Planetary Systems
Unit Readings and Assignments
Name ___________________
Table of Contents
Part 1: Earth in Space
Pages 2-4
Homework Assignment #1
Page 3
Homework Assignment #2
Page 4
Part 2: The Earth, Moon, and Sun System
Pages 5-11
Homework Assignment #3
Page 6
Homework Assignment #4
Page 9
Homework Assignment #5
Page 11
Part 3: The Solar System
Page 12-??
Homework Assignment #6
Page 12
Homework Assignment #7
Page 13
Homework Assignment #8
Page 15
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Part 1: Earth in Space
Day and Night
Day/Night are caused by the rotation of the
Earth. When the Sun is shining on one side of the
Earth, that side is in daylight. The side away from
the Sun is experiencing night. As the Earth rotates
counterclockwise, the Sun rises in the eastern sky and
sets in the western sky. Planets and stars also rise and
set in the night sky is due to the Earth’s rotation. At any
given time, half of the Earth is in day and half in night.
A big misconception among students is that the moon is always up during night.
This is not true, as you will learn later in this unit. As a certain place on Earth is entering
the Sun’s light, we call that sunrise. When that place is leaving the Sun’s light, we call it
sunset. When there are equal amounts of light on either side (as one would see looking at
Earth from space), it is referred to as noon. Opposite of noon is midnight, when the
location on Earth we are referencing is exactly halfway between sunset and sunrise.
However, depending where you are on Earth, you may experience different amounts of
sunlight due to the tilt of the earth’s axis.
Seasons on Earth
Seasons are caused by two factors: Earth’s tilted axis (23.5 degrees) and the fact
it revolves around the Sun. This causes the Earth to be tilted towards and away from the
Sun during the summer and winter months. Because of this tilt, two factors come into play
in heating the Earth’s surface. First, and most importantly, in the summer radiant energy
(heat and light) from the Sun hits the Earth at a more direct angle causing the energy to
be more concentrated in a given area.
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Secondly, areas that are experiencing summer receive the energy for a longer
period of time due to increased day length. These two factors cause mid-latitude and Polar
Regions of our planet to experience energy variations over a 12 month period. While the
equatorial regions also receive energy variations, the Sun’s energy hits these regions at a
relatively direct angle all year long causing it to experience warmer temperatures
throughout the entire year.
Also, it should be noted that the Northern and Southern Hemisphere experience
seasons that are opposite to each other. When the Northern Hemisphere is tilted towards
the Sun and experiencing summer, the Southern Hemisphere is tilted away from the Sun
and experiencing winter. The opposite is true six months later. The spring/fall
relationships have a similar converse relationship.
Homework Assignment #1
Label the Northern and Southern Hemispheres and what seasons they are
experiencing. The axis and equator are drawn in for your convenience
Northern Hemisphere Season: ____________________________
Southern Hemisphere Season: ____________________________
Explain why you chose those seasons…
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Light Concentration and Seasons
Only latitudes between the Tropic of Cancer and Tropic of Capricorn can receive
direct rays. The maximum angle of insolation is 90 degrees. As Latitude increases, the
angle of insolation decreases. The poles are at about 90 degrees North and South. The
maximum angle of insolation, maximum duration, and maximum intensity occur during the
summer. From morning to noon, the angle of insolation increases. The angle of insolation
decreases from noon to evening. As the Sun moves higher in the sky, the length of the
shadow decreases, and as the Sun moves lower in the sky, the length of shadow increases,
causing warmer temperatures when the sun is at its mid-point in the sky.
Think of it this way: if someone were to throw a ball at you and hit you directly, you
would receive more of the ball’s energy than if the ball deflected off you at an angle. This
is the same as far as light hitting you at an angle of insolation of 90 degrees (direct) as
opposed to an angle of insolation of 60 or 30 degrees.
In general, the mornings are cooler and as the Sun’s ray become more direct during
the day and the temperature increases. As the Sun sets, temperatures usually will fall.
When there is a surplus of heat energy, the temperatures go up. When there is a deficit
of heat energy, the temperatures go down. Maximum temperatures never occur at the
time of the maximum angle of insolation. This is because a surplus occurs from June to
August (in northern hemisphere) of heat energy and the temperatures go up. From
December to March, there is a deficit of heat energy, so the temperatures go down.
Homework Assignment #2
Draw the sun at three different angles of insolation: 30, 60, and 90 degrees.
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Part 2: The Earth, Moon, and Sun System
What is Gravity?
