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All matter and energy, including the earth, the
galaxies, and the contents of intergalactic space,
regarded as a whole.
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A component of our universe made up of gas
and a large number (usually more than a
million) of stars held together by gravity. When
capitalized, Galaxy refers to our own Milky
Way Galaxy.
Three types of galaxies:
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Elliptical
Spiral
Irregular
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Have a
round
Oval
Shape
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Pinwheel
Shape
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No
predictable
shape
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Elliptical
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Are huge
Contain
stars, gas,
& dust
Are held
together
by gravity
A halo is
present
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Spiral
Are huge
Contain
stars, gas,
& dust
Are held
together
by
gravity
A halo is
present

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Irregular
Are huge
Contain
stars, gas,
& dust
Are held
together
by gravity
A halo is
present
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Elliptical

Pinwheel
shape
Bulge & a
thin disk
Rich in
gas & dust
Young &
old stars
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Spiral
Round to
oval
shape
Bulge, but
no disk
Small
amount
of cool
gas &
dust
Mainly
old stars
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Irregular
No
predictable
shape
May show
signs of a
disk &/or a
bulge
Usually rich
in gas & dust
Young & old
stars
Our place in the universe. This figure illustrates our cosmic address.
The Earth is one of the nine planets in our solar systems, our solar
system is one among 200 billion star systems in the Milky Way
Galaxy; the Milky Way is one of the two largest of about 30 galaxies
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Ask an Astrophysicist
Size: The disk of the Milky Way galaxy is about
100,000 light years in diameter (one light year
is about 9.5 x 1015 meters), but only about 1000
light years thick.
Our Galaxy contains about 200 billion stars.
Most of the stars are located in the disk of our
galaxy, which is the site of most of the star
formation because it contains lots of gas and
dust.
Solar System's orbit within Milky Way
Galaxy. The sun is ONE of the estimated
200 billion stars in this galaxy.
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Our solar system
consists of:
the sun, eight planets,
moons, many dwarf
planets (or plutoids),
an asteroid belt,
comets, meteors, and
others.
The sun is the center
of our solar system;
the planets, their
moons, a belt of
asteroids, comets, and
other rocks and gas
orbit the sun.
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A Globule of Gas:
Our solar system formed about
4.6 billion years ago, from an enormous cloud
of dust and gas, a nebula.
The Sun, like other stars, was formed in a
nebula, an interstellar cloud of dust and gas
(mostly hydrogen).
These stellar nurseries are abundant in the
arms of spiral galaxies (like our galaxy, the
Milky Way).
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Later, the Sun stabilizes and becomes a yellow
dwarf, a main sequence star which will remain
in this state for about 10 billion years. After
that, the hydrogen fuel is depleted and the Sun
begins to die.
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Inner- Terrestrial (Land)
Mercury, Venus, Earth,
& Mars
Closer to the Sun
Are rocky & have
craters
Atmosphere: MercuryN/A; other planets have
CO2 in common. Earth
only one w/O2
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http://lasp.colorado.edu/educatio 
n/outerplanets/solsys_planets.ph
p
Outer- Gas Giants
Jupiter, Saturn,
Uranus, Neptune, &
Pluto (a dwarf
planet)
Farther from the Sun
(cooler)
Farther apart from
one another
Are made of gas
Atmosphere: mostly
Helium & Hydrogen
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Jupiter: Strongest
gravitational attraction
Although Saturn, Uranus,
and Neptune are also very
massive planets, their
gravitational forces are about
the same as Earth.
This is because the
gravitational force a planet
exerts upon an object at the
planet's surface is
proportional to its mass and
the planet's radius squared.
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Inner- Terrestrial
Mercury, Venus, Earth,
& Mars
Few moons
Mercury & Venus no
moons
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Outer- Gas Giants
Jupiter, Saturn,
Uranus, Neptune, &
Pluto (a dwarf
planet)
Many moons
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Jovian Planets collapsed,
smaller particles in the
surrounding disk formed
into some of the moons
that now orbit the individual
outer planets. This makes
sense, since the outer
planets all have many
moons and rings.
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Inner- Terrestrial
Mercury, Venus, Earth,
& Mars
No rings
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Outer- Gas Giants
Jupiter, Saturn,
Uranus, Neptune, &
Pluto (a dwarf
planet)
Rings

