Motion of the Earth

Motion of the Earth notes || Class 6 Chapter 3 Geography ||

Chapter – 3

MOTIONS OF THE EARTH

Important Points

1.      Rotation – It is the movement of the earth on its axis in about 24 hours.

2.      Revolution – The movement of the earth around the sun in a fixed path or orbit in a period of one year.

3.      Seasons – divisions of the year marked by different weather (मौसम) patterns

4.      Solstices – position of the earth in its orbit on 21 June and 22 December

5.      Equinoxes – position of the earth in its orbit on 21 March and 23 September

6.      Aphelion – position of the earth on 4 July of every year when the distance between earth and the sun is maximum (151 million km or 15.1 crore km)

7.      Perihelion - position of the earth on 4 January every year when the distance between earth and the sun is minimum (146 million km or 14.6 crore km)

Rotation of the Earth

1.      Rotation is the movement of the earth on its own axis while revolution is the movement of the earth around the sun in a fixed path called its orbit.

2.      Earth’s axis is inclined from the vertical line at an angle of 23.5⁰ & makes an angle 66.5⁰ with its orbital plane.

3.      The earth is always remains tilted to one side while moving around the sun & this tilt (झुकाव) is called inclination of the earth’s axis.

4.      The earth takes about 24 hours (rotates at 1670 km/hr in 23 hr 56 min 4 sec) to complete one rotation around its axis.

5.      The period of rotation is known as the earth day.

The Circle of Illumination

1.      The earth has spherical shape & receives light from the sun.

2.      So that only half portion gets light from the sun at a time.

3.      The portion facing the sun experiences day while the other half away from the sun experiences night.

4.      The circle that divides the day from night on the globe is called the circle of illumination (प्रकाशन).

Revolution of the earth

1.      The motion of the earth (29.85 km/s) around the sun in its orbit is called revolution.

2.      This orbit generally in elliptical shape

3.      It takes 365 days and 6 hours (5hrs 48min and 56sec) to revolve around the sun.

4.      A year is consisted of 365 days is called ordinary year

5.      The remaining 6 hours is adjusted as one extra day after every four years which is added to the month of February.

6.      Therefore, every fourth year, February has 29 days & that year has 366 days.

7.      This year is called a Leap year.

8.      Earth completes one revolution in one year & divided into 4 seasons – spring (वसन्त), summer, Winter & Autumn (पतझड़)

Movement of Earth around the Sun

1.      In the given picture, 4 selected days i.e., 21 March (Position 1), 21 June (Position 2), 23 Sept (Position 3), and 22 Dec (Position 4).

2.      The day on which the sun shines vertically overhead at the tropic of cancer or tropic of Capricorn and the duration of the day is longest in the hemisphere, is called solstice.

3.      The Position 2 & 4 of the earth is Solstice.

4.      The day on which the sun shines vertically overhead at the equator & the duration of the days & nights are equal, is called equinox.

5.      The Position 1 & 3 of the earth is equinox.

Summer Solstice – 21 June

1. Northern hemisphere experiences the longest day & shortest night.
2. At this position, the North Pole is inclined (झुकना) towards the sun.
3. The places beyond (के आगे) the Arctic Circle experience continuous daylight for about six months.
4. The position of the Earth on 21 June is known as the summer solstice because it is the summer in the Northern hemisphere.
5. Sun rays fall vertically on the Tropic of the cancer. Therefore, places in the northern hemisphere experiences summer season.
6. During this time, the conditions are just the reverse in Southern hemisphere. It is turned away from the Sun. Therefore, it receives slanting (तिरछा) rays.
7. The duration of the daylight is short & it is winter season.

Winter Solstice – 22 December

1. Places in the Southern hemisphere experiences the longest day & shortest night.
2. The position of the Earth on 22 Dec is known as the winter solstice because it is the winter in the Northern hemisphere.
3. South Pole is inclined towards the sun.
4. Sun rays fall vertically on the Tropic of the Capricorn. Therefore, it is summer season in the southern hemisphere.
5. During this time, the conditions are just the reverse in Northern hemisphere. It is turned away from the Sun. it receives slanting rays.
6. Days are short & nights are long.
7. Hence, it is winter season in the Northern hemisphere.

Spring & Autumnal Equinoxes – 21 March & 23 September

1. Position of the Earth on 21 March known as Spring (वसन्त) Equinox
2. Sun shines vertically over the Equator.
3. At this position, neither of the poles is tilted towards the sun.
4. They lie at an equal distance from the sun.
5. It results in equal days & nights at all places on the Earth.
6. Similarly, on 23 Sept known as Autumnal Equinox, the Sun shines vertically over the Equator.

Aphelion and Perihelion

1. Perihelion – Peri means near & helios means the Sun.
2. Aphelion – Ap means away from and helios means the Sun.

Dawn and Twilight/Dusk

1. Dawn – The part of the day just before the sunrise in the East.
2. Twilight – The part of the day when the sun sets in the West & there is still some light