The Earth in the Universe

After completion of this lesson, student must be able to:

  • Describe diurnal and annual motion of the earth.
  • Explain the phases of the moon.
  • Determine the relation of the position of the moon, the earth and the sun.
  • Explain with a diagram, umbra and penumbra of a shadow.
  • Explain lunar and solar eclipses with reason and diagram.


Introduction: The Earth in the Universe

The Milky Way galaxy is a medium sized galaxy, which consists of about 150 billion of stars. Pluto was removed from the planet as it was not massive (large) enough to become a planet and it crossed the path of Neptune. This note gives us more information about the universe and solar system.

Phases of Moon

When we observe the sky daily for some days, we find that the moon changes its shape every day. It is called phases of the moon. This note provides us the information about different phases of moon.


The moon completes one revolution around the earth in about 27.33 days (27 days, 73 hour, 43 minutes and 11.5 second). This period is called sidereal month. The time taken by the moon to come from m1 to m3 condition is called synodic month or a lunar month. Thus, the duration between two consecutive new moons is synodic month. This note provide us the information about sidereal and synodic month along with eclipse and its types.

The Earth

Earth is also known as the green planet. It is the third planet from the sun at a distance of about 150 million kilometers. This note provides information about the earth, diurnal and annual motion of earth, effect of rotation and revolution of earth.