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Astronomy for ages 13+
Moon Phase: The Moon's Visible Lighted Surface
Purpose: To determine the cause of the phase of the Moon called the new
moon.
Materials
walnut-size piece of modeling clay
pencil
flashlight
Procedure
1. Shape the clay into a ball and stick it on the point of the pencil.
The clay ball is the model Moon.
2. In a darkened room, hold the flashlight at arm's length and shine the light
toward your face.
3. Hold the model Moon midway between you and the light with the model aligned
with the light bulb and slightly above it.
4. Observe the surface of the clay ball.
Results
The light is very bright and the surface of the ball
is difficult to see.
Why?
The Moon shines because it reflects light from the Sun. The side of the Moon
facing the Sun is always sunlit. The side away from the Sun is always dark.
As the Moon orbits Earth, an observer on Earth seed
different portions of the Moon. The appearance of the illuminated surface
of the Moon facing Earth is called a phase of the Moon. The Moon's orbit is at
an angle of about 5 degrees to the ecliptic (plane of Earth's orbit). Thus as
seen from Earth, it usually appears to pass above or below the Sun's disk. When
the Moon is in conjunction with the Sun, the side facing Earth is not
illuminated. This phase is referred to as the new moon. The new moon rises with
the Sun in the east and sets with the Sun in the west.
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