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Moon phases
chapter 1
 What causes the moon to change in appearance
and position in the sky?
Standard 1: Objective 1 6th Grade
Text Structure: Sequence

Doesn’t it seem as if the moon’s shape changes night after

night? As the moon orbits –the curved path of a celestial
object or spacecraft around a star or planet—Earth, it appears
as though the moon is changing its shape in the sky. This is
because as the moon changes its position, the amount of
sunlight reflected back to Earth also changes. The moon
sometimes appears fully lit and sometimes completely dark.
Most of the time we see it partially lit.

The North and South Poles mark Earth’s axis. Earth rotates
on its axis every 24 hours. Another major movement of
planets and moons is revolution–the circling of an object in
space around another object in space. It takes a year for
earth, or 365.25 days, to revolve around the sun. It takes the
moon about 29 days to revolve around Earth. This path is
called an orbit.

Just as Earth rotates on its axis and revolves around the sun,
the moon rotates on its axis and revolves around Earth. The
moon’s revolution or orbit around Earth is responsible for the
changes in its appearance. It takes the moon about one
month to orbit Earth. It also takes the same amount of time
for the moon to complete one axis of rotation–the spinning of
objects around an imaginary center line—the two motions take
the same amount of time, so this is why the same side of the
moon always faces the Earth.

"FullMoon2010" by Gregory H. Revera. Licensed under

Creative Commons Attribution-Share Alike 3.0 via Wikimedia
Commons -
http://commons.wikimedia.org/wiki/File:FullMoon2010.jpg#mediavi
ewer/File:FullMoon2010.jpg

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 When the moon is between Earth
and the sun, we observe a new
moon— the side of the moon
facing Earth is completely dark.
On the day of a new moon, the
moon rises when the sun rises
and sets when the sun sets. The
new moon only takes place
during daylight hours. As the
moon revolves around Earth, we
are able to see more of the lit
portion of the moon.

We start by seeing a waxing

crescent – the lit portion on the
right side of the moon. Sometimes
you can just barely make out the
round outline of the whole moon
at crescent phase. This is
because some sunlight reflects off
the Earth and hits the moon, a
phenomena called "Earth shine."
The waxing crescent moon phase
lasts for about six days.

When it appears that the right half

of the moon is lit, we call this the
first-quarter. This occurs when the
moon has completed one quarter of
its orbit around Earth with respect
to the sun. Even though the moon
will be at this place in its orbit for
just a moment, the moon appears
half lit for about a day.

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 The lit portion appears to continue to wax –
grow bigger—into a waxing gibbous phase
–more than half-lit but less than full.

A full moon occurs when the whole

side of the moon facing Earth is lit,
this happens when Earth is between
the moon and the Sun.

After a full moon, the lit portion starts to wane—get smaller.

The moon will begin to look smaller as we see less and less
of the lighted side. This will first show the waning gibbous
phase followed by the third-quarter moon. As it continues to
wane, we will see a waning crescent moon for about six days
until the cycle is completed and we have new moon again.
This whole progression of phases takes 29.5 days or about a
month. After a complete phase cycle, the cycle begins again

with a new moon.

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How does the position of Earth, the moon, and
the sun create the appearance of the moon’s
phases?
Standard 1: Objective 2
Grade 6
Text Structure: Compare and Contrast

The moon is Earth’s only natural satellite--a body that moves

or revolves around a larger body in space. The moon is kept
in orbit around Earth by the same gravitational force that
keeps Earth orbiting the sun. The moon is 3,476 km in
diameter, about one-fourth the diameter of Earth. The mass of
the moon is only 1.23 % the mass of Earth. Gravity on the
moon is only one-sixth as strong as it is on Earth due to this
combination of mass and diameter. If you weigh 120 pounds
on Earth, how much would you weigh on the moon? That’s
right! You would weigh 20 pounds. You can jump six times as
high on the Moon as you can on Earth if you weren’t wearing
a space suit. The moon is also not as dense as Earth.

