To explore the reason the Moon undergoes phases.
The same side of the Moon always faces the Earth because the Moon makes one revolution around the Earth in the same time it takes for the Moon to make one rotation on its axis. As the Moon revolves around the Earth, you can see different amounts of its surface (but always the same surface). When the Moon is between the Sun and the Earth, we cannot see the Moon's lighted side. This is the New Moon phase. Following the New Moon, you see a slender crescent, then a Quarter Moon, then a gibbous (more than a quarter), and finally the Full Moon. The Moon is said to be waxing as it grows. After the Full Moon, the phases reverse until the Moon is invisible again. As we see less light, the Moon is said to be waning.
1. With the felt-tip pen or marker, section the styrofoam ball into quarters, number them and insert the toothpick at the apex of the quarters.
2. Now develop your model as follows: your body is the Earth; the sectioned styrofoam ball is the Moon; the toothpick is the Moon's axis of rotation; your arm is the force of gravity between the Moon and the Earth. NOTE: In the following procedure, turning your body does not represent the Earth's rotation, which does not affect this demonstration. Instead, it allows you to view the position of the Moon in relation to the Earth as the Moon revolves.
3. Darken the room and turn on the overhead projector or whatever light source is being used to represent the Sun.
4. Stand and face the "Sun". (CAUTION: Avoid looking directly into the lamp.) Grasp the toothpick with the thumb and first finger of your left hand. Hold your arm straight out in front of you and raise it so that the 'Moon" is slightly above your head and directly between you and the "Sun."
Rotate the toothpick so that quarters 1 and 2 of the "Moon" are facing you. Sides 3 and 4 are facing the "Sun." Shade in what the Moon looks like to you from this position on the diagram below for Position 1.
5. Keeping the "Moon" above your head, move it about 45o to the left and toward your body by bending your left elbow as seen in the drawing below. Shade in Position 2 on the previous diagram. Which side is lighted, the right or the left?
6. With the toothpick, rotate the "Moon" one quarter turn (90o) in a counterclockwise direction.
7. Now turn your body one quarter turn (90o) to your left. Return your left arm to its original position. Shade in the dark area in Position 3 above. Which quarters of the "Moon" - 1 and 2 or 3 and 4 - are facing you?
8. Continue moving the "Moon" and the "Earth" (your body), repeating steps 5, 6, and 7 until you arrive back to Position 1. Sketch the "Moon" as seen in Positions 4 through 8. Be sure to note whether the darkness is on the right or left. Note which quarters -1 and 2 or 3 and 4 - are always visible from the "Earth."
1. Name and describe the appearance of the eight phases of the Moon in the order in which they occur, starting with the New Moon.
2. Why is only one side of the Moon visible from the Earth?
3. Sometimes eclipses are produced when the shadow of the Moon
falls on the Earth (solar eclipse) or when the Moon moves
through the Earth's shadow (lunar eclipse). At what Moon
phase is a lunar eclipse possible? At what Moon phase is a
solar eclipse possible?
