We have all seen the moon change its shape throughout the month as it goes through its phases. In one month, the moon passes from invisibility to fullness and then back again. Most people, however, do not know much about these phases. You can learn and teach about why the phases occur and how to keep track of the phases over the course of a month. With a little effort, you can learn to teach the phases of the moon to students of any age and any background.
Familiarize yourself with the vocabulary associated with lunar phases. You need to know the terms "new moon," "waxing crescent," "first quarter," "waxing gibbous," "full moon," "waning gibbous," "last (or third) quarter" and "waning crescent."
Learn the timing of the moon's phases. The entire lunar cycle takes about 29 days, and you can figure out which phase occurs at which time by observing the moon from night to night or by consulting a calendar.
Show the moon to your students over the course of a month. It's true that everyone has seen the moon, but very few people really take the time to observe its shape over time. Have your students keep a "moon log" in which they draw the moon's shape every night for a month.
You can explain why the moon shows the different phases using simple equipment. Get two small balls (representing Earth and the moon) and a bright flashlight (representing the sun). Shine the flashlight on the Earth ball and move the moon ball to different positions relative to the Earth ball. Have the students name the resulting moon phases at each position.
Have the students draw diagrams of the sun, moon and Earth for the different phases of the moon. Students should be able to distinguish new, crescent, gibbous and full phases easily from the positions.
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Have the students manipulate the balls and flashlight in the demonstration, helping them gain a better idea of the scientific concepts.
If you have more advanced students, you can bring up the concept of "Earth-shine": the barely visible and dark disc of the moon seen when it is in its crescent phase.
It can be hard to picture the relationships between the sun, Earth and moon without explicit demonstrations. Make sure your students understand the demonstration before proceeding.