The rings are thin discs of
dust and rocks possibly
caused by moons being
broken up or not being
completely formed while
orbiting the planet.
An asteroid is a bit of rock.
 "left overs" after the Sun
and all the planets were
formed.
Most of the asteroids in our solar system can be
found orbiting the Sun between the orbits of Mars
and Jupiter.
This area is sometimes called the "asteroid belt“.
Think about it this way: the asteroid belt is a big
highway in a circle around the Sun. Think about
the asteroids as cars on the highway.
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The asteroid belt lies
between the orbits of Mars &
Jupiter.
Jupiter is the most massive
body in our solar system after
the Sun, and it therefore exerts a substantial
amount of gravity on the objects around it.
The competing gravitational influence of Jupiter
and the Sun did not allow the bits and pieces of
the asteroid belt to accrete into a larger planet.
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Probably a rocky planet similar to Mars, except
smaller. All the asteroids combined are not as
much mass as Mars is.
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A meteor is a bright streak of light that appears
briefly in the sky.
Observers often call meteors shooting stars or
falling stars because they look like stars falling
from the sky.
A meteor appears when a particle or chunk of
metallic or stony matter called a meteoroid
enters the earth's atmosphere from outer space.
Why was early Earth hit with so many meteors
than the current Earth?
 They delivered enough carbon dioxide and
water vapor to turn the atmosphere of planets
into warmer and wetter environments that
were more habitable for life.
 Also, increased
Earths size and
caused thermal
energy.
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(1) the Earth has the right conditions (such as
carbon and a temperature that allows liquid
water)
It is at a perfect distance from the Sun; not too
hot, not too cold. A temperate climate.
Earth is 94 million miles (150 million km) from
the Sun.
Ideal gravity which makes moving about easy
without the difficulty of heavy gravity and low
gravity. Earth's diameter is 7,926 miles (12,756
km).
Stars are born in
nebulae. Huge clouds
of dust and gas
collapse under
gravitational forces,
forming protostars.
These young stars
undergo further
collapse, forming
main
sequence stars.
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Stars expand as they
grow old.
-As the core runs out
of hydrogen & then
helium, the core
contacts & the outer
layers expand, cool, &
become less bright.
This is a red giant
or a red super giant
(depending on the initial mass of
the star). It will eventually collapse
and explode.
- Its fate is determined by the
original mass of the star; it will
become either a black dwarf,
neutron star, or black hole.
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H-R
Diagram
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- O and B
stars are
uncomm
on but
very
bright
- M stars
are
common
but
dim..
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The Hertzsprung -Russell (H-R) Diagram is a
graph that plots stars color (spectral type or
surface temperature) vs. its luminosity
(intrinsic brightness or absolute magnitude).
On it, astronomers plot stars' color,
temperature, luminosity, spectral type, and
evolutionary stage.
This diagram shows that there are 3 very
different types of stars:
 Most stars, including the sun, are "main
sequence stars," fueled by nuclear fusion
converting hydrogen into helium.
 For these stars, the hotter they are, the brighter.
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As stars begin to die, they become giants and
supergiants (above the main sequence).
 These stars have depleted their hydrogen
supply and are very old.
 The core contracts as the outer layers expand.
These stars will eventually explode (becoming a
planetary nebula or supernova, depending on their
mass) and then become
white dwarfs, neutron stars, or
black holes (again
depending on their mass).
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Smaller stars (like our Sun) eventually become
faint white dwarfs (hot, white, dim stars) that
are below the main sequence.
These hot, shrinking stars have depleted their
nuclear fuels and will eventually become cold,
dark, black dwarfs.
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is the apparent change in the position of a star
that is caused only by the motion of the Earth
as it orbits the Sun.
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Earth only planet currently suitable for Ag
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As of the year 2000, about 37 percent of Earth's land
area was agricultural land.
Characterizes land's suitability for agriculture based
on physical parameters like climate, soil, and
topography.
Unsuitable land surfaces for growing is subject to
some soil, terrain, and/or climate limitations.
How is animal breeding cycles
impacted by the rotation of Earth?
 Sheep are seasonal breeders, with the majority
being short-day breeders that cycle in the fall
and lamb in the spring of the year.
 However, some breeds of sheep will cycle in
the spring and have lambs in the fall.
 Through the eye of the sheep, its brain
perceives day length and sends appropriate
signals (hormones) to the reproductive system
to begin the breeding season.
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