Many years ago a young scientist sat beneath an apple tree and an
apple fell on his head. This young person was named Isaac Newton and this
event would shape the rest of his scientific career. He wondered why the
apple fell and if this force, called gravity, affected other objects such as
the planets.
Gravity is one of the four fundamental forces in our universe. It is an attractive
(pulling) force between objects, and the objects can exert a gravity force on one another
without even touching. It is for this reason that gravity is sometimes called the invisible
force. The amount of force between the objects depends on the masses of the objects
and the distance between them. If the mass increases, so does the force of gravity. If
the distance between the objects increases, the force of gravity decreases; but the force
of gravity never goes to zero.
All objects exert their force of gravity (we could even calculate your own personal
“gravity force” if we wished), but in most cases, objects are too small to really concern
ourselves with their affects. The force involves two objects and will change size based
upon the characteristics of the second object. This is not the case with large objects such
as planets, stars and asteroids. What Newton discovered is that the force of gravity was
universal-it behaves the same way everywhere in the universe. The Sun and the planets
have a gravitational pull on each other, but because the Sun is so much more massive, its
gravity dominates the solar system and is the reason why the planets orbit the Sun, not
the other way around. The Earth’s gravity is responsible for keeping our Moon in orbit
around our planet.
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Gravity and Planets – Why are most space objects spherical?
On Earth, we typically say that gravity pulls things straight
downward, but the truth is that gravity actually pulls toward the center of
the Earth. If you look at a globe, vertically downward in Delaware is not
the same direction as vertically downward in Hawaii. So, when talking about
the force of gravity on a global or astronomical scale, it would be more
accurate to say that gravity acts inward, towards the Earth’s center. When our solar
system was forming, there were many small pieces of gas and dust, each having their own
very small amount of gravity. As these small pieces started to stick together, the
combined (now larger and more massive) object increased its gravity and pulled more and
more pieces together from all directions. This caused the formation of objects in a
spherical shape.
Homework Assignment #3
Draw a picture to represent gravity. Do not use any words.
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Defining Tides
A tide is the distortion of the shape of one object (Earth) produced by the
gravitational pull of another nearby object (Moon and Sun). The Sun is the more massive
object and it would appear that it would influence tides on Earth more so than the Moon,
but the Moon is much more influential in tidal action because it is so much closer to the
Earth than the Sun. Even though the Sun exerts a greater gravitational force on the
Earth, its pull is nearly constant over the diameter of the planet. The Moon’s gravitational
pull, on the other hand, varies across the diameter of our planet. It is this variation in the
strength of the Moon’s gravity that influences tides.
Gravity and Tides
The Moon does not simply revolve around the Earth, both the Earth and the Moon
are in motion together and therefore require forces to keep them moving in this circular
pattern. It is the force of gravity that makes these two objects move this way and since
they are locked together by the forces of gravity that they exert on one another, they
are commonly referred to as the Earth-Moon system. Remember that gravity weakens
with distance, so the side of the Earth that is closest to the Moon will experience the
greatest force of gravity and the side farthest from the Moon will experience the
smallest force of gravity. This is outlined in the figure below.
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This difference in the force of gravity causes the Earth and its oceans to become
egg-shaped. This produces tidal bulges on both sides of the Earth, through which the land
masses and oceans pass through on a daily basis. The underlying geology of the land
masses also contributes to the variations in tides associated with particular regions about
the globe. It may also surprise you that both the land and the atmosphere also experience
tides due to gravitational effects.
The Predictable Time Schedule for Tides …
Variations in tides occur around the world due to many factors. The combination of
land (continents) and water create shorelines which can vary from one location to another.
The topography of the coastal area (shape of sea floor and the mouths of bays and rivers)
can also cause great variations in the tides.
Most coastal areas on Earth experience 2 high tides and 2 low tides every day. A 24
hour day is caused by the rotation of the Earth on its axis. As a result, the tide in most
coastal areas of the Earth changes every 6 hours, 12 minutes and 30 seconds.
For example: If the first high tide of the day was 9:00 AM, then a low tide would
be expected at 3:12:30 PM (9:00 AM + 6hrs 12 minutes and 30 seconds.. The second high
tide would be expected at 9:25 PM with the next low tide expected at 3:37:30 AM (9:25
AM + 6 hrs 12 minutes and 30 seconds.. The first high tide of the following day would be
expected at 9:50 AM. This is a very predictable pattern.
