EJS Moon Phases Model
General Description
This program illustrates how the appearance of the moon changes depending
on the position of the moon relative to Earth and the sun. The left window
shows the earth (at the center) and the moon, as well as a circle tracing
out the moon's orbit. The sun is far to the right in this picture and
therefore the right side of the earth and moon are bright while the left
sides are dark. A glowing band of light shows the portion of the moon
visible from earth, as well as the portion of earth from which the moon is
visible. The angle between the sun and moon (as seen from earth) can be
adjusted. A horizon line for an observer on earth can be added and the
time of the observation can be set (which effectively changes the
observer's location on earth in this picture).
The right window shows the appearance of the moon as seen from earth
when the moon is in the position shown in the left window.
Visual Elements
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Orbit Window
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Blue/black disk: Earth.
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White/black disk: the Moon.
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White circle: the Moon's orbit around Earth.
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Yellow arrows: indicate the direction of incoming sunlight. The
sun is far to the right.
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Transparent white band: shows the portion of the Moon that is
visible from Earth as well as the portion of the Earth from which
the Moon is visible.
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Red line: horizon line of observer on Earth (shown only if Horizon
box is checked).
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Moon View Window
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Shows view of Moon as seen from Earth when the Moon is in the
position shown in the Orbit Window.
Controls
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Sun-Earth-Moon Angle (degrees): slider controls the angle between the
sun and moon, as seen from earth. This effectively moves the Moon
around in its orbit as seen in the Orbit Window.
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Time (0 24 h): sets the observation time for an observer whose horizon
is shown by the red line (if the checkbox described below is checked).
Time is in hours, with 0 corresponding to midnight.
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Horizon: if checked the horizon line for an observer on Earth at the
time set by the Time control will be shown as a red line.
Todd K. Timberlake (ttimberlake@berry.edu)