Motions Of The Earth

Motions of the Earth

• The earth has two types of motions

→ Rotation

→ Revolution

• Rotation is the movement of the earth on its axis.
• The movement of the earth around the sun in a fixed path or orbit is called Revolution.
• Orbital plane: The axis of the earth which is an imaginary line, makes an angle of 66½° with its orbital plane. The plane formed by the orbit is known as the orbital plane.
• Tilt of Axis: Earth’s axis is tilted at an angle of 66.5° on its orbital plane. On the other hand, the earth’s axis is tilted at 23.5° on the line which is perpendicular to its orbital plane.
• The circle that divides the day from night on the globe is called the circle of illumination.
• The earth takes about 24 hours to complete one rotation around its axis.

→ The period of rotation is known as the earth day meaning daily motion of the earth.

→ The time taken by the earth to complete one revolution is called one year. One year has 365 and ¼ days (365 days and 6 hours).

What Would Happen if the Earth Did Not Rotate?

• If there had been no rotation of the earth; one half of the earth would have been constantly in daylight and another half would have been constantly in dark.

→ The portion under sunlight would have been too hot.

→ The portion in dark would have been freezing cold.

→ Such extremes of temperature could have made it impossible for life to thrive on our planet.

Perihelion and Aphelion

• Perihelion: The point at which a planet is nearest to the sun.
• Aphelion: The point at which a planet is farthest from the sun.

Equinox

• On 21st March and 23rd September, direct rays of the sun fall on the equator.
• At this position, neither of the poles is tilted towards the sun, so the whole earth experiences equal days and equal nights.

→ This is called an equinox.

Summer Solstice

• On 21st June, the Northern Hemisphere is tilted towards the sun. The rays of the sun fall directly on the Tropic of Cancer.
• These areas receive more heat, while the areas near the poles receive less heat as the rays of the sun are slanting.
• The North Pole is inclined towards the sun, and the places beyond the Arctic Circle experience continuous daylight for about six months.
• Since a large portion of the Northern Hemisphere is getting light, it is summer in the regions north of the equator.

→ The longest day and the shortest night occur on 21st June.

→ At this time in the Southern Hemisphere, all conditions are reversed – it is winter, and the nights are longer than the days.

Winter Solstice

• On 22nd December, the Tropic of Capricorn receives direct rays of the sun as the South Pole tilts towards it.
• As the sun’s rays fall vertically at 23½° S, a larger portion of the Southern Hemisphere gets light.
• Therefore, it is summer in the Southern Hemisphere with longer days and shorter nights.

→ The reverse happens in the Northern Hemisphere.

MCQs

1. The sun rays are vertical over the ________ during ______

(a) Tropic of Capricorn, equinox

(b) Tropic of cancer, winter solstice

(c) Tropic of Capricorn, summer solstice

(d) Tropic of cancer, summer solstice

► (d) Tropic of cancer, summer solstice

2. A mean solar day is

(a) The average time taken for Earth to rotate on its axis: 24 hours

(b) The time taken for the Earth to go once around the Sun

(c) A day when the sun emits a lot of dangerous particles

(d) The time taken for the Earth to go once around the Sun

► (a) The average time taken for Earth to rotate on its axis: 24 hours

3. How many Solstices are there in every year

(a) 2

(b) 3

(c) 5

(d) 4

► (a) 2

4. The axis of the earth which is an imaginary line, makes an angle of 66º with its

(a) Rotational plane

(b) Orbital plane

(c) Revolution Plane

(d) Southern plane

► (b) Orbital plane

5. The earth takes _____ to complete one revolution

(a) 365 days and 9 hours

(b) 365 days and 8 hours

(c) 365 days and 7 hours

(d) 365 days and 6 hours

► (d) 365 days and 6 hours

6. Seasons change due to the change in the position of the earth around the

(a) Moon

(b) Mars

(c) Saturn

(d) Sun

► (d) Sun

7. Earth's movement around sun is called

(a) Rotation

(b) Revolution

(c) Solstice

(d) Equinox

► (b) Revolution

8. Days are shorter during

(a) Rainy

(b) Winter

(c) Summer

(d) Autumn

► (b) Winter

9. In leap year, the month of February has

(a) 31 days

(b) 29 days

(c) 30 days

(d) 28 days

► (b) 29 days

10. It is the position of the earth when the Northern Hemisphere has the longest day and the shortest night

(a) Winter Solstice

(b) Summer Solstice

(c) Day Solstice

(d) Night Solstice

► (b) Summer Solstice

11. Earth receive light from the

(a) Moon

(b) Mars

(c) Sun

(d) Venus

► (c) Sun

12. Two motions of the earth are

(a) Rotation and Revolution

(b) Rotavation and Revolution

(c) Rotaional and Revotation

(d) Rotation and Revotation

► (a) Rotation and Revolution

13. How much time does the earth take time to complete its rotation?

(a) 22

(b) 23

(c) 24

(d) 20

► (c) 24

14. Earth moves on axis

(a) Solstice

(b) Rotation

(c) Revolution

(d) Season

► (b) Rotation

15. In perihelion, Helios means

(a) Hydrogen

(b) Light

(c) Hemisphere

(d) Sun

► (d) Sun

16. Leap day is always added to the month of

(a) February

(b) March

(c) January

(d) December

► (a) February

17. The sun's rays fall vertically on the ______ on 21st. June

(a) Arctic Circle

(b) Tropic of Cancer

(c) Tropic of Capricorn

(d) Antarctic Circle

► (b) Tropic of Cancer

18. Poles experience about

(a) Six months of day and three months of night

(b) Six months of day and two months of night

(c) Six months of day and six months of night

(d) Six months of day and four months of night

► (c) Six months of day and six months of night