The Role of the Sun on Tidal Action
The gravitational attraction between the Moon and the waters of the Earth is the
main cause of the tides, but the Sun certainly plays a part. The tide generating force of
the Sun is about half of the Moon. When the Earth, Moon and Sun are in alignment, the
force is additive. The gravity of the Moon and Sun work together causing extra-high tides
and very low (low) tides. These tides are called Spring tides and occur twice per lunar
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cycle. Spring tides occur during the full and New Moon phases. The highest high tides
occur during the New Moon phase since the Moon and Sun are on the same side of the
Earth and their gravity is pulling in the same direction.
Homework Assignment # 4
The gravity of the
Moon has more of
an affect on tides
than the Sun
because the Moon
is closer. BUT!!
The Sun DOES
have an effect!
During New Moon and Full Moon phases high tides are
higher than other phases because the gravity of the Moon
and Sun “work together”. These are called SPRING TIDES.
During First Quarter and Third Quarter phases high tides
are lower than other phases. These are called NEAP TIDES.
Look at the diagram and explanations above. Do your best to describe why Neap tides
are the lowest high tides.
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If it is high tide in Delaware at 12:00 P.M., what time will the next low tide occur?
_________________
…the next high tide?
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Moon Phases
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Moon Phases and Eclipses
The Moon appears to change shape throughout the month. The Moon is not actually
changing shape, but the part that we see illuminated here from Earth is changing. The
major phases of the Moon include New Moon, Waxing and Waning Crescent, First and Last
Quarter, Waxing and Waning Gibbous and Full Moon. The Moon rotates and revolves
counterclockwise.
The illuminated part of the Moon always points the way to the Sun. If the right
side of the Moon is illuminated, the Sun is on the right. If the left half of the Moon is
illuminated, the Sun is on the left. The phases of the Moon always proceed with the
lighted part of the Moon growing from right to left until the Full Moon, then receding
from the right to left until you reach New Moon. If the Moon is light on the right side, the
light will continue to expand to the left (Waxing). If the Moon is dark on the right side,
the shadow will continue to expand to the left (Waning). The edge of light that moves
across the Moon’s surface is called the terminator. The terminator always moves from
right to left on the Moon’s surface.
The Full Moon occurs when the Moon is on the opposite side of the Sun from the
Earth. In this position, the Moon receives full light on the side of the Moon facing Earth.
The period after the Full Moon up until the New Moon is called a waning Moon because the
visible lighted surface is decreasing. One lunar cycle from New Moon to New Moon lasts
about 29 ½ days.
A lunar eclipse occurs during Full Moon when the Earth’s shadow falls on the Moon.
This would happen every month during Full Moon if the Moon orbited around Earth in the
same plane as the Earth orbits around the Sun. The Moon’s orbit is tilted about 5 degrees
above the Earth-Sun plane. This tilt also moves and rotates which allows eclipses to happen
when the Earth, Sun and Moon end up in a straight line, therefore blocking Sunlight. A
lunar eclipse is visible to an entire hemisphere and is seen by all persons able to view the
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Full Moon. Lunar eclipses can last for hours because the Moon and Earth are moving slowly
in relation to each other, and the shadow cast by the Earth is very large.
A solar eclipse occurs when the Moon comes directly between the Earth and Sun
(New Moon), and blocks the Sun’s rays. The Moon’s path is usually too high or too low for a
solar eclipse to occur most of the time. A solar eclipse always occurs two weeks after or
two weeks before a total lunar eclipse. Solar eclipses last for a matter of minutes and are
visible in a narrow path around the Earth.
Homework Assignment #5
Label the diagram with the correct moon phase. The outer images are how the Moon
appears from Earth…these are the images you should label. There are 8 in all. (You may
need to look at your vocab words or do some extra searching to help guide you)
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Part 3: The Solar System
Galactic Address
Most students know their home address, but do
they know their galactic address? We are but a small spot
on Earth in an immense solar system, galaxy and universe.
We live in the Milky Way Galaxy. Most galaxies belong to
groups called clusters of galaxies. The Milky Way Galaxy
belongs to a cluster called the local group which contains more than 20 galaxies in a great
sphere. There are thousands of other clusters of galaxies that contain over one thousand
galaxies called rich clusters. The closest one is in Virgo (holds 2500 galaxies).
Superclusters are the largest known formations in the universe and we belong to the Virgo
super cluster.
Where are we in the universe? Our home, planet Earth, is part of the solar system
which is in the Milky Way Galaxy. The Milky Way Galaxy is part of a cluster of galaxies.
