution. - Like all planets in the Solar System, the Earth also revolves around the Sun on a fixed path called the orbit. - The Earth completes one revolution in 365 ½ days or one year. - The Earth takes 365 days and 6 hours to go around the Sun. - But our calendar year consists of 365 days only. - The extra 6 hours are added after every four years when they become 24 hours, and an extra day is added to the year in the month of February. - This year which has 366 days is called the leap year. - Revolution of the Earth around the Sun causes seasons. - There are mainly four seasons - summer, autumn, winter and spring. - **How are seasons caused?** - Seasons are caused mainly because of two factors - - the revolution of the Earth - the tilt of the Earth's axis - If you look at diagram 1, you will see that the North Pole leans towards the Sun. - Therefore, the Northern Hemisphere receives the direct rays of the Sun and has summers, while the Southern Hemisphere receives slanting rays and has winters.) - In Diagram 2, the South Pole is inclined towards the Sun. - Now, the Southern Hemisphere receives vertical and direct rays of the Sun and experiences the hot summer season. - At the same time, the North Pole is tilted away from the Sun. - Here, the Sun's rays are slanting and spread over a greater surface area. - Thus, the Northern Hemisphere experiences cold winters. - **Cycle of Seasons** - Seasons repeat almost at the same time of the year because the Earth completes one revolution around the Sun in one year. - So, the same part of the Earth faces the Sun at the same time every year. - This forms a cycle of seasons. - Seasons are caused in the following pattern: - February to April: Spring in the Northern Hemisphere, autumn in the Southern Hemisphere - May to July: Summer in the Northern Hemisphere, winter in the Southern Hemisphere - August to October: Autumn in the Northern Hemisphere, spring in the Southern Hemisphere - November to January: Winter in the Northern Hemisphere, summer in the Southern Hemisphere