Motion of the Earth

Rotation

• • The Earth spins on its axis from west to east.
  • It takes 24 hours to complete one full rotation.
  • Causes day and night.
  • The speed of rotation is fastest at the equator (~1,600 km/h) and decreases towards the poles.

Revolution

• • The Earth moves around the Sun in an elliptical orbit.
  • It takes 365¼ days (~one year) to complete one revolution.
  • Causes seasons due to the tilt of the Earth’s axis.

Orbital Plane

• • • The imaginary plane in which the Earth orbits around the Sun.
    • The Earth’s axis is tilted at 66.5° to the orbital plane.
    • This tilt is responsible for seasonal changes.

  

Circle of Illumination

• • The imaginary line separating the day and night sides of the Earth.
  • Due to the Earth’s spherical shape, only one-half of the planet receives sunlight at any given time.
  • The tilt of the Earth affects the length of daylight hours.

Earth Day

• • The time taken by Earth to complete one full rotation.
  • It is approximately 24 hours (23 hours, 56 minutes, and 4 seconds).
  • Divided into daytime and nighttime depending on location.

Leap Year

• • The Earth takes 365¼ days to revolve around the Sun.
  • To adjust for the extra ¼ day, an extra day (February 29) is added every four years.
  • The last leap year was 2020, and the next one is 2024.

Elliptical Orbit

• • The Earth’s orbit around the Sun is not a perfect circle but an ellipse.
  • Due to this, the distance between the Earth and the Sun varies throughout the year.
  • Closest to Sun (Perihelion): January 3 (~147 million km).
  • Farthest from Sun (Aphelion): July 4 (~152 million km).

Summer Solstice

• • Occurs on June 21.
  • Sun shines directly over the Tropic of Cancer (23.5°N).
  • Northern Hemisphere: Longest day & shortest night (Summer).
  • Southern Hemisphere: Shortest day & longest night (Winter).

Winter Solstice

• • Occurs on December 22.
  • Sun shines directly over the Tropic of Capricorn (23.5°S).
  • Northern Hemisphere: Shortest day & longest night (Winter).
  • Southern Hemisphere: Longest day & shortest night (Summer).

Equinox

• Occurs on March 21 (Spring Equinox) and September 23 (Autumn Equinox).
• The Sun is directly overhead at the Equator.
• Day and night are of equal length worldwide.
• Marks the transition between seasons.