These clusters make up super clusters, such as the Virgo super cluster. A map is a
representation of a particular area and may be drawn or photographed and labeled from
different points of view. The amount of human made or natural objects seen in satellite
images varies depending on your point of view. The higher the elevation, the less human
made objects we see and the more natural objects that will be visible.
Homework Assignment #6
You are an employee of Google maps. Someone from a distant planet (outside the Virgo
supercluster) asks you for directions to your house. In the space below, provide them
with the directions they need…
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Scale Models of Our Solar System
Models are important to demonstrate size of objects in our solar system. There are
different types of models that are used in the science classroom. Conceptual models are
used to explain something that we cannot directly see. Physical models are a simplified
construction of real objects.We use a model of the Solar System
because it is very large, and models may also be used for things
that are very small, like cells.
Most depictions of the solar system, whether in posters,
videos, or films, give the impression that the distances between
planets are only somewhat larger than the diameters of the planets themselves. To a great
extent, this impression results from the limitations of 2-dimensional or even threedimensional artwork. Thus, in some ways, our natural, human visual sense betrays us when it
comes to making sense of something as outsized as the solar system, not to mention the
Universe.
Homework Assignment #7
Bodes’ Law: In 1766, Johann Titius developed a mathematical relationship between the distances
of the planets from the Sun and it was published in 1772 by Johann Bode. The law states this
relationship between planets can be found by using a series of numbers starting with zero and
jumping to 3 and then doubling the following numbers, Then 4 was added to each number, divided
by 10 and this value represented the AU (Astronomical Unit) from Sun. Find the missing numbers
for Jupiter and Saturn!
Numbers
Add 4
Divide by 10
AU
Planet
0
4
.4
0.39
Mercury
3
7
.7
0.72
Venus
6
10
1.0
1.0
Earth
12
16
1.6
1.6
Mars
24
28
2.8
2.8
48
_____
_____
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Jupiter
_____
_____
_____
_____
Saturn
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Asteroid belt
More Gravity
Remember the two factors that influence gravitational pull: mass and distance.
Since the Sun’s mass is roughly 99% of the mass in the solar system, all objects in the
solar system revolves around our star. But what happens when we travel farther away from
Earth? Even though we are still affected by the Sun’s gravity, we begin to be less
affected by the Earth’s gravity. However, there is nowhere in the universe you can go and
not be affected by gravity…that we know of!!
So How Do Astronauts Float Around in Space?
We have all seen the images and videos of astronauts
floating around in space and it is generally referred to as a
“weightless” or “microgravity” environment. But this
contradicts our previous discussion that gravity never goes to
zero, let alone for astronauts that are only a few hundred
miles from the surface of the Earth. The terms
weightlessness, zero gravity, and microgravity refer to a
sensation of being weightless. By all appearances, gravity has disappeared, but this is not
true. The space shuttle, the space station, and satellites are actually falling towards the
Earth because the Earth’s gravity is pulling them downward just like it would do to any
object that get tossed up into the air. The spacecraft and astronauts are moving forward
while they are also falling downward. Since the Earth is a sphere, the astronauts and the
spacecraft actually fall around the Earth. You would feel the same sensation, for a short
amount of time if you were to ride the Free Fall ride at Six Flags Great Adventure in New
Jersey or if you rode in the Vomit Comet, which is a plane that is used to train astronauts
for this free fall condition. Due to this free fall situation, it appears as if all objects have
no weight, when actually they have not traveled far enough away from the center of the
Earth to experience any significant weight loss. What is really happening is that all of the
objects are falling at the same rate around the Earth. Since things in this free fall
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environment behave like there is no gravity at all, scientists use the terms weightlessness,
zero gravity, and microgravity to describe it even though the gravity is not zero or
“micro”.
How Do Humans React to Space?
Humans may live in space for longer periods of time in
the future. Past missions in space travel have revealed that
this free fall (or microgravity) environment can have
negative effects on the human body. Our bodies have
evolved to handle the Earth’s always-present downward
force of gravity, but when put into a situation, such as in
orbit, where the body feels as if the force of gravity was
turned off, the human body adapts to the new environment.
This is the reason that astronauts must exercise regularly in
space. As scientists study ways to combat gravity related
problems in space, such as bone degeneration, they have also made advances in similar
problems already existing on our planet.
Homework Assignment #8
Think of an Olympic or sports event (running, diving, basketball, soccer, etc.). Now
think of how that event would be played on the Moon (where there is less gravity and
humans can jump higher and throw farther). Write down how you would change the
equipment, rules, goals, etc. so it could be played on the Moon.
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