Phases of the Moon
This material is replicated on a number of sites as part of the SERC Pedagogic Service Project
- Understand why the moon changes phases
- Recognize the importance of an observer's perspective
- Get personally involved in the lesson
Context for Use
Each student or group of student gets a sphere, tennis-ball size or larger, to represent the moon.
Ask the students, in groups of four, to work out an explanation of the phases of the moon that they can write down (legibly) on an index card that they then hand in (for a participation grade, the information is not expected to be correct). Students then pick up the spheres, and the instructor turns out all of the overhead lights (make sure windows are covered by curtains or blinds) and turns on one light source, taking the role of the Sun (a powerful one if teaching in a lecture hall).
Have each student with a "moon" hold it up in front of them as they face the instructor. Ask them what phase the moon is in, assuming that they are the Earth ("new moon"; make sure they agree on this). Then ask them (or students without "moons", if there are any) "How much of the moon is lit?" (one-half, make sure everyone can see this, if need be by looking over their shoulders at the "moons" behind them).
Next, have the students with "moons" turn 90 degrees to their right. "What phase is the moon in now?" (one-quarter, crescent). "How much of the moon is lit?" (one-half). Then have the students turn until their back is to the "sun" and hold the moon up high so that no shadow falls on it. "What phase is it in now?" (full). "How much of the moon is lit?" (still one-half).
Turn the lights on and have the student groups once again work out an explanation of the phases of the moon that they can write down (legibly) on an index card that they then hand in.
Teaching Notes and Tips
Items for further discussion include: lunar eclipses, the "dark" side of the moon, whether it's possible to see a crescent moon directly overhead at midnight.
References and Resources
- A Private Universe Project (more info) : A very similar version of this exercise, intended for young kids, includes excellent questions that could be substituted for the index-card exercise that will help reveal student misconceptions about moon phases.
- Phases of the Moon (more info) : This site contains a series of visualizations of the sun/moon/Earth system ans of the changing face of the moon in the form of Java applets, forms for field observation of the moon, and a collection of exercises and background material (as .pdf's).