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‘The Universe’
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Many discoveries are credited to scientists
from Greece
1. Geocentric Model
◦ People once thought Earth was the center of
the Universe
◦ They thought the moon, Sun, and other
planets orbited Earth
Geocentric Model:
In this 1st model, the Sun
revolves around the EARTH.
*Scientists in the 16th and 17th centuries made
observations that made this model difficult to
accept – it did not make sense based on what
they were seeing.
So they came up with:
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2. Heliocentric Model
◦ People changed their thinking to the Sun
being the center of the solar system instead
of the Earth
◦ So, they finally believed that the planets and
moons orbit around the Sun
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Heliocentric Model
In this model, the earth revolves
around the SUN.
Objects in space are in motion –
they move!:
Spinning in place; like a dradle
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A. Rotation
◦ Spin of a body on its imaginary axis
◦ On Earth:
 Rotates once every 24 hours
 Causes day and night
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B. Revolution
◦ Movement/orbit of a body around a larger
one
 Earth revolves around the Sun and the
moon revolves around Earth
 Earth revolves around the Sun once a
year (every 365 days)
◦ Orbit is elliptical (oval-shaped) so
the distance from the sun changes
1. Perihelion – Earth is closest
to Sun (1/3)
2. Aphelion – Earth is farthest
from Sun (7/4)
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C. Force of Gravity
◦ Gravity = the force of attraction between 2
objects
◦ Depends on the mass of each object and
the distance between them
◦ Greater mass = greater force of gravity
◦ Less of a distance between objects = less
force of gravity
◦ Gravity holds planets and other space
objects in their orbits
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2. Measuring Distance in Space
A. Light year – unit of measure for the
distance between objects in space
◦ Distance light travels in 1 year
◦ Light travels about 5.8 million miles a year
◦ Travels 186,000 miles per second
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A. The Moon
◦ Earth’s only natural satellite
◦ May have formed when a body the
size of Mars struck Earth and
resulted in a part of Earth breaking
off
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Characteristics:
◦ Rotates once on axis every 29 days
◦ Revolves once around Earth every 29 days
– so only see 1 side of moon
◦ No atmosphere or water
◦ Many craters
◦ 1/6 the gravity of Earth
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Phases of the Moon – during its trip around
Earth, the lighted area of the moon seems
to change shape
◦ Moon reflects the light of the Sun
◦ Starts with new moon
 Moon and sun are on the same side of
Earth
 Dark side faces the Earth – cannot see
moon
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Eclipses:
◦ Occur when 1 body passes through
the shadow of another.
◦ Types:
1. Lunar Eclipse – Earth is
between moon and Sun
2. Solar Eclipse – Moon is between
Earth and Sun
Can you see the
small dot in the
middle of the circle?
That is the moon
blocking out the
SUN.
Notice that the MOON is being
blocked out.
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Tides:
◦ Rise and fall of the ocean that occurs twice
a day
◦ Cause of tides = gravitational pull from
moon
◦ Pulls on one side of Earth, then the other
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1. Facts:
◦ Contains planets, moons, stars, comets,
asteroids, etc.
◦ About 4.6 billion years old
◦ Big Bang Theory – Theory that a huge
explosion created the universe about 20
billion years ago
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2. Within our Solar System:
A. Planets:
 2 groups:
 Inner
 Rocky (terrestrial) planets – mostly
rock with little gas (smaller)
 Mercury, Venus, Earth, Mars
 Outer
 Gas giants – large planets – small
liquid/rock core surrounded by
mostly gas
 Jupiter, Saturn, Uranus, Neptune
 Dwarf Planets
 Too small to be an actual planet
 Ceres – in asteroid belt
 Pluto and Eris – orbit beyond Neptune
◦ Surface temp on planet depends on its
distance from the sun
 Mars and Venus are the hottest
 Venus is the hottest planet – has a very
dense atmosphere with lot of carbon
dioxide (greenhouse gas that traps sun’s
heat)
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Planets revolve around sun because sun’s
gravity is so great
Planet
Characteristics
Mercury
1. No moons
2. Closest planet to
the sun
Venus
1. No moons
2. Hottest planet
3. Brightest planet in
our sky
Planet
Characteristics
Earth
1. Has life because of
liquid water, proper
temp., and atmosphere
with oxygen
2. Has seasons
3. 1 moon
Mars
1. Called ‘Red Planet’
2. Has largest volcano in
solar system
Planet
Characteristics
Jupiter
1. Largest planet
2. Most moons
3. Has ‘Great Red Spot’
Saturn
1. Known for its rings
2. 2nd largest
Planet
Characteristics
Uranus
1. Rotates lying on its
side
2. Blue-green in color
from methane gas
Neptune
1. Has ‘Great Dark Spot’ –
hurricane-like storm
2. Has strongest winds
3. Bright blue color due
to methane gas
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Seasons on Earth - due to Earth’s tilt
at 23 ½ degrees
◦ Earth is closest to the sun in the
winter and farthest from the sun in
the summer
◦ The tilt is what determines how cold
or hot it is
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1. Equinoxes
 When there is exactly 12 hours of
daylight
 Vernal (spring) equinox- – around 3/21
 Autumnal equinox (fall) – around 9/22
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2. Solstices – Depends on the length of the
sun’s path through sky
 Summer = longest day of year (greatest
amount of daylight)
 Winter = shortest day of year (shortest
amount of daylight)
 1.
