# Motions of the Earth CBSE Class 6 GEOGRAPHY Chapter 3 Notes

## Types of Motion of the Earth

Earth has two types of motion:

1. Rotation It is the movement of the Earth on its axis.
2. Revolution It is the movement of the Earth around the sun in an orbit (fixed path).

## Orbital Plane and Circle of Illumination

• The plane formed by the orbit is known as the orbital plane.
• The axis of the Earth (an imaginary line) makes an angle of 66% with its orbital plane.
• The spherical shape of the Earth allows only half of the sunlight to come at a time.
• The portion facing the sun experiences day while the other half away from the sun experiences night.
• The circle that divides the day from night on the Earth is called the circle of illumination.
• The Earth takes about 24 hrs to complete one rotation around its axis.
• The period of rotation is known as Earthday.
• This is the daily motion of the Earth.

## Revolution of the Earth

• The movement of the Earth on its axis around the sun is called revolution (second type of motion of the Earth).
• It takes 365 days (one year) and 6 hours to revolve once around the sun.
• We ignore six hours for the sake of convenience and consider a year consisting of 365 days.
• Saved six hours are added to make one day (24 hours) over span of four years.
• This surplus day is added to the month of February and in every fourth year, February is of 29 days in spite of 28 days.
• The year with 366 days is called a leap year.
• The Earth moves around the sun being inclined in the same direction throughout the year, in an elliptical orbit.

## Seasons

• Seasons change due to changes 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.
• On 21st June, the Northern hemisphere is tilted towards the sun.
• These areas receive more heat because sun rays fall directly on the tropic of Cancer.
• 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 Northern part of the equator.

### Summer Solstice

• In summer season, the regions North of the equator experience the longest day and shortest night on 21st June.
• The rays of the sun fall directly on the tropic of Cancer.
• All these conditions are opposite in Southern hemisphere and it is winter there.
• The nights are longer than the days.
• This position of the sun is called the Summer Solstice.

### Winter Solstice

• The tropic of Capricorn receives direct rays due to tilting of South Pole towards sun on 22nd December.
• The vertically falling sun rays at the tropic of Capricorn 23% provide heat to a larger portion of it.
• Therefore, it is summer in Southern hemisphere.
• The days are longer with shorter nights in Southern hemisphere in summer while the conditions are reversed in the Northern hemisphere. This position of the Earth is called the Winter Solstice.

#### fact

• Christmas in Australia and New Zealand is celebrated in summer.
• The Northern hemisphere experiences autumn season while Southern hemisphere spring season on 23rd September.
• On 21st March, it is spring in Northern hemisphere and autumn in Southern hemisphere.

## Equinox

• The direct rays of the sun fall on the equator on 21st March and 23rd September.
• The whole Earth experiences equal days and equal nights because neither of the poles is tilted towards the sun. This is called an equinox.
• Thus, the days and nights and changes in seasons on Earth are experienced because of rotation and revolution of the Earth respectively.

1. Orbital Plane The plane formed by the orbit is known as the orbital plane.
2. Circle of Illumination The circle that divides the day from night on the Earth is called circle of illumination.
3. Earth Day The period of rotation (daily motion of the Earth) is known as the Earth day.
4. Leap Year The year with 366 days is called a leap year.
5. Elliptical Orbit The Earth moves around the sun in an elliptical orbit
6. Summer Solstice The days are longer with shorter nights in the Northern hemisphere in summer while the conditions are reversed in the Southern hemisphere. This position of the Earth is called the Summer Solstice.