N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 7
Earth/Moon Systems
Spring 2006
EARTH/MOON SYSTEMS
Students in elementary school studied the planets, sun and cycles, including lunar
and seasonal. The 5th grade student identified the physical characteristics of the
Earth and compared them to the characteristics of the moon. They also identified
gravity as the force that keeps the planets in orbit around the sun and the moon in
orbit around the Earth. The 6th grade student identified characteristics of our
solar system, including the sun, planets, meteorites, comets, asteroids and moons.
The 7th grade student will explore and learn how the earth, sun and moon interact
as part of a system to cause changes in seasons, length of day, and moon phases.
Although students will study lunar cycles in 8th grade, 7th graders will not have
studied lunar cycles since 5th grade. The 8th grade curriculum does not include a
study of the causes of seasons or length of day, therefore it is critical that
students understand this concept in 7th grade. Eighth grade teachers will cover
tides as a part of their earth systems unit.
Positions of the Earth, Sun and Moon
Students should understand that Earth moves along a path around the Sun. This
motion of the earth is called revolution. It takes the earth one year to complete
its journey around the sun in a path called an orbit. The orbit is oval not round. It
takes 365 ¼ days for Earth to make one revolution around the sun. We don’t
ignore the ¼ day as after four years the quarters add up to one day and we have a
“leap year”. A day in February is added at this time, giving February 29 days
instead of 28.
The Earth’s axis is an imaginary line that runs through the center. The Earth spins
or rotates around its axis. This rotation takes about 24 hours which marks the
length of a day on Earth. The earth rotates from west to east, or counterclockwise. As the earth rotates daily, the earth is tilted at an angle of 23.5o.
The moon revolves around the Earth in an orbit that takes just under 30 days. The
moon rotates on its axis at the same rate. As a result, we always see the same side
of the moon from Earth.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 7
Earth/Moon Systems
Spring 2006
Seasons
Students often erroneously associate the changes in seasonal temperatures to the
proximity or nearness of the earth to the sun. They think the earth is closer to
the sun in the summer than in the winter. The earth is actually closer to the sun in
the winter months in the northern hemisphere. The cause of seasons has nothing to
do with the distance the earth is from the sun. Seasons are caused primarily by
the 23.5 degree tilt of the earth on its axis. Around June 21, or summer solstice,
the North Pole is tilted towards the sun and the sun is positioned directly over the
Tropic of Cancer at 23.5 degrees north latitude. This tilt of the Northern
Hemisphere towards the sun causes longer daylight hours and causes the Northern
Hemisphere to heat up because it receives more direct sunlight.
The summer solstice is when the earth experiences its longest day. Although June
21 or 22 mark the first day of summer in the Northern Hemisphere, the Southern
Hemisphere experiences the opposite season. The Northern Hemisphere
experiences winter solstice around December 22. This is the first day of winter
and the shortest day of the year. The Earth has now traveled in its orbit to a
position where the North Pole is tilted away from the sun. The sun’s rays are more
spread out as they travel towards the northern hemisphere, and there are fewer
daylight hours. The Southern Hemisphere is experiencing summer at this time.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 7
Earth/Moon Systems
Spring 2006
The time when the sun is directly above the equator is called an equinox. This
means there are equal numbers of day and night hours. Equinoxes occur in March
and September, spring and fall. Spring equinox occurs around March 21 and
autumnal or fall equinox occurs around September 23.
The following diagram depicts Earth in its orbit at the time of the solstices and
equinoxes. This diagram is a 2-dimensional model and this would be a good
opportunity to discuss the limitations of such a model, including the fact that the
Earth is depicted to be significantly closer to the sun at certain periods in its
revolution in diagrams such as this:
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 7
Earth/Moon Systems
Spring 2006
The following diagram illustrates the differences in angle of sunlight at different
times of the year or why we have seasons:
Phases of the Moon
Students often have the misconception that the moon produces its own light. They
should understand the reason the moon appears lit at night is because it is
reflecting sunlight, as is every object in the universe except for stars. Daily
observations of the moon reveal a slight change in the moon’s appearance from one
day to the next. These changes are due to the revolution of the moon around the
earth and the earth’s revolution around the sun. These changes are known as the
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 7
Earth/Moon Systems
Spring 2006
phases of the moon. The four most known phases are the full moon, first quarter,
the new moon, and the third or last quarter. A full moon occurs when the earth is
between the sun and the moon. A new moon occurs when the moon is between the
sun and the earth. The entire lunar cycle occurs once every 27.3 days.
The moon appears to travel from east to west across the southern sky at night in
the northern hemisphere. The same side of the moon is always facing earth
because the moon rotates at the same rate that it revolves around the earth. If
the moon appears greater than one-half illuminated, it is known as a gibbous moon.
If the moon appears to be less than one-half illuminated, then it is called a
crescent moon. If the moon appears to be getting bigger each night it is said to be
waxing. If the moon appears to be getting smaller each night then it is said to be
waning. Students need to be able to identify the eight major phases: new moon,
waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last
quarter, waning crescent, new moon. Students can keep a log of changes in the
shape of the moon over a period of time.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Moon Phase
new moon
Diagram
Unit 7
Earth/Moon Systems
Spring 2006
Explanation
no moon is visible as the sunlit portion does
not face Earth
waxing
crescent
seen as a small crescent / slice of the moon
as the sunlit portion is increasing in size from
day to day
first quarter
seen as one half of the moon as the sunlit
portion continues to increase in size from day
to day
Note: The first quarter moon looks like a
right half of a circle.
seen as a greater than quarter but less than
a full moon as the sunlit portion is increasing
in size from day to day
waxing gibbous
full moon
the entire sunlit side of the moon is visible
waning gibbous
seen as greater than a quarter but less than
a full moon as the sunlit portion begins to
decrease in size from day to day
last quarter
seen as one half of the moon is lit as the
sunlit portion is decreasing in size from day
to day
Note: The first quarter moon looks like a
left half of a circle.
seen as a tiny slice of the moon as the sunlit
portion continues to decrease in size from
day to day
waning
crescent
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 7
Earth/Moon Systems
Spring 2006
Eclipses
As the moon travels in its orbit around the Earth, it sometimes moves into a
position that causes an eclipse to occur. An eclipse occurs when one object in
space casts a shadow on another. When the the moon moves directly between the
Earth and Sun, the moon casts a shadow on the Earth. This results in a solar
eclipse. During a solar eclipse, people on Earth who are in the moon’s shadow can’t
see the sun. Total solar eclipses occur when the moon blocks the whole sun from
view, and partial solar eclipses occur when only a portion of the sun is blocked from
view. Students should understand that a solar eclipse can only occur during a new
moon phase.
A lunar eclipse can occur during a full moon phase, but only if the Sun, Earth, and
moon are exactly lined up. It happens when Earth casts a shadow on the moon.
These eclipses are visible over the entire nighttime side of the Earth.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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