Model the Phases of the Moon
PREPARE: Cut a large piece of cardboard into a 20" (or larger)
square. Draw a nine-inch and a nineteen-inch circle. Draw a
vertical, horizontal, and two diagonal
lines as shown. Cut out the nine-inch
circle.
Locate the tops in the materials kit. Color each top with a permanent pen so that half the
top is black. Insert the tops into the cardboard where shown by small circles ( ). Turn the
tops so that the dark sides face the same side of the square.
Model the phases of the Moon with tops. Show students the prepared cardboard with the
tops attached.
Ask a volunteer to place the tops over his
head. Orient the tops so that the white side is
toward any source of light (window, projector,
or flashlight) in the room.
Ask the student to face the light source. Have
students name the phase of the Moon seen by
the student (new moon).
Ask the student to turn to the left. Ask
students to name this phase (first quarter).
Have the student turn again and students will say he is seeing a full moon. One more turn
and the student sees the last quarter.
TEACHER BACKGROUND
From Earth, the moon looks like a flat disk that is illuminated by light from the Sun. It is
actually a sphere which is always half illuminated by the Sun.
The phases of the Moon are the result of the relative positions of the Earth, Moon and Sun
New Moon occurs when the Moon is between the Sun and the Earth. Full moon occurs when
the Earth is between the Sun and the Moon. The First Quarter and the Last Quarter occur
when the Sun and Moon are about 90 degrees apart in the sky. These two phases are called
First Quarter and Last Quarter because they occur when the Moon is one-quarter and
three-quarters of the way along its orbit from New Moon to New Moon.
Although the process is continuous, we can identify eight steps, or phases, in the process.
New Moon - The Moon's unilluminated side is facing the Earth. The Moon is not visible.
Waxing Crescent - The Moon appears to be partly but less than one-half illuminated
by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.
QUARTER
MOON
First Quarter - One-half of the Moon appears to be illuminated by direct sunlight.
The fraction of the Moon's disk that is illuminated is increasing.
Waxing Gibbous - The Moon appears to be more than one-half but not fully
illuminated. The fraction of the Moon's disk that is illuminated is increasing.
FULL MOON
Full Moon - The Moon's illuminated side is facing the Earth. The Moon appears to be
completely illuminated by direct sunlight.
Waning Gibbous - The Moon appears to be more than one-half but not fully
illuminated by direct sunlight. The illuminated part of the Moon's disk is decreasing.
QUARTER
MOON
Last Quarter - One-half of the Moon appears to be illuminated by direct sunlight.
The fraction of the Moon's disk that is illuminated is decreasing.
Waning Crescent - The Moon appears to be partly but less than one-half illuminated
by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.
Following waning crescent is New Moon, beginning a repetition of the complete phase cycle
of 29.5 days average duration. The time in days counted from the time of New Moon is called
the Moon's "age". Each complete cycle of phases is called a "lunation".