Stars and Galaxies Galaxies

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Stars and Galaxies Galaxies

• sStars
• The Sun
• Evolution of Stars
• Galaxies and expanding Universe

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Stars

• Constellations are grouping together of stars by
  first Greeks/ Romans
• They imagined constellations represented
  mythological characters, animals or objects
• Stars in constellations are not necessarily
  clustered close together
• 88 constellations known today

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Circumpolar Constellations

• Earth rotates on its axis
• When looking at the sky, the sky revolves around
  a center point called the North Star (located
  near the handle of the Little Dipper)
• Constellations move around the North Star
  appearing during parts of the year and
  disappearing below the horizon during other times
  of year.
• Some constellations appear year round that are
  near the North Star

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• Some stars can appear very bright but are
  actually are dim stars very close to earth.
• Some stars appear dim but are very bright stars
  but are a great distance from earth
• Absolute Magnitude Actual amount of light given
  off by a star
• Apparent Magnitude is a measure of the light
  received on earth
• Sirius is the brightest star , but is a dim star
  that is 100 times closer than Rigel (a star that
  is farther away). If both the same distance from
  earth Rigel would be so much brighter

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Measurement in Space

• To find distance to stars, astronomers use
  Parallax measurements
• Using angles from earth on its revolution around
  the sun, they can calculate distances to stars

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Measurement in Space

• Units of distance of vast space is recorded in
  light years. It is the distance light travels in
  one year (about 6 trillions miles in one year)

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Properties of Stars

• Color of Star indicates its temperature
• Red stars are relatively cool stars
• Blue/white stars are relative hot stars
• Yellow stars have medium temperatures
• When light passes through a prism, the light is
  divided into its spectroscope ranging from red,
  orange, yellow, green blue, indigo and violet.

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Spectroscope

• When light passes through a prism, the light is
  divided into its spectroscope ranging from red,
  orange, yellow, green blue, indigo and violet.
  (red is cooler, blue/violet is hottest)
• Star light is divided into its colors.
• As the light passes through the stars atmosphere,
  there are black lines in spectrograph caused by
  stars atmosphere absorbing some of its radiation
  depending on the kinds of atoms in its atmosphere

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Spectroscope

• Scientists knows the kind of black lines
  associated with elements in the atmosphere and
  can determine what the composition of the stars
  atmosphere is by looking at those dark lines

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Spectrograph of a star
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The Sun

• Sun is our closet star made up of layers of an
  atmosphere
• Energy is transfer to us through radiation and
  convection

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Suns Atmosphere

• Photosphere lowest layer. Temp is about 6000K,
  known as its surface, but is not smooth
• Chromosphere extends 1200 miles above
  photosphere. Extends through a transition zone up
  to 6000 miles above surface
• Corona is largest layer extends millions of miles
  outward. Temperatures here is as high as 2
  million degrees Kelvin
• Charged particles are emitted though corona and
  move through space as solar wind

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Suns Layers
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Surface Features

• Sun spots dark areas that are cooler
• Sunspots rotate as does the sun and can follow
  the spots
• Rotates faster at equator, slower at poles
• Sunspots cycle every 10-11 years
• Prominences and Flares
• Intense magnetic fields associated with sunspots
  might cause prominences (huge arching columns of
  gas)

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Surface Features

• Solar Flares violent eruptions of gas near
  sunspots shoot outward at great speeds
• CMEs are coronal mass ejections of electrical
  charged gasses
• Can damage earths satellites, interfere with
  radio and power distribution equipment. Produces
  auroras in northern hemisphere

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Average Star The Sun

• Middle aged, absolute magnitude is about average
• Shines yellow light
• Takes 8 minutes for light to reach earth
• It is unusual in fact it is found as a single
  star (normally stars are in groups of 2 (binary
  system)
• Star clusters group of stars that have a
  gravitation attraction to each other
• Appear fuzzy in sky. Pleiades star cluster is
  obvious in winter skies .. Far from solar system

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Evolution of Stars

• Stars in the sky might appear similar, but are
  quite different
• Hertzsprung and Russell observed characteristics
  where higher temperature stars also have brighter
  absolute magnitudes
• Developed a graph that showed this relationship
  called the H-R diagram (Temperature along
  horizontal axis and brightness in the vertical
  axis)

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H-R Diagram
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Main Sequence Stars

• Diagonal band that runs from upper left to lower
  right within the H-R Diagram
• This gives a continuous flow of how a star is
  born and how it becomes older. A main sequence
  star moves through the band as it ages
• Upper left is hot bright stars, lower left is
  cool din stars
• Our sun is in the middle indicating middle age
  star
• 90 of all stars are a main sequence star
• 10 of stars arent part of Main Sequence
• Some are hot but dim (lower left called white
  dwarfs)
• Some are bright and cool (upper right called
  giants)

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Dwarfs and Giants
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Generating Energy

• Hydrogen fuses together to form Helium with great
  release of energy.
• It releases electromagnetic energy in the form of
  light, infrared, and ultraviolet light. Tiny
  fraction of light reaches earth
• During fusion, 4 Hydrogen atoms fuse to form
  Helium where small amount of mass is lost to
  energy in reaction (large amount of energy is
  released)
• Fusion occurs in cores of all stars. In the core
  of stars the temperatures are high enough to fuse
  atoms

