Lesson - Phases of the Moon

As you look in the sky over the course of a month, you should notice a change in the appearance of the moon. The different shapes the moon makes are known as the moon's phases.

Look at the animation of the phases of the moon from Solar Views. Notice how the moon changes over the course of a lunar cycle. When the moon appears as a full circle, we refer to it as a full moon. When the moon appears completely dark, we refer to it as a new moon. A half full moon is a half moon. A moon that is less than half full is referred to as a crescent moon, and a moon that is more than half full is referred to as a gibbous moon. Notice that over the course of a lunar cycle, the amount of lighted area on the moon first increases (or wanes), and then after the new moon increases (or waxes).

1. Can you identify a waxing crescent moon in the animation?
2. Can you identify a waning gibbous moon in the animation?
3. Have you learned from previous classes or experiences the cause of the phases of the moon? If so, describe what you think causes the phases of the moon. Discuss this with your classmates.
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.
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?
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?
7. What would the moon look like if the angle were greater?
8. What would the moon look like if the angle were smaller?
9. What is it called when the shadow of the Earth falls on the Moon?
10. What is it called when the Moon passes between the Earth and the Sun?