Text: Rotation and Revolution: The Moon 1. Have a student stand in front of the class facing the back of the room. Have them slowly turn counterclockwise a full 360 degrees. Have them describe what they see as they turn: the back of the room, the left side (as viewed from the front of the room), the front, the right side, and then the back again). Explain that the student has just rotated once and as the student turned they saw, in turn, all sides of the room. This is rotation. 2. Now have another student stand in front of the class, facing the back of the room, toward the class. Have the first student move in a circle, counterclockwise, around the second student, always facing the back of the room. The first student starts out in back of the second student, then to their right, then in front, then to their left, and then back in back of them. This is revolution. 3. Now ask the students whether or not the first student rotated while revolving around the second student: No, they always faced the back of the room. Now, have the first student revolve around the second student, but this time always facing the second student. As they move around the second student, have them describe what part of the room they are seeing: first the back, then the left side, then the front, then the back again --- they rotated once as they revolved around the second student! 4. You can now discuss the Moon as it goes around the Earth. Since we always see the same side of the Moon, this implies that the Moon rotates once as it revolves around the Earth. The Lunar Month 1. You can use the diagram in Figure 1(Sun, Moon, and Earth) or continue this as a demonstration, using a third student as the Sun. 2. Student 1 = Sun. student 2 = Earth, student 3 =Moon. Have student 3 revolve and rotate around student 2 once (2 motionless). This is how long takes for the Moon to go once around the Earth, 27 1/3 days. However, in reality, the Earth is revolving around the Sun. In 27 1/3 day, it has one nearly 1/12 of the way around the Sun. Have student 2 demonstrate this by having them move a little counterclockwise around student 1, the Sun. 3. Now, bring back student 3. Line up the students Sun, Earth, Moon (1, 2, 3) with the Moon (student 3) facing the Sun and the back of the room. As seen from the Earth, this is full Moon. Now, as student 3 rotates and revolves around the Earth, have the Earth revolve slowly around the Sun. Have the Moon revolve and rotate once, so they are facing the back of the room again --- as can be seen in Figure 1, the three students are no longer in a straight line, it is not full Moon. The Moon must continue to revolve and rotate about 1/12 of an orbit until the Sun, Earth, and Moon are aligned again. This is defined as one month, the time from full Moon to full Moon, 29 1/2 days.

See Also:

Source: