Stars

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Stars Galaxies
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Metric Review
SI Base Unit for Length
meter (m)
1000m 1km
1mile 1.6km
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Distance in Space
In space, distances are much larger than anything
we deal with on earth.
example the distance from Earth to the Sun is
93,000,000miles
Scientists have designated this distance 1
astronomical unit (AU).
1AU 93,000,000mi 149,668,992km
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Distance in Space
Even AU is a very small distance in space.
Normally, distance is measured in
Light Years
- the distance light is able to travel in one
year.
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the Speed of Light
light travels at a rate of 300,000km/s
or 300,000,000m/s
or 186,000mi/s
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One Light Year (ly) is the distance light can
travel in a years time
1ly 9,460,000,000,000km
or 6,000,000,000miles
or 63,239AU
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The closest star in our galaxy to the Sun,
Proxima Centauri, is 4.3ly away!
or 271,930AU
or 25,277,549,200,800 miles
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An even larger measurement of space distance is a
parsec (pc)
1pc 3.26ly
or 206,161AU
or 19,163,909,394,100 miles
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The distance from Earth to the center of our
Milky Way galaxy is 8,000 parsecs.
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Light
- energy that moves as a wave.
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Speed of Light

• all light travels at the same speed
• 300,000,000m/s

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Understanding Waves
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Understanding Waves
wavelength
- the distance between two crests
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Understanding Waves
frequency
- the number of crests
that pass a given point in one second.
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Which set of waves has the highest frequency?
wavelength?
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Frequency and wavelength are inversely related
- as wavelength increases, frequency decreases
- as wavelength decreases, frequency increases
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Light Energy
high energy light
- short wavelengths, high frequencies
low energy light
- long wavelengths, low frequencies
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Which set of waves has the highest energy?
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Light energy exists at every wavelength and
frequency this range of values is called the
Electromagnetic
Spectrum
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Visible Light
- we can only see a small fraction of all the
light frequencies that exist
700nm
400nm
nm nanometer 0.000000001m
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Less Energetic Light
(wavelengths longer than visible light)
Infrared
wavelengths 700nm to 1mm
- invisible, but felt as heat
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Less Energetic Light
(wavelengths longer than visible light)
Microwaves
wavelengths 1mm to 10cm
- used to cook food and for communication
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Less Energetic Light
(wavelengths longer than visible light)
Radio waves
wavelengths 10cm to 100km
- used for communication
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More Energetic Light
(wavelengths shorter than visible light)
Ultraviolet
wavelengths 400nm to 10nm
- emitted by the sun, harmful to tissue
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More Energetic Light
(wavelengths shorter than visible light)
X rays
wavelengths 10nm to 0.01nm
- used for medical diagnosis, emitted by objects
in space
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More Energetic Light
(wavelengths shorter than visible light)
Gamma rays
wavelengths 0.001nm to 0.000001nm
- emitted by objects in space and nuclear
reactions highly dangerous
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Light Review
Does light with longer or shorter wavelengths
have more energy?
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Light Review
Does light with higher or lower frequencies have
more energy?
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Light Review
700nm
400nm
What color of light has the most energy? the
least?
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the Doppler Effect
What happens to the sound of a train or car as it
approaches you? as it passes you and keeps going?
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the Doppler Effect
As a train approaches, its sound waves are
bunched up ahead of it. What does this do to
the wavelength?
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the Doppler Effect
As a train moves away, its sound waves are
stretch out behind it. What does this do to
the wavelength?
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the Doppler Effect

• The same is true for light
• as light waves approach, their wavelengths are
  shorter
• as they move away, their wavelengths are longer

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the Red Shift

• light moving away has longer wavelengths
• these wavelengths are lower energy or shifted
  toward the red end of the spectrum

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the Blue Shift

• light traveling toward Earth has shorter
  wavelengths
• these wavelengths are higher energy or shifted
  toward the blue end of the spectrum

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As astronomers began to study other galaxies,
they began to notice that the light from all of
them was shifted toward red. What does this mean?
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Scientists concluded that the universe is
expanding all galaxies are moving apart. This
led them to the
BIG BANG THEORY
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The Story of the
BIG BANG THEORY
The universe began 15-20 billion years ago
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All of the matter in the universe was squished
into one body as small as an egg
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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The intense heat and pressure caused the matter
to explode outward
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With nothing to stop it, matter and energy shot
in all directions
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With nothing to stop it, matter and energy shot
in all directions
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With nothing to stop it, matter and energy shot
in all directions
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With nothing to stop it, matter and energy shot
in all directions
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With nothing to stop it, matter and energy shot
in all directions
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With nothing to stop it, matter and energy shot
in all directions
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With nothing to stop it, matter and energy shot
in all directions
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With nothing to stop it, matter and energy shot
in all directions
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Matter would have spread evenly throughout the
entire universe, but
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Gravity caused it to begin forming clumps
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INTERMISSION
- the force of attraction between all objects in
the universe
gravity
- the more mass an object has, the larger its
gravitational attraction
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back to our story...
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gigantic clumps of matter eventually formed into
galaxies
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smaller clumps within these large clumps formed
stars and planets
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even as galaxies form and exist, they are
continuing to race away from one another.
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What about the universe today?
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Possibility 1
we live in an open universe
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an open universe
Galaxies will continue to race outward until
they lose all their energy.
Billions of years from now, the universe will
become cold and dark.
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Possibility 2
we live in a closed universe
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a closed universe
Gravitational attraction will one day slow down
the galaxies and then cause them to start moving
back together.
Billions of years from now, all the matter will
be pressed together again, and there could be
another Big Bang.
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- most scientists think our universe is a Closed
Universe and believe that it bangs and then
contracts back onto itself over and over.
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the end...
for now
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Supporting the Theory...
1. red shift
- we know from observing light that galaxies are
moving apart.
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Supporting the Theory...
2. background radiation
- if energy spread evenly during the Big Bang,
then there should be about the same amount
everywhere scientists have observed this
consistent background energy all over the
universe.
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Supporting the Theory...
3. quasars
- the most distant objects we can see are 12
billion light years away
- that means the light of these star-like
bodies is 12 billion years old when we see it!
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Supporting the Theory...
3. quasars
- they are too small to be galaxies, but they
have 100 times more energy than any galaxy
- some scientists think they are pre galaxies
that existed soon after the Big Bang
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Star light, star bright...
Things we can learn from starlight
- star size
- what stars are made of
- temperature of stars
- brightness of stars
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Star
Medium Star(the Sun)
Size
Neutron Star
Giant Star
White Dwarf Star
Supergiant Star
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Star Size
Medium Stars
- the sun and stars 10 times larger or smaller
than it
- most of the stars in the universe
- the suns diameter is 865,000miles or
109 times bigger than Earth!
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Star Size
Giant Stars
- 10 to 100 times larger than the sun
Supergiant Stars
- up to 1000 times larger than sun!
- if it were our sun, it would reach past Mars!
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Star Size
White Dwarf Stars
- smaller across than the continent of Asia
Neutron Stars
- about 16 kilometers (or 10miles) across!
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question
If you hold a bright spotlight and a dim
flashlight next to each other, which appears
brighter?
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question
If a dim flashlight is shining right next to you,
and a bright spotlight is ½ mile away, which one
appears brighter?
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The brightness of stars that we can see from
Earth is called
Apparent Brightness
- depends on the stars size, temperature, and
distance from Earth.
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Scientists can calculate a stars
Absolute Brightness
- the brightness stars would have if they were
all the same distance from Earth.
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Some stars change brightness. These are called
Variable Stars

• ones that also change size are called pulsating
  variables.example Polaris (the North Star)
  changes with a 4 day cycle

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Composition of Stars
(what stars are made of)
- all elements give off particular colors of
light when burning in a flame.
- astronomers separate and study these colors
with a spectroscope
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Composition of Stars
(what stars are made of)
Examplesodium looks yellow burning in a flame
- with a spectroscope, we can see that sodium is
giving off two lines of yellow
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Composition of Stars
(what stars are made of)
Sodium Example
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Composition of Stars
(what stars are made of)
- all elements give off a unique set of lines
when seen through a spectroscope like a
fingerprint
- by studying the lines of starlight, we can tell
what elements are burning in the star
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Composition of Stars
(what stars are made of)

• the most common element in stars is hydrogen
  makes up 60 to 80 of stars
• helium is the second most common
• together, hydrogen and helium make up 96 to 99
  of all stars

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question
What color is a cold electric stove? How can you
tell when it gets very hot? Which is hotter a
yellow or blue flame?
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Star Temperature
- just as different colors indicate different
temperatures for hot objects on Earth, a stars
color tells us about the temperature at the
surface of the star.
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Star Temperature
- the surface temperature of a star, however,
does not tell us how hot the star is on the
inside.
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Star Temperature
Example our Sun is a yellow star with a surface
temperature of 6,000oC but the temperature at
its core is 15,000,000oC!
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Star light, star bright...
How do stars shine anyway?
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question
What were the two most common element in stars?
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Star Light
- the gravity inside the core of a star is so
strong that it forces hydrogen atoms to smash
into each other and join up to make helium atoms
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this process is called
Nuclear Fusion
- when the hydrogen atoms collide, they release
huge amounts of energy
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Nuclear Fusion
- this energy is released as heat and light,
which is why stars are hot and shine
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Nuclear Fusion
How much energy does fusion release?
- the fusion of 1 liter of hydrogen atoms gives
off more energy than burning one ton of coal
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Nuclear Fusion
How often does fusion occur?
- in our Sun, enough hydrogen atoms fuse every
second to fill a cube with each length the size
of a football field
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Nuclear Fusion
Does fusion occur on Earth?
- only if people make it happen the only use we
have right now is the hydrogen bomb, but someday
it may be an unlimited, clean source of power