Wax On, Wane Off
By John Cowens

The moon is our planet's only natural satellite. It has a diameter about a quarter that of Earth's and takes about 27.3 days (a month or so) to revolve around Earth at an average distance of 240,000 miles (384,000 kilometers).

When observed from a telescope, the moon appears to have over 30,000 craters.

The changing figures of the waxing and waning moon are among the most conspicuous of celestial phenomena and were some of the first to be understood. The moon is a dark globe shining only by reflected light. As it revolves around the earth, its sunlit hemisphere is presented to us in successively increasing or diminishing amounts.

It's just a phase
It's the new moon that passes between the sun and the earth, and its dark hemisphere faces toward us. The moon is invisible at this phase except when it happens to cross directly in front of the sun's disk, causing an eclipse of the sun. On the second evening after the new phase, the thin crescent moon is most likely to be seen in the west after sundown; this was the signal for the beginning of the new month in the early lunar calendars. The crescent becomes thicker night after night, until at the first quarter phases the bulging sunrise line gives the moon a lopsided appearance. Finally, a round full moon is seen rising in the east at about nightfall.

The phases are repeated thereafter in reverse order as the sunset line moves across the disk; these are gibbous, last quarter and new moon again. The moon's age is the interval at any time since the preceding new moon.

Lunar lesson #1
Materials:

• shadeless lamp with a 100 watt light bulb


• tennis ball (or equivalent)


• sharpened pencil


• light gray tempera paint

Procedure:

1. Paint the tennis ball and allow it to dry. When it's completely dry, push a sharpened pencil into the tennis ball. This will be the "moon."
2. Tell students that your head will portray Earth.
3. Place the lamp in the middle of your classroom and and turn it on.
4. Turn off the rest of your classroom's lights.
5. Hold the moon in your extended right hand and place it slightly above your head so that no edges are illuminated – this is New Moon. If you place the moon at eye level, the shadow will be cast onto your face and will demonstrate a solar eclipse.
6. Move the moon slowly in a counterclockwise direction. The moment an angle between the earth, sun and moon are created, an edge of the moon then becomes illuminated – this is Waxing Crescent Moon.

7. Move the moon in the same direction until a right angle (90 degrees) between the earth, sun and moon is formed – this is First Quarter.
8. Continue moving the moon in the same direction until an angle of approximately 135 degrees is formed – Waxing Gibbous Moon. The illuminated "moon" is shaped like a football or oval.
9. As you continue to move the moon counterclockwise, a 180-degree angle will form and a Full Moon will appear if the moon is higher than your head. If the moon is held at eye level, a lunar eclipse occurs.
10. As you continue to move the moon counterclockwise, the Full Moon reverses its cycle to the following phases: Waning Gibbous Moon, Last Quarter Moon, Waning Crescent Moon and New Moon.

Questions:

1. What do you think it would be like to have several moons revolving around Earth? Would it change your calendar? Poetry? Tides?
2. What views do you think astronauts have of Earth and the moon as they orbit Earth?
3. Would the moon phases change if the moon revolved around Earth in the opposite direction? How?
4. From Earth, does Venus go through phases?
5. From Mars, does Earth go through phases?
6. Where else could you go to observe phases of other planets?

Lunar lesson #2
Materials:

• small cardboard box


• black construction paper


• glue


• scissors


• two-inch STYROFOAM® ball


• penlight


• masking tape


• modeling clay


• black thread


• X-Acto knife


• straightened paper clip

Procedure:

1. Cut and glue black construction paper to completely cover the inside of the cardboard box including the lid.
2. Cut a piece of black thread about four inches long (10 cm). Take the straightened paper clip and poke a hole in the ball deep enough to stuff one inch of black thread (2.5 cm) into it, apply a few drops of glue and allow it to dry completely.
3. Tape or glue the free end of the thread to the center of the inside lid so that it is suspended in the center of the cardboard box.
4. Place the light end of the penlight against one of the outside short ends of the box. Draw a circle the size of the penlight on the box. Remove the penlight and carefully cut out the drawn circle. Then, secure the penlight with masking tape and modeling clay so it faces into the box through the larger hole on the short side of the box.
5. Cut five small eye holes (1 cm x 1 cm) into the sides of the box. Two should be on each of the long sides and one at the foot of the box, located just beneath the penlight.
6. Seal all of the edges with masking tape and make sure no light shows through.
7. Turn the flashlight on and look through each small hole.

Explanation:
In this simulation, the light from the penlight represented the sun, the STYROFOAM ball was the moon and the five small holes in the box represented your observations of the moon from different places on earth. As the moon travels around the earth, different sections of the moon reflect the sunlight – these are the moon's phases. I hope your students will now look at the moon in a new light.

Here are some lunar websites:

John Cowens teaches sixth grade at Fleming Middle School in Grants Pass, OR.

Updated September 2009
February 2006, Vol.36, No.5