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Astronomy
Earth’s Motions and the Universe
Write down anything in yellow!
The Earth
What is the shape of
the Earth?
Oblate Spheroid
• Where on Earth’s
surface would you
experience the most
gravitational pull?
The Poles
• Where would be the
least gravitational
pull?
The Equator
•
Earth’s Motions
 Rotation-
The spinning of an object,
such as a planet, moon, or star, on an
imaginary axis
 Earth’s Rotation Animation
 Rotation Facts:
-Rotates 360° in 24 hours
-360°/24 hours = 15°/hr
-Rotates from west to east,
counterclockwise
15°/hr
Because the Earth rotates 15°/hr, we have
time zones
 There are 24 lines of longitude on Earth’s
surface, and 24 hours in one day.
 Every time you cross one longitude line
you have changed time by one hour.
As you go east, your time will increase! As
you go west, your time becomes less!

Time Zones and Longitude
Proof of Rotation
 Foucault’s
Pendulum
 Coriolis Effect
 Star Trails
 Apparent Motion of the Stars in the
Night Sky
 Apparent Motion of the Sun
 Day and Night
Foucault’s Pendulum

When a Foucault
Pendulum swings
freely, its path
appears to change in
a predictable way.
It is not actually
changing- it is
swinging in a fixed
direction, while the
Earth rotates under
the pendulum
Coriolis Effect
•
•
The tendency of all
particles of matter
moving at Earth’s
surface to be
deflected or curved
from a straight line.
Is caused by Earth’s
rotation
Curves to the right in
the northern
hemisphere!
Star Trails- Where is Polaris?
Apparent Motion of the Stars
Most celestial objects appear to move
across the sky but are not actually moving.
 Because of Earth’s rotation, stars appear
to rise at night, move across the southern
sky, then set in the west before dawn.
 Some of the stars near Polaris appear to
move in a complete circle in 24 hours (star
trails). All the motion occurs at a constant
rate of 15°/hr or 360° in 24 hours.

Apparent Motion of Stars
North
East
South
West
Apparent Motion of the Sun

Is the Sun really moving across the sky
during the day?
NO!!!!
Just as with other stars, the Sun is a star
that appears to move across the sky,
rising in the east, moving across the
southern sky, then setting in the west.
Apparent Path of the Sun in NYS
Polaris
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The Sun is always found on the southern side of
the celestial sphere.
In the summer (June 21st) and spring (March
21st), the sun rises north of east and sets north
of west.
In the winter (December 21st) and fall
(September 21st), the sun rises south of east
and sets south of west.
Apparent Path of Sun in NYS
Where does the sun rise on March 21st
and September 21st?
Rises directly in the east and sets directly in
the west.
 What is special about these two dates?
They are the equinoxes!
12 hours of daylight, 12 hours of darkness
for every location in the world.

Apparent Path of the Sun in NYS
Will the sun ever be directly overhead in
NYS?
NO!!
The highest the sun will ever get in the sky
will be on June 21st (the summer solstice)
at solar noon, and it will reach an altitude
of 71° at that time!

Shadows
Looking South
12 PM
10 AM
8 AM
6 AM
2 PM
4 PM
6 PM
Earth’s Second Motion
Revolution- the orbiting of a celestial body
around another celestial body
 Earth’s Revolution Around the Sun
Animation
 Facts about revolution:

Average orbital velocity: 66,629 mph
 Orbital Circumference: 574,380,400 miles
 Length of period of revolution: 365.24 days

Rate of Revolution
How long does it take the Earth to move around
the Sun?
approximately 365 days
How many degrees does the Earth move around
the sun?
360°
What is the rate of revolution?
360º = ~1°/day
365 days
Results and Proof of Revolution
Nighttime constellations (a group of stars
that form an imaginary pattern of
mythological origin) change in a yearly
cycle.
Constellation Changes Animation
1)
2)
Yearly cycle of the seasons.
Seasons of the Year
Causes of the Seasons
1)
2)
3)
Earth’s revolution around the sun
Earth’s axis is tilted 23 1/2°
The way Earth is tilted does not change
throughout the year (parallelism of axis)
Fall
Summer
Winter
Spring
Amount of Insolation
Arctic Circle
Attica
Tropic of Cancer
Equator
Tropic of Capricorn
Antarctic Circle
When Do Seasons Begin?
What season is shown in the picture?
Winter
How do we know?
The sun is directly overhead at the Tropic of
Capricorn.
What is the date in the picture?
December 21st
Solstices
Solstice- sun stops
 The solstices occur twice a year
1) June 21st (longest day of the year)
2) December 21st (shortest day of the year)
On June 21st, the sun is directly overhead at
23 1/2°N (Tropic of Cancer). In Attica we receive
15 hours of daylight and 9 hours of darkness.
On December 21st the sun is directly overhead at
23 1/2°S (Tropic of Capricorn). In Attica we
receive 15 hours of darkness and 9 hours of
daylight.

