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					400 Years of Cosmic Discovery

  Instruments, patterns, and theory
             Tim McKay
   Saturday Morning Physics 2/7/09
      Written by:
Norriss S. Hetherington
  W. Patrick McCray
An Alternate Universe

Constructed of two
completely separate
parts: Heaven and

The Earth: made of
earth, air, fire, and
water. Earth is the
realm of transience.

The Heavens: perfect,
eternally regular, and
impossibly remote. The
Heavens are realm of
the eternal.

This is the universe into
which Galileo was
       Our Universe

A cosmos of infinite
                                          Machines we construct
                                          wander the solar system
                                          and beyond.
Everything , down to the
atoms we’re made of,
                                          Our augmented eyes
comes from the heavens
                                          probe the cosmos in space
                                          and time, right back to its
Energy floods daily down
                                          hot, dense beginning
from the Sun, enabling life,
then flees back into space

     Instruments               Patterns                   Theory
Instruments   Galileo and the telescope
     • In 1609, Galileo heard
       rumors of a device for
       magnifying your view, a
     • He promptly built his own
       3x version, then quickly
       improved it to 30x
     • This telescope also
       effectively made his eye
       larger, gathering more
       light                       Portrait by Tintoretto, probably from
                                             around 1610-1615
              How does a telescope work?
     • An “objective” lens (or mirror!) forms an
       image of distant objects
     • An “eyepiece” can then be used as a magnifier
       to allow you to view this image
     • You only need this eyepiece if you want to
       view the image with your eye…

                            What does 3x magnification do
                                      for you?

       What does 30x magnification
              do for you?



                                          Sunspots in May 1612
        Phases of Venus
UM Special Collections on the 7th floor
of the Hatcher Graduate Library is
opening and amazing display of early
astronomical texts, instruments, and
documents from February 9 – April 11.

This will include first editions of
Siderius Nuncius, along with the work
of Kepler, Copernicus, Brahe, etc.

            Kepler divines regularities…
• Kepler analyzes planetary
  observations from Tycho
  Brahe: 1609
• Finds precise patterns in
  their motions
• Encodes these in three
  unexplained “laws”
      – Planets orbit in ellipses
        with the sun at one focus
      – Their speeds change,
        sweeping out equal areas
        in equal times
      – Their orbital periods vary
        like (orbit size)3/2
           Newton solves the
Theory       solar system
    • Two tasks
         – Explain all mundane
           motion with               1687
         – Universal gravity
           unites apples falling
           with planets orbiting   Blake
    • The precision of his
      success was shocking
      to his contemporaries

    Nature and nature's laws lay
      hid in night;
      God said "Let Newton
      be" and all was light.
                 Alexander Pope
Instruments   Newton’s instruments: 1670
         Reflecting telescopes
                                                        The spectrograph

                                                 “Disperses” light into its constituent
                                                 colors, here using a prism. Newton also
    Uses a mirror as the objective, eliminates   reassembled these colors…
    chromatic aberration, allows for very
    large objectives supported from behind!
           Fraunhofer and the dark
            forest in the Sun: 1814

Joseph Fraunhofer, seeking to understand dispersion in glass and
eliminate chromatic aberration, constructed the world’s best
spectrographs. He found a forest of hundreds of dark lines
interrupting the spectrum of light from the Sun…
                                                            K       B
                Partial understanding of
             Fraunhofer’s dark forest: 1859
 • Kirchoff and Bunsen:
   interactions between            • Specific elements emit
   light and matter                  and absorb specific sets
           – Hot dense object:       of frequencies
             continuous spectrum
           – Hot diffuse gas:
             emission line
           – Hot dense object
             surrounded by
             tenuous gas:
             absorption line
             spectrum                It’s possible to tell what a
                                     distant object is made of!
                         Your basic spectrograph

                             A prism or diffraction
                          grating “disperses” the light     Light comes
   Light goes in here                                         out here
                                                                            We add a
                                                                            here to see
     A narrow slit for                                     A microscope     for us
       collimation                                        for viewing the
                                                          dispersed light
         Spectral lines and Doppler
         shifting: detecting motion


                                         Moving   Many quasar
                                         away     spectra
                                         faster   sorted in
                                                  order of
                    All lines shift to            velocity
                    longer wavelength
                                                  X. Fan, Ariz.
Theory              Skipping a bit…
    • Great physics               • Involves many fields
      achievements of the             – Thermodynamics
      19th and early 20th             – Electricity and
      century                           magnetism
    • A thorough predictive           – Statistical physics
      theory of the                   – Quantum mechanics
      interaction of light and
      matter                      • This knowledge allows
    • Can predict what light        interpretation of the
      an object will emit or        complex spectra of
      absorb                        distant objects
  Cecelia Payne-Gaposhkin promptly put these principles to work…
         Cecelia Payne-Gaposchkin finds out
         what the universe is made of: 1925
               Stellar classes (OBAFGKM…)
               don’t reflect different
               chemical composition, but
               just different temperatures

               She showed that all stars
               are made primarily of
               hydrogen and helium: light
               elements are dominant!

               This is remarkable. What
               we are made of is
               abundant, but rare…

The sequence of spectral classifications is a sequence in temperature!

  Draper, 1880, from the Harvard Plates

Photography exposes a new
view of the universe…

                                          A. A. Common, 1883

              George Ellery Hale
              Yerkes 40”   Mt. Wilson 60”
                 1895          1908

                                        Mt. Wilson 100”
                                        Hooker Telescope
              Mt. Palomar 200”
               Hale Telescope
Instruments         1948
                               Brighter “Cepheids“
                               pulsate more slowly: 1929

           Henrietta Leavitt

• Edwin Hubble and
  Milton Humason
  used the 100” to
  detect Cepheids in
  nearby galaxies
• Meanwhile, Vesto
  Slipher measured
  galaxy spectra,                 1000 km/s

  finding that
  they’re moving

  away from us!
         Einstein’s dynamic universe: 1917

• In general relativity
  space-time is intrinsically
• Matter influences space-
  time curvature
• Space-time curvature
  tells matter how to move
• GR naturally
  expanding (or
  contracting) space-time!      R  1 Rg   8GT
                             Seeing the rest…

 Sadly, most of the light
 which arrives from
 distant objects is
 absorbed by the

 Only optical light and
 radio waves readily
 penetrate from space
 to the ground.

 To avoid this,
 instruments must be
 placed above the
 atmosphere, on
 mountains, planes,
 balloons, and satellites.
Instruments                Fermi GLAST

Multi-wavelength astronomy, like spectroscopy, provides a new view

    X-ray     Extreme UV    Ultraviolet       X-ray          Optical

   Visible     Calcium K    Hydrogen        Near IR          Mid IR

                 Radio                        Far IR           Radio
                                             M104: the Sombero galaxy
              Digital detectors collect 40-80x
              as much light as photographic
Instruments   plates! 1980 and beyond…

              This is like making your
              telescope suddenly 40-80x
              Computers are completely revolutionary. They allow us to
              gather massive quantities of data, analyze it precisely, share it
              globally, and make precise predictions for complex phenomena

                              Mare Nostrum Supercomputer
                                     in Barcelona
              20th century astrophysics
   • An enormous record of       • Major (and many minor)
     progress, the subject of      mysteries remain
     many talks this term           – Dark matter
   • A solid origin theory for      – Dark energy
     everything we see; the      • These are today’s robust
     hot big bang cosmology        patterns for which we
   • This is an enormous           lack adequate
     achievement, the fruit        explanation, like
     of 400 years of hard          Fraunhofer’s dark lines…
Instruments           The future?                          Theory

     • More of everything, but • Our data will be much
       not incomprehensively     better; more precise,
       more…                     deeper, comprehensive
     • Our map of the universe • Computation will likely
       is filling in             be able to handle the
     • Its major features will   challenge
       be mapped during our    • We will also get some
       lifetimes                 wholly new data
     • Don’t despair, this       (gravity waves for
       leaves plenty to do…      example…)
Patterns       New worlds, new life
    • Before 1995 we thought     • The great triumph of
      planets must be there,       astrophysics is unifying
      but couldn’t prove it        heaven and earth
    • Now we have found          • Life is here, a vibrant,
                                   robust physical process,
      many hundreds, with          it should emerge readily
      thousands to come…
                                 • This will be the next
    • Today we think that life     (and last?) great step in
      must be widespread,          unification, so let’s get
      but we can’t prove it        started!