Motions of the Earth: An Overview

The Earth undergoes several motions that govern its position and orientation in space. These motions of the Earth include its rotation on its axis, which causes day and night, its revolution around the Sun, which gives rise to seasons, and its axial tilt, which results in variations in climate and daylight throughout the year. These Earthly motions play a crucial role in shaping the planet’s geography and climatic patterns.

The earth has two types of motions of the Earth, namely Rotation and Revolution.

Earth’s Rotation: The spinning motions of the Earth

• It is the motions of the earth on its axis. 
• This is the daily motions of the earth. 
• Duration of Rotation: The earth takes about 24 hours to complete one rotation around its axis. The period of rotation is known as the earth day (Refer Figure 2.13). 
• If the earth did not rotate: The portion of the earth facing the sun would always experience day, thus bringing continuous warmth to the region and the other half would remain in darkness and be freezing cold all the time. 
• Significance of Rotation: Life would not have been possible in such extreme conditions. 

Earth’s Revolution: Understanding orbital motions of the Earth around the sun

• Earth’s Revolution: The motions of the earth around the sun in a fixed path or elliptical orbit is called Revolution.
• Duration of Revolution: The Earth takes 365¼ days (one year) to revolve around the sun. Throughout its orbit, the earth is inclined in the same direction.
  • We consider a year as consisting of 365 days only and ignore six hours for the sake of convenience. 
• Leap Year Adjustment: Six hours saved every year are added to make one day (24 hours) over a span of four years and this surplus day is added to the month of February. 
  • Thus every 4th year, February has 29 days instead of 28 days and such a year with 366 days is called a Leap Year. 
• Seasonal Changes: A year is usually divided into summer, winter, spring and autumn seasons and these seasons change due to the change in the position of the earth around the sun (Refer Figure 2.14). 

 Summer Solstice: Earth’s Northern Heat and Southern Chil

• On 21st June, the position of the earth is called the Summer Solstice as the Northern Hemisphere is tilted towards the sun and the rays of the sun fall directly on the Tropic of Cancer. 
  • As a result, these areas receive more heat. 
  • The areas near the poles receive less heat as the rays of the sun are slanting. 
• Temperature Variation: The North Pole is inclined towards the sun and the places beyond the Arctic Circle experience continuous daylight for about six months. 
• Summer in the Northern Hemisphere: Since a large portion of the Northern Hemisphere is getting light from the sun, it is summer in the regions north of the equator. 
  • The longest day and the shortest night at these places occur on 21st June. 
• Winter in the Southern Hemisphere: At this time in the Southern Hemisphere it is winter season there. The nights are longer than the days (Refer Figure 2.14). 

Winter Solstice: Seasonal Shifts in Earth’s Hemispheres

• On 22nd December, the position of the earth is called the Winter Solstice as the Tropic of Capricorn receives direct rays of the sun as the South Pole tilts towards it. 
• Sun’s Rays at Tropic of Capricorn: As the sun’s rays fall vertically at the Tropic of Capricorn (23 1⁄2° S), a larger portion of the Southern Hemisphere gets light. 
• Northern and Southern Hemispheric Contrast: it is summer in the Southern Hemisphere with longer days and shorter nights. 
  • The reverse happens in the Northern Hemisphere . 

Equinox: Balancing Days and Nights in Earth’s Seasons

• On 21st March and September 23rd, neither of the poles is tilted towards the sun and direct rays of the sun fall on the equator. 
  • So, the whole earth experiences equal days and equal nights. 
  • This is called an equinox. 
• On 23rd September, it is autumn season in the Northern Hemisphere and spring season in the Southern Hemisphere. 
• On 21st March, it is spring in the Northern Hemisphere and autumn in the Southern Hemisphere . 

Conclusion

The origin and evolution of the earth is a complex and ongoing process that has occurred over billions of years. In this process of evolution life appeared on earth. Astronomers and scientists started exploring the universe and we have come very far. But we still haven’t fully figured out the truth of the Universe.

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