The North Pole on the Solstices
December 21st- 24
Hours of Darkness
June 21st- 24 Hours
of Daylight
The South Pole is the opposite! 12/21- 24 hrs daylight, 6/21-24 hours
darkness
Equinoxes
Equinox- equal night/equal day
 12 hours of daylight and 12 hours of
darkness for every place in the world
 This occurs on March 21st (Vernal
Equinox) and September 21st (Autumnal
Equinox)
 The Vernal Equinox marks the beginning
of Spring
 Autumnal Equinox marks the beginning of
Fall

Rotation/Equinox Diagram
Shade in the area that is in darkness.
At what latitude is the sun directly overhead in this picture?
6 AM
8 AM
12 PM
12 AM
6 PM
Write down the time at the following longitudes: 0°, 90°E, 180°, 90°W,
and 120 °E.
Changes Through the Year
This diagram was drawn to show the dates of
March 21st and September 21st. If it was drawn
to show December 21st, what would be different
at the North Pole?
The North Pole would be completely shaded to
represent 24 hours of darkness.
If it was drawn to show June 21st, what would be
different at the North Pole?
The North Pole would not be shaded at all to
represent 24 hours of daylight.
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More On Revolution…
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1)
2)
3)
Newton’s Laws of Gravity and Inertia
All objects possess gravity.
The mass of an object determines the amount
of gravitational force that object possesses.
The greater the mass, the greater the
gravitational force.
The gravitational force between two objects
changes as the distance between them
changes.
As distance increases, gravity decreases!
Why doesn’t the Earth get pulled right into the sun if the
gravitational pull from the sun is so much higher than the
gravitational pull of the Earth?
It is because of inertia!
 An object in motion will stay in motion
unless acted upon by some outside force.
 The Earth is trying to travel in a straight
line out into space, but because of the pull
of gravity from the sun, it stays in a stable
orbit.
Gravity + Inertia = Stable Orbit

Gravity and Inertia
GRAVITY
INERTIA
Kepler’s Laws
As the distance
between foci
increases,
eccentricity
increases!!!!
The orbit of a planet is an ellipse with the
sun at one focus.
Formula for eccentricity of an ellipse:
distance between foci
length of major axis
1)
d
L
Law 2

During its orbit a planet’s orbital velocity
changes. It is traveling fastest when it is closest
to the sun, slowest when it is farthest from the
sun.
Perihelion
Aphelion
Animation
Law 3
The farther a planet is from the sun, the
greater the period of revolution (time it
takes to complete an orbit).
 The farther a planet is from the sun, the
greater the length of its orbit.
 The farther a planet is from the sun, the
slower its orbital speed.
As distance from the sun decreases, orbital
speed increases!

Outside of Earth’s Atmosphere
T
H
E
M
O
O
N
Formation of the Moon
Moon Facts
The moon follows the daily east to west
motion of the stars, but rises 50 minutes
later each day and shifts 13° eastward
each day compared to the background
field of stars.
 The revolution of the moon around the
Earth follows an elliptical shape and has a
period of 27.32 days.
 The revolution of the moon is tilted about
5° from Earth’s orbit. This explains why
we do not see eclipses every month.

Moon Facts
The moon rotates in a period of 27.32
days.
 Because the moon’s rotation and
revolution periods are equal, we only ever
see one side of the moon.
 We see moon phases because the moon
revolves around the Earth.
 One moon phase cycle takes 29.5 days to
complete.

Moon Phases

There are 8 main moon phases, being
1) New Moon
5) Full Moon
2) Waxing Crescent
6) Waning Gibbous
3) 1st Quarter
7) 3rd Quarter
4) Waxing Gibbous
8) Waning Crescent
Pictures of the Phases
Phase Animation
Eclipses
The two types of eclipses are solar and
lunar.
 We do not see eclipses every month!
 Total lunar eclipses occur when the moon
passes into the darkest part of Earth’s
shadow (the umbra).
 Total solar eclipses occur when the
darkest part of the moon’s shadow (also
called the umbra) is cast onto Earth’s
surface.