Asteroids
◦ Irregularly shaped rocky and
metallic objects
◦ Orbit the sun - mostly found in
asteroid belt between Mars and
Jupiter
◦ Range in size from a pebble to
600 miles across
◦ Idea that 65 million years ago an
asteroid struck Yucatan
Peninsula in Mexico that led to
mass extinction (dinosaurs)
 2.
Meteoroids
◦ Asteroids that have entered
Earth’s atmosphere
3. Meteors
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Small, solid particles from space –
enter Earth’s atmosphere
Burn up due to friction = ‘shooting
stars’
4. Meteorites
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Meteors that hit the ground

The crater is 1.2
kilometers in diameter
and 200 meters deep.
It formed
approximately 49,000
years ago when an iron
meteorite that was
roughly the size of a
school bus struck the
Arizona desert east of
what is now Flagstaff.
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5. Comets
Called ‘dirty snowballs’
Made of ice, frozen gas, dust
Orbit the sun
◦ When they get close to the sun, they vaporize and
a tail is produced
◦ Example – Halley’s Comet – orbits the sun once
every 75 years- next appearance 2061
 6.
Satellites and probes
◦ Example – US owned Hubble
Space Telescope – orbits Earth –
has made numerous discoveries
http://hubblesite.org/
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C. Galaxies
◦ Solar systems are found in galaxies
◦ Define Galaxy  Huge body of stars and other
matter in space
 There are billions of stars in each
galaxy
 Types
of Galaxies
◦ 1. Spiral galaxy – spiral shaped,
has arms – made of old and
young stars
 2.
Elliptical – most common
shape, smaller than spiral, old
stars, oval-shaped
Ex – Andromeda Galaxy
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Irregular – least common, no
definite shape, made of young
stars
3.

Draw the shape of each type of galaxy:
Spiral
Elliptical
Irregular
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We live in the Milky Way Galaxy
◦ Early astronomers looked into sky – they
observed a dim band of light across sky, so they
called it the Milky Way for its faint white color
◦ About 100,000 light years wide
◦ Milky Way is a spiral galaxy - our solar system is
in 1 arm
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Local Group ◦ Closest 30 galaxies to us
◦ Example – Andromodea –
 One of our closest neighbors
 It’s so far it takes light from there 2 million
years to reach us.
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D. Stars
1. Large bodies of gas that create
energy
2.
Temperature
 Can be estimated by the color they shine and
their brightness
 Violet stars are very hot (short, fast
wavelength of light)
 Red stars are cooler (longer, slower
wavelength of light)
 Yellow stars (like the sun) are in between
 Most common elements in stars are H and He
3. The Sun
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Facts
 Average-sized star that is the closest
star to Earth
 Core is 15 million degrees Celsius
◦ Mass is 300,000 times Earth’s mass, so its
huge gravity keeps planets in orbit around
it
◦ Produces energy through nuclear fusion –
hydrogen is changed into helium
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Features
◦ Sunspots
 Dark spots on surface of sun
 Temporary storms that are cooler than rest of
surface
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Movement of sunspots proves that the sun rotates
◦ Solar flares
 Brief explosions near sunspots
 Release tons of energy
 Can result in auroras
 Called northern and southern lights
 Makes atmosphere glow beautiful
colors
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4. Nebula
◦ Areas of gas and dust – glow different
colors
◦ May be where stars are born
Crab Nebula
Helix Nebula
5. Star evolution (how they change over
time)
◦ 1. Birth – born in dark, cool clouds rich in
gas and dust (nebula) maybe due to a
shockwave
◦ 2. Protostar – large red object – not hot
enough yet for nuclear fusion, so not yet a
star
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3. Main-sequence stage – main part of a
star’s life – the sun is in this stage – lifespan
of sun is about 10 billion yers – it’s about ½
way through life, so as about 5 billion more
years to go
4. Red Giant stage – all of the hydrogen is
gone in the core, so the star expands, the
surface cools, and it turns red
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5. Burn-out and death - what happens to
the star depends on its size – it could turn
into a neutron star or black hole
a. Black hole
 A crushed in star - so dense they
suck in nearby objects , they’re dark,
and they give off x-rays