Motions of the Earth

Quick Revision Notes: Class 6 Social Science (Geography)

Chapter: Motions of the Earth (पृथ्वी की गतियाँ)

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1. Introduction to Earth's Motions (पृथ्वी की गतियाँ)

The Earth has two types of motions on its axis and in space. These movements affect day and night, and the change of seasons.

• Axis (अक्ष): An imaginary line making an angle of 66.5° with its orbital plane.
• Orbital Plane (कक्षीय समतल): The plane formed by the orbit of the Earth around the Sun.

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2. Rotation (घूर्णन / परिभ्रमण)

• Definition: The movement of the Earth on its own axis from West to East.
• Time Taken: Takes about 24 hours (one complete day) to complete one rotation.
• Key Effect: Causes Day and Night (दिन और रात).
• Circle of Illumination (प्रदीप्ति वृत्त): The imaginary circle that divides the day from night on the globe.

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3. Revolution (परिक्रमण)

• Definition: The movement of the Earth around the Sun in a fixed path or orbit.
• Shape of Orbit: Elliptical (दीर्घवृत्ताकार).
• Time Taken: Takes 365 ¼ days (one year) to complete one revolution.
• Leap Year (लीप वर्ष):
  • Every year, 6 hours (¼ day) are saved and added to make one day (24 hours) over a span of four years.
  • This extra day is added to the month of February.
  • A leap year has 366 days.

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4. Change of Seasons (ऋतुओं में परिवर्तन)

Seasons change due to the change in the position of the Earth around the Sun and the tilt of the Earth's axis.

A. Summer Solstice (उत्तर अयनंत) – June 21

• Position: The Northern Hemisphere is tilted towards the Sun.
• Effect:
  • Longest day and shortest night in the Northern Hemisphere.
  • Summer season in the Northern Hemisphere and Winter season in the Southern Hemisphere.

B. Winter Solstice (दक्षिण अयनंत) – December 22

• Position: The Southern Hemisphere is tilted towards the Sun.
• Effect:
  • Longest day and shortest night in the Southern Hemisphere.
  • Winter season in the Northern Hemisphere and Summer season in the Southern Hemisphere.

C. Equinox (विषुव) – March 21 and September 23

• Position: Direct rays of the Sun fall on the equator. Neither of the poles is tilted towards the Sun.
• Effect:
  • Equal days and equal nights all over the world.
  • March 21: Spring Equinox (वसन्त ऋतु) in the Northern Hemisphere and Autumn in the South.
  • September 23: Autumn Equinox (शरद ऋतु) in the Northern Hemisphere and Spring in the South.

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Quick Facts for MP Board Exam (महत्वपूर्ण बिंदु)

1. Rotation = Daily motion (Axis par ghumna) $\rightarrow$ Day and Night.
2. Revolution = Annual motion (Suraj ke charo taraf chakkar lagana) $\rightarrow$ Change of Seasons.
3. The Earth's orbital plane angle = 66.5° tilt from the orbital plane, or axis makes an angle of 23.5° from the vertical.
4. Australia experiences Christmas in summer season (December).