Solar Eclipses
Solar Eclipse Animations
Solar Eclipse Diagram
Lunar Eclipse Diagram
Lunar Eclipse Animations
What the moon would look like.
Tides
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Tides occur because of the gravitational
attraction between the moon and the Earth.
Water in the oceans attracted by the Moon’s
gravity flows into a bulge of water on the side of
Earth facing the Moon. (It also pulls the Earth’s
bedrock but isn’t as noticeable because it is not
as fluid as the water. The bedrock may only rise
one inch.)
A bulge of water also forms on Earth’s far side
because the moon pulls on the Earth’s center
more strongly than on Earth’s far side. This
attracts the Earth away from the oceans on the
far side, and the water flows into this space,
creating a bulge.
Spring Tides
Spring tides occur when the moon, Earth, and
sun are all in line with each other.
 What moon phases would result in a spring tide?
Full Moon and New Moon
The sun and the moon pull in the same direction,
therefore their tidal forces combine and tidal
bulges on Earth are larger.
Creates very high high tides and very low low
tides!

Neap Tides
Neap Tides occur when the moon, sun, and
Earth are at a right angle.
 What moon phases would result in a neap tide?
1st Quarter and 3rd Quarter
The gravitational pull of the moon and the Sun are
now working against each other.
Creates low high tides and high low tides.

Tides Animation
Earth in the Universe
Meteor Crater, Arizona
The Earth is a
celestial object (any
object outside or
above Earth’s
atmosphere).
 Other examples of
celestial objects:
Meteors, comets,
asteroids, moons,
stars

Meteors
Hale-Bopp Comet
Observe an animation of a
comet's passage through
the solar system.
The Big Bang Theory
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States that all matter and energy started out
concentrated in a small area and, after a
gigantic explosion, matter began to organize into
subatomic particles and atoms
Most of the early atoms were hydrogen and
helium
Within a few hundred million to a billion years,
atoms became organized into celestial bodies
While all of this was happening, the universe
was expanding
Evidence of the Big Bang
Cosmic Background Radiation
The sound of the explosion was so loud that
we can still hear it in space!
The Doppler Effect (Shifting of Wavelengths)
The Blue Shift is seen when Earth and another
object are moving closer together (waves are
bunched together)
The Red Shift is seen when Earth and celestial
objects are moving farther apart (waves are
spread out)
The Red Shift

The collective light
from the stars in all
galaxies, except for a
few close to Earth, is
shifted to the red end
of the spectrum,
indicating the
universe is expanding
in all directions
Dark Matter Video
Structure of the Universe
The Universe is the largest, holding mostly
galaxies. Within the galaxies there are
stars. Within the stars, there are solar
systems. Within solar systems there are
planets.
what we can see in the universe
Galaxies
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A galaxy is a
collection of billions of
stars and various
amounts of gas and
dust held together by
gravity
Our solar system is
part of a spiralshaped galaxy called
the Milky Way
Milky Way- Side View
Our Neighbor- Andromeda
Stars
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A star is a large ball
of gas held together
by gravity that
produces tremendous
amounts of energy
and shines.
Energy in stars is
produced by nuclear
fusion
Our star is the Sun
Luminosity
Luminosity measures how bright it would
be in relation to the sun if all stars were
the same distance from an observer.
 Larger stars have higher luminosities
 Apparent Magnitude- how bright the star
appears to an observer on Earth
 Absolute Magnitude- the apparent size the
star would have if placed at a distance of
32.6 light years from the sun

Absolute Magnitude
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Term used to express the luminosity of stars if
they were seen from the same distance
Some stars that are smaller look brighter only
because they are closer to us than other stars
that are actually much more luminous.
If all stars were placed at the same distance
from the sun, their true brightness could be
compared
Types of Stars
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Main Sequence Stars- Average Stars
Giant Stars (red, orange and yellow)- are rare
but are commonly seen in the night sky because
of their large size
Super Giants- blue super giants are the biggest,
brightest stars
White Dwarfs- small and low in luminosity
Black Dwarfs- when a white dwarf cools and no
longer emits much electromagnetic energy
Life Cycle of Stars
Black Holes

Are created in a supernova

Birth of a Black Hole
Solar Systems
A solar system is a star and all the objects
that orbit it.
 Our solar system contains the sun, 8
planets, asteroids, moons, comets, and
meteoroids.
Travel through our solar system

Planet Characteristics
Terrestrial Planets- close to the sun and
solid (Mercury, Venus, Earth, and Mars)
 Jovian Planets- far from the sun and made
of gas (Jupiter, Saturn, Uranus, Neptune)
 In between the Terrestrial Planets and the
Jovian Planets lies the asteroid belt
 This belt is located between Mars and
Jupiter
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