Lesson Plan - Phases of the Moon

Suggestions for instructors

The most common misconception students have with understanding how the phases of the Moon occur is that they think that the phases of the Moon are caused by the shadow of the Earth falling on the Moon. This will likely be the belief held by the majority of your students, and it is important to show that this preconception is incorrect before showing the correct answer.

An alternative to using circular cutouts to show the difference in an eclipse and the phases of the moon is to use a projector and a round object to cast a shadow. If you are using a projector in your classroom, consider using a small globe placed between the projector and the board such that it casts a circular shadow. Trace the outline of the shadow on the board, and show that as you move the Earth from side to side, that the shape created is not the same shape as the phases of the moon.

A common exercise used in helping students overcome misconceptions regarding phases of the Moon is to have them create a model of the phases of the Moon by giving students pictures of the phases of the Moon, a picture of the Earth, and a picture of the Sun, and then having each student take a picture, and stand in the correct place to make the phases of the Moon match. For instance, the student with the picture of the Sun would stand on the opposite side of the room form the rest of the class, and the students with pictures of the phases of the Moon would stand in a circle around the student with the picture of the Sun.

Standards

The exploration meets the following National Standards:  Science Content Standards: 9-12

• CONTENT STANDARD A:
• Abilities necessary to do scientific inquiry
• Understandings about scientific inquiry
• Fundamental abilities and concepts that underlie this standard include:
  • Use technology and mathematics to improve investigations and communications.
  • Formulate and revise scientific explanations and models using logic and evidence.
  • Recognize and analyze alternative explanations and models.
  • Communicate and defend a scientific argument.
• CONTENT STANDARD B:
• Physical Science Standards
  • Structure and properties of matter
  • interactions of energy and matter
• Earth and Space Science Standards
  • Origin and evolution of the universe
  • Origin and evolution of the earth system
• History of Science Standards
  • Nature of scientific knowledge

Solutions

1. Can you identify a waxing crescent moon in the animation?
   Waxing refers to increasing in size, the crescent moon appears as a little more than a sliver. This occurs just after the new moon (moon entirely dark) in the lunary cycle.
2. Can you identify a waning gibbous moon in the animation?
   The waning gibbous (nearly full) moon appears just after the full moon in the lunar cycle.
3. Describe what you think causes the phases of the moon. Discuss this with your classmates.
   The cause of the phases of the moon is a common misconception. This question should be asked before having the students attempt any models or exercises, so that they can return to it later. At this time, the actual answer is not as important as getting the students to describe what they think happens. Most will likely give the common misconception that the phases of the moon occur due to the shadow of the Earth falling on the moon.
4. Using two overlapping circles, one dark and one light, try to determine what the moon would look like as the shadow of the Earth passed across it. Draw pictures of the result of this shadow.
   Students should see that the shadow of the Earth on the Moon will always create a concave cutout, either during the gibbous or crescent phases.
5. Compare your pictures of the shadow crossing the moon to the animation of the phases of the moon. Do you think that the phases of the moon are caused by the shadow of the Earth? Why or why not?
   Students should see that the data of the phases of the moon show a convex curve on the gibbous moon, and a concave curve on the crescent moon, in conflict with their model of the shadow of the Earth on the moon.
6. Using the lunar phase viewer applet, place the Earth, Moon, and Sun in a position such that an angle with the Earth at its vertex and the Moon and Sun at each end is a 90 degree angle. What would you expect the Moon to look like from Earth?
   Students should see that 1/4 of the way through the lunary cycle, if what we are seeing is the light from the sun reflected off of the moon, that we would see a half moon.
7. What would the moon look like if the angle were greater?
   Crescent
8. What would the moon look like if the angle were smaller?
   Gibbous
9. What is it called when the shadow of the Earth falls on the Moon?
   A lunar eclipse
10. What is it called when the Moon passes between the Earth and the Sun?
    A solar eclipse