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UNIT 3:
Chapter 7: The Earth-Moon-Sun System
I. Earth in Space
A. Earth’s Size and Shape
1. Early astronomers like
Aristotle said Earth was
spherical in shape
a. Evidenced by shadow of
Earth on Moon during
eclipse
b. People in different parts
of world see different stars
above their horizons
2. Curvature of Earth is evident when looking at
objects far away
3. Modern images of the Earth from space
4. Gravity was force that caused it to form
spherical shape as Earth formed.
5. Earth’s Physical Properties
B. Earth’s Magnetic Field
1. Earth has magnetic field similar to a bar
magnet
a. Protects us from
harmful radiation from
Sun
b. Magnetic field
concentrated at the
poles
2. Location of poles changes slowly over time
3. Aurora borealis (northern lights) caused by
reaction of charged particles from sun and Earth’s
magnetic field
C. Earth Orbits the Sun
1. Earth orbits the Sun in an elliptical orbit
(“squashed circle”)
a. Distance of Earth to sun varies during year
b. Closest to the Earth in January and furthest away
in July
2. Earth is considered a planet like Venus, Mars,
and Jupiter.
a. Conditions on
different planets
depend on how far
from the Sun they
are and their size
b. Mars is most like
the Earth
II. Time and Seasons
A. Measuring Time on Earth
1. People have used
the position and
movements of Sun
and Moon to
measure time for
thousands of years
2. Earth’s movements measure time
a. Earth spins and makes one complete
rotation every 24 hours.
b. Earth spins 360° in 24 hours- equals 15° every
hour.
c. This led to time zones every 15°
d. International Date Line- falls down through the
Pacific Ocean.
3. The spinning (rotation) motion of Earth enables
you to measure the passing hours of the day.
4. The motion (revolution) of Earth around the
Sun enables you to measure passing of years
B. Why do Seasons change?
1. The distance between the Earth and the
Sun varies throughout the year.
2. Seasons caused by Earth’s rotation, its
revolution, and the tilt of its axis (23.5°)
3. Angle at which sunlight hits the Earth determines
warming effect
a. Higher angles produce more warming
b. Lower angles produce less warming
4. More hours of sunlight in summer than winter
5. Equinox- when number of daylight hours equals
number of nighttime hours
a. Spring equinoxMarch 21st
b. Fall equinoxSeptember 22
6. Solstice- sun reaches greatest distance north or
south of equator
a. Summer
solstice- June 21st
b. Winter solsticeDecember 21st
III. Earth’s Moon
A. Movement of the Moon
1. The Moon revolves around the Earth
every 27.3 days (a sidereal month)
2. The same side
of the moon faces
Earth because it
also rotates one
complete revolution
in 27.3 days
B. How does the Moon affect the Earth?
1. Tides- caused by gravitational pull of the
Sun and Moon
a. Moon’s gravity has
more effect than Sun
because it is much
closer to Earth
b. As Earth rotates,
different locations pass
through high and low
tides
C. Moonlight
1. Moon phases- are changing appearances
of the Moon as seen from Earth
a. New Moon- occurs when
Moon is between Earth and
Sun. Moon is in sky,but cannot
be seen
b. Waxing phases- occurs after new moon. Lighted
portion becomes larger each night
c. Waning phases- Lighted portion begins to get
smaller
d. Full Moon- occurs when we see all of Moon’s
lighted side
2. The word month comes from the same root word
as Moon
D. Eclipses
1. Solar eclipses- occurs when
Moon moves directly between Sun
and Earth and casts shadow on
part of Earth
2. Lunar eclipse- occurs when Earth’s shadow falls
on the Moon
E. The Moon’s Surface
1. Moon’s surface includes many different
surface features
2. Craters- depressions on the Moon formed
by impact of meteorites, asteroids, and
comets
3. Maria- dark-colored, relatively flat regions formed
by igneous rocks 93 to 4 billion years old)
4. Regolith- few centimeters thick to over 40 m
thick. Various from coarse to dust-like
F. Moon’s Interior- Model shows crust 60 km - 150
km thick with solid mantle 1000 km deep with
partially molten core
G. Exploring the Moon- has included both manned
and non-manned spacecraft
H. Origin of the Moon
1. Prior to Apollo mission there were 3
different theories
2. After Apollo mission all three theories found
incorrect
3. Led to new theory- Giant Impact Theory
a. Moon formed 4.6 billion years ago
b. Mars sized object collided with Earth
c. Debris thrown into orbit and condensed into
large mass, forming the moon
d. Moon’s
composition likes
Earth’s mantle