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Jump to: Intro,
What the Moon is like, Composition,
Conditions, Page 2:
Movement of the Moon,
Phases, Eclipses
MOVEMENT OF THE
MOON:
Following an elliptical orbit, the
moon travels around the earth at 2,300 miles per hours. One trip or
revolution is 1.4 million miles. The moon also travels with the
earth as it circles the sun. The moon moves west to east on our sky,
but seems to move east to west because the earth spins much faster
than the move can revolve around the earth. Since the orbit is oval
shaped, the moon is not always the same distance away from the
earth. The point where it comes the closes to the earth is called
perigee. This is 221,456 miles away. The farthest point, apogee, is
252,711 miles. The gravitational pull keeps the earth's moon in its
orbit. The moon's revolution around earth is measured in synodic
months and sidereal months. A synodic month is about 29 1/2 days
long, and is the period from one new moon to the next new moon. This
is the amount of time it takes to revolve around the earth relative
to the sun. A synodic month is one full day on the moon. The lunar
day is classified in to two weeks of light and two weeks of
darkness. A sidereal month is about 27 1/3 days, and is the amount
of time it takes for the moon to travel around the earth in relation
to stars.
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ROTATION:
The moon rotates on its axis only once during its trip around the
earth. The moon rotates from the west to the east, the same
direction that it travels around the earth. At its equator it
rotates about 10 miles per hour. Sometimes a short distance around
the edge of the moon can be seen, called the limb. It seems to swing
up and down and from side to side during each revolution. These type
of motions are called liberations. They are caused by changes in the
moon's speed of revolution and by a tilt of 5 degrees. Liberations
allow us to see about 59 percent of the moon.
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PHASES:
The moon has many phases. During a
synodic month we see the moon change from a crescent to a full
circle and back. These seemingly changes in shape and size are due
to different lighting conditions. Different amounts of sunlight is
reflected by the sun to the earth, causing these phases. The shape
appears to change because we see different parts of the moon's
surface as it makes its orbit. When the moon is in between the sun
and earth, its far side is turned away from the earth. It seems to
be a darkened phase and is called a new moon. In the new moon phase,
the side of the moon is lighted by earthshine, sunlight that is
reflected from the earth to the moon. A day after the new moon, a
thins slice of light can be seen, The line between the sunlit part
and the dark part is called the terminator. Each day, more and more
of the moon's sunlit side is seen. After seven days, we see half of
a full moon. This half circle is exposed to the sun and can be seen
from the earth. It is called the first quarter. Seven days after the
first quarter, the moon moves to where the earth is between it and
the sun. This phase is the full moon. Seven days after the full
moon, we see a half of a full moon once again. This is known as the
last or third quarter. After one more week, the moon returns to the
new moon phase. As the moon changes from a new moon to a full, it is
called waxing. During the period from full to new, the moon is
waning. When it seems to be smaller than half of a moon, it is
called a crescent. When it seems to be larger than half of a moon,
it is called a gibbous. The moon rises and sets at varying times.
The moon rises above the horizon. With each passing day, the moon
rises about 50 minutes later and drops about 12 degrees. By the end
of a week, the moon rises at noon and sets at midnight. During the
full moon, it rises as the sun sets and sets as the sun rises.
During the last quarter, it rises at midnight and sets at noon.
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ECLIPSES:
When a full moon passes through the
earth's shadow, we see an eclipse of the moon. During a lunar
eclipse, the moon is a dark reddish color. It is lighted by faint
red rays from the sun that have been refracted by the atmosphere of
earth. During another eclipse, the moon passes directly between the
earth and the sun. When part of the sun is hidden by the moon. we
see a solar eclipse. (For more information on solar eclipses, visit
the SUN)
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