Student Portal


Investigation 2 – PreLab









Astrophysicists apply the laws of physics and chemistry to explain the birth, life, and death of stars, planets, galaxies, nebulae, and other objects in the universe.


This Investigation is designed to help you to answer the following Focus Question:

  • Based on your model, why do you think we observe different phases of the Moon from the Earth? 

Note: This question is located in your SDR at the beginning and end of the Investigation.



As a class, read the Background(s) in the Investigation. When finished, discuss the following concepts as a class:

  • Earth rotates, or spins, on a tilted axis.
  • The planet Earth has one object in a constant orbit around it, which is called the Moon.
  • The Moon revolves around the Earth, held in place by the Earth’s field of gravity.
  • While the Moon revolves around the Earth, it revolves around the Sun with the Earth. The result is that anyone who views the Moon from the Earth sees different portions of the Moon that are illuminated by the light from the Sun. These visible portions of the Moon are what is termed the phases of the Moon.


These terms should be used, as appropriate, by teachers and students during everyday classroom discourse.

  • revolution

Note: The definition of this term can be found on the Introduction page to the CELL.

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.


  • Briefly review how the motion of the Earth produces changes in the light that reaches Earth both in terms of day and night and the seasons.
  • Discuss how the differences in the light that reaches the Earth changes the appearance of our environment. 
  • Think of another celestial body whose appearance changes during the month. If necessary, review the phases of the moon.
    • Does the Moon always appears the same from one night to the next?
    • The different appearances of the Moon are called phases.
  • Form a hypothesis of why we on Earth observe different phases of the moon.
    • Might it relate to the changes in the motion of the Earth or Moon? Briefly discuss various ideas.
  • Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful in the lab.
  • After the video, divide into lab groups to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video.


You should review the Investigation and video in preparation for the Lab.