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Evolution of Stars

• As more and more H atoms are fused together, the
  fuel is depleted
• Stars evolve depending on its original size
• Birth of Stars begin as a large cloud of gas
  and dust called nebula. Gravity will pull gas
  and dust together which eventually causes an
  unstable condition. It breaks into smaller
  pieces that eventually become a new star
• Star is born when pieces move closer together,
  temperature increases. When Core reaches 10
  million degrees K, fusion begins. Energy is
  released and star is born

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Evolution of Star

• When stars begin the fusion process, they follow
  the Main Sequence stars path
• When H is depleted, the balance between the
  gravity and pressure no longer exists.
• Core contracts, temperatures increase, outer core
  expands and cools and forms a late stage life
  cycle called a giant
• When temperatures reach 100 million degrees K,
  helium begins to fuse to form Carbon in giants
  core
• The giant has expanded to an enormous size and
  its out layers are much cooler. Our Sun will be
  a giant in about 5 billion years

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White Dwarfs

• When He is eventually used up, core contracts
  inward and out layers escape into space
• Leaves behind hot, dense core
• Our sun will become a white dwarf and the sun at
  this stage is about size of Earth
• It will finally cool and stop giving off light

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Supergiants and Supernovas

• If a star is 8 times more massive than out sun,
  the stages are different
• Cores heat up to much higher temps, heavier
  elements fuse together and star expands to
  supergiant.
• Eventually Fe forms in the core, and Fe cant
  fuse to produce energy
• Core collapses violently and shock waves travel
  outwards
• Outer portion of star explodes producing
  supernova
• Neutron stars if collapsed core of supernova is
  between 1.4 to 3 times as massive as the sun, it
  will shrink to about 12 miles in diameter and a
  neutron star forms
• These are so dense that a teaspoon would weigh
  more than 600 million metric tons

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Black Holes

• If remaining core of supernova is more than 3
  times more massive as the sun, probably nothing
  can stop the cores collapse. The core collapses
  to a point
• Gravity is so strong that nothing can escape from
  it, not even light
• When light cant escape, it is called black hole
• Black holes has an event horizon that if light
  enters it will enter the black hole
• If an object does not cross the event horizon it
  will not be drawn into the hole, rather orbit
  around black hole

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Recycling Matter

• Star begins its life as a nebula, (parts of old
  stars that ejected enormous amounts of matter
  during its lifetime)
• Star cores created during supernovas produce
  larger atoms of carbon and iron
• These stars formed from supernovas and nebulas
  contain heavier elements that could only have
  formed from recycled stars
• Our sun isnt large enough to produce Fe in
  atmosphere, so the Fe had to have come from stars
  that died many Billions of years ago
• Some elements condense to form planets. Our
  bodies contain many atoms that were fused in the
  cores of ancient stars
• Are we are just recycled stars??????

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Interactive H-R Diagram

• http//aspire.cosmic-ray.org/labs/star_life/hr_int
  eractive.html

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Galaxies and the Universe

• Galaxies large group of stars, gas and dust
  held together by gravity
• Earth and our solar system belong to the Milky
  Way Galaxy which is made of a trillion stars
• It is found close to 45 other galaxies known as
  the Local Group
• These galaxies are separated by millions of light
  years.

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Types of Galaxies

• Sprial Galaxies spiral arms that wind outward
  from center
• Milky Way is a spiral galaxy
• Can be normal or barred

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Galaxy types

• Elliptical Galaxies shaped like large 3
  dimensional ellipse. Looks like a football.,
  some are round
• Some of these galaxies are huge fitting several
  Milky Ways into one

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Irregular Galaxies

• Galaxies that dont fit into other two. Many
  different shapes

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Milky Way Galaxy

• 100,000 light years across
• Sun is located 2/3 way from the center
• Takes 225 million years for sun to rotate around
  the center
• Classified as normal spiral galaxy (recent
  studies show think it might be barred)
• Milky Way is spread across the sky in a misty
  band
• Black hole found in center (2.5 million times
  more massive as the sun)

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Origin of Universe

• Steady state universe has always existed, new
  matter forms in center and expands outward
• Oscillating model universe began to expand,
  then contracted and oscillated between expansion
  and contractions
• Big Bang Theory universe began with a big bang
  and has expanded ever since

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Expansion of the Universe

• Doppler Effect a shift of wavelengths (sound or
  light waves) that reflect a change of pitch or
  change of spectrograph
• As a train approaches you the wavelengths are
  compressed and pitch is high, as it passes the
  wavelengths are expanded and pitch is lower
• Light does same thing, rather a shift on the
  spectrograph toward to red it is going away from
  earth, and if shifted to blue it is approaching
  earth

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Doppler Shift
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Big Bang Theory

• Occurred about 13.7 billion years ago
• Entire universe began expanding at the same time
• Hubble Telescope shows more than 1500 galaxies at
  distances of more than 10 billion light years
  away.
• These galaxies could date back to when universe
  was no more than a 1 billion old and are in
  different states of developments
• Will the universe expand and gravity will begin
  to contract back to a single point
• Whether the universe will continue to expands
  depend on the dark energy that is causing the
  universe to expand faster