Stars Galaxies Universe - Ch 2

							Stars, Galaxies & the
      Universe
       Chapter 2
            Stars – Section 1
   Stars are identified by several
    characteristics
     Color
     Composition
     Temperature
     Brightness
               Color of Stars
   Star temperature can be found by the
    color, just like flame colors
     Red & yellow are cooler
     Blue is hotter
     Betelgeuse is red & cooler
     Rigel is blue & hotter
                 Composition
   Stars are primarily made up of 2 elements
     Hydrogen
     Helium

   Some stars also have
     Calcium
     Other metallic elements
            Light Spectrum
 White light is made up of the colors of the
  rainbow: red, orange, yellow, green, blue,
  indigo, violet
 A continuous spectrum means all colors of
  light are present
 Hot, solid objects emit a continuous color
  spectrum
 A spectrograph is an instrument to break
  light into a spectrum
      Light Spectrum Cont’d
 Gases give off different color spectrums
  based on the type of gas
 These are called emission lines, which are
  different than a continuous spectrum
                Star Spectrum
   A star’s atmosphere
    absorbs light produced
    from it’s core
   This produces an
    absorption spectrum
   This produces black
    lines in the continuous
    spectrum
   The pattern of black
    lines shows which
    elements are in the
    star
               Temperature
 Stars are now classified by how hot they are
 The color of the star determines the
  temperature
 Star surface temperatures
                  o
     Blue: >30,000 C (10 Lacertae)
                                o
     Blue-white: 7,500 – 30,000 C (Rigel)
                                  o
     Yellow-white: 6,000 – 7,500 C (Canopus)
                           o
     Yellow: 5,000 – 6,000 C     (our sun)
                             o
     Orange: 3,500 – 5,000 C (Aldebaran)
                   o
     Red: <3,500 C (Betelguese)
                 Brightness
 Early astronomers classified stars by
  brightness using their eyes
 First magnitude stars were the brightest
 Sixth magnitude stars were the dimmest
 Telescopes made it easier to see even the
  dimmest stars
 Positive and negative numbers were used
     Positive numbers are dimmer stars
     Negative numbers are brighter stars
                      Magnitude
   Apparent magnitude is how bright a star appears
       Distance, star size, and energy output all determine
        how bright a star appears
   Absolute magnitude is the actual brightness
       Calculated by using the apparent magnitude and
        distance to Earth
   If stars were all the same distance away, then
    apparent magnitude = absolute magnitude
   Our sun is the brightest star in our sky
       Absolute magnitude = +4.8
       Apparent magnitude = -26.8
    Star Life Cycle – Section 2
 Birth
 Adult
 Old
 Very Old
 H-R diagram
                   Star birth
   A nebula consists of hydrogen &
    helium gas and dust
   Gravity pulls the cloud together
    into a dense sphere
   As cloud gets denser, it gets
    hotter
   1st Stage - nuclear fusion of
    hydrogen into helium marks star
    birth (10 million years)
   Size depends on size of nebula
                 Adult Star
 2nd and longest stage (up to 10+ billion years)
 Called the main sequence
 Tremendous energy created in core by
  nuclear fusion
 Size of star doesn’t change as long as there is
  a supply of hydrogen
                  Old Star
 3rd Stage (millions of years)
 Called a red giant or red supergiant
 Hydrogen supply used up
 Core shrinks
 Atmosphere expands and cools
 10 to 100 times bigger than our sun
                  Very Old Star
   4th and final stage
   Called white dwarf – stars same size or smaller than sun
   Left over center of a star
   No hydrogen left
   Can’t generate energy by fusion
   Shine for billions of years as they cool
                    H-R Diagram
   Ejnar Hertzsprung – Danish (1911)
   Henry Russell – American (1913)
   Graph that shows relationship between
       Star surface temperature
       Absolute magnitude
   Shows life of stars
       Main sequence (blue, blue-white, yellow, red)
       Red giant or supergiant
       White dwarf
   Classifies stars
        H-R Diagram


                      Red giants

Blue stars


               Main
               sequence



White dwarfs
                            Red dwarfs
              Very Old Blue Stars
   Very massive stars may
    explode
   Are very hot & use energy
    quickly
       Short lived
   Supernova
       All hydrogen used up
       Star explodes in a flash brighter
        than a galaxy
       Star then collapses on itself
Supernova
               Supernova Effects
   Center of star compressed into a new star
   Neutron star
       Particles formed into neutrons
   Pulsar
       Spinning neutron star
       Radiation beam spins rapidly
       Detected as clicks or pulses by radio telescopes
   Black hole
       Leftover supernova so with gravity so powerful that not
        even light can escape
       Can be detected by stream of gas or dust spiraling into
        black hole and emitting x-rays
Neutron stars, Pulsars, Black Holes
           Galaxies – Section 3
 A group of stars, gas & dust is a galaxy
 Galaxies can contain up to a trillion stars
 Types of galaxies – classified by Hubble
     Spiral
     Elliptical
     Irregular
                   Galaxy Contents
   Nebulas
       Large clouds of gas & dust
       Regions where stars form
   Star clusters
       Globular
       Open
   Globular cluster
       Often in spherical halo of a spiral galaxy
       Group of up to a million older stars
   Open cluster
       In spiral disk of a galaxy
       100s to 1,000s of newer, blue stars
         The Universe – Section 4
   Cosmology – study of the origin of universe
   Universe in expanding
       Hubble used Doppler red shift of galaxies
       Raisin bread model
   Big Bang Theory
       13.7 billion years ago
       All matter in universe compressed together into a very
        small spot
       Universe rapidly expanded, matter came together, and
        galaxies starting forming
       Cosmic background radiation leftover from Big Bang