The moon rotates on its axis in the same amount of time it

takes it to make one orbit around Earth. What does this
mean? The same side of the Moon always faces Earth, so we
always see that side of the Moon in the sky. The side of the
Moon that always faces Earth is called the near side. The
side of the moon that always faces away from Earth is called
the far side. From Earth, people have only seen the moon's

http://goo.gl/FY657T

near side. The far side has only been seen by spacecraft and
Apollo astronauts as they orbited the moon.

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 The rotation of Earth gives the sun the appearance of moving
across the sky. The sun is actually in the same place in the
sky. As Earth rotates, it brings the sun in and out of view
giving us daylight and darkness. Remember the sun is not
moving, it is the rotation of earth that brings the sun into
view. When sunlight is hitting the part of the moon that is
facing away from Earth, we see only the dark side of the
moon. When we cannot see any part of the moon’s lighted
reflection, the moon is invisible to us. We call this a New
Moon. The New Moon phase only takes place during daylight
hours. As Earth rotates to nighttime, the New Moon is no
longer in view, having disappeared behind the horizon.

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 23
Seasons
chapter 2
 What causes the changing seasons?
Standard 2: Objective 1 & 2
Grade 6
Text Structure: Description (Informative)

The days are getting warmer, flowers begin to bloom. The sun
appears higher in the sky, and daylight lasts longer. Spring
seems like a fresh, new beginning. What causes these
welcome changes?

There are two factors that cause the seasons to occur. First is
that the Earth revolves in an orbit - the path a planet takes
around an object. The orbit of Earth around the sun is nearly
circular. As Earth moves throughout the year to new positions
around the sun, the movement results in our four seasons:
summer, autumn, winter, and spring.

The distance from the sun doesn’t have much effect on the
heating and cooling of Earth. In fact, we are closest to the
sun during winter in the Northern Hemisphere. So, why do we
feel coldest when Earth is closest to the sun? The second
important fact that helps us understand the changing seasons
is Earth’s tilt—a 23.5 degree angle—and Earth’s axis of
rotation— imaginary poles on which Earth spins. It is this tilt

that causes seasons.

http://goo.gl/FQcNBS

As Earth revolves around the sun, it maintains this tilt, and it

always points in the same direction toward the North Star
(Polaris). The combination of the Earth’s revolution around the

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sun and Earth’s 23.5 degree angle tilt are the reasons we
have seasons.

Northern Hemisphere Summer

The North Pole is tilted towards the sun and the sun's rays
strike the Northern Hemisphere more directly in summer. At
the summer solstice, June 21, the sun's rays hit the Earth
most directly along the Tropic of Cancer (23.5oN). When it is
summer solstice in the Northern Hemisphere, it is winter
solstice in the Southern Hemisphere.

Indirect

http://goo.gl/zF5aOd
http://goo.gl/6eqeWg

Northern Hemisphere Winter

Winter solstice for the Northern Hemisphere happens on
December 21. The tilt of Earth's axis leans away from the
sun. Light from the sun is spread out over a larger area, so
that area isn't heated as much. With fewer daylight hours in
winter, there is also less time for the sun to warm the area.

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 When it is winter in the Northern Hemisphere, it is summer in
the Southern Hemisphere.

Interactive Seasons: http://goo.gl/XT8X

During the summer, areas north of the equator experience

longer days and shorter nights. This is because at this time
the Northern Hemisphere is tilted towards the sun and
receives more direct rays. At the same time in the Southern
Hemisphere it is winter and locations will have longer nights
and shorter days. This is because this Hemisphere is pointed
away from the sun and receives less direct rays.

Summer occurs in the hemisphere that is tilted toward the

sun. This is when the sun appears high in the sky. Its
radiation strikes Earth more directly for longer periods of time.
The hemisphere that is receiving less radiation experiences
winter.
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Equinox
There are two times during the year when the Northern and
Southern Hemisphere have the same amount of daylight. They
are March 21st and September 21st. These mark the first
official days of spring and fall. The tilt of Earth affects the
height of the sun in the sky and the length of daylight.

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