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									Physics and Astronomy
  A Little Physics will help you
    Understand Astronomy
   Introduce most Important Concepts
    • Not 2 years of Physics in one night!
   Encourage you to explore on your

   Some Simplifications Introduced
    • Allows Better Focus on Key Points
   Several Models of Physics
   Planet Orbits
   General Relativity
   Light
    • Spectra
    • “Black Body”
    • Emission and Absorption
    • How Astronomers use Spectra
           Models of Physics
   Classical (Newtonian)
    • Everyday world
   Relativity
    • Fast or Planet Size Heavy
   Quantum Mechanics
    • Atomic
              Classical Physics
   Physics of the Everyday world
   Principle Contributors
    • Newton
         Kepler For Astronomy
   All Objects have Defined Behavior
    • Location, Energy, and Mass
              Classical Gravity
   Force that declines with square of distance
   Very weak
   Newton only predicted effects not cause
Fun with Ellipses

Kepler’s Laws

Planetary motion
   Light carries Energy
   Light behaves like ripples on pond
    • (sometimes)
   Distance between ripples is
   Shorter Waves => Higher Energy
   Different Wavelengths perceived
               Light as Waves
   Any Obstruction causes
   Reduces ability to see fine


   In 1900 Classical Physics =>
    • Fixed Frame of Reference & Time
    • Worked Well for Everyday problems
   Did not Explain
    • Orbit of Mercury
    • Speed of Light
    • What is Gravity?
     Einstein – Special Relativity
   1905 - Einstein Recognized Speed of
    Light Fixed
    • Speed of Light Constant
    • No Absolute Space or Time Reference
    • Everything depends on Observer
   “Special Relativity”
    • Deals with Objects moving fast
    • Not as important for our use
    Einstein – General Relativity
   Special Relativity Did not Explain
   1915/6 Einstein expanded 1905 work
    • General Relativity
   Gravity is Curvature of Space/Time
    • Gravity Bends Light
    • Predicts Orbit of Mercury
    • Black Holes
    • Big Bang
      Representing Space/Time
   “Great Circle” similar problem
   Difficult to visualize Effect of
    Spherical Earth
   Everyday World seems Flat
    • Grid is a good approximation
         Pitchers do not correct for Curved Earth
         “Great Circle” on earth
   Which direction is
    shortest to Paris
    • Chicago or Calgary
If you could picture the 3rd
Gravity as warped space
     The Perihelion of Mercury
   Location of closed approach drifts
    • No Newtonian Mechanism for this
   Curvature SpaceTime changes orbit

         Gravitational Lensing
   Warped Space
    bends light
   First Confirmed
    by Eddington in
    • Star visible
      during Solar
      Eclipse         wiki
   Best Evidence
    for Dark Matter
         Black body radiation
   Hot Material emits Light
    • Hotter =>
    • More Energy =>
    • Shorter wavelength
Hotter Stars are Bluer
    What about Something REALLY Hot

   Penzias & Wilson
    found in 1965
   Black Body @
    2.725° K
   Best Evidence for
    Big Bang
          COBE and WMAP
   Satellite Observation supports current
   Mostly uniform, but with enough lumps
    to form structures
Quantum Mechanics
   Atomic Behavior
              Light (Revisited)
   Electromagnetic Energy
   Carried by photons
    • Behaves as both particle and wave
   Has Define Energy
   Particle Behavior
    • Photoelectric Effect
    • CCDs
   Wave Behavior
    • Diffraction
    • Short WL = Higher Energy
          Tuning Fork Analogy
   Tuning Fork only
    emits single freq.
   A sound of that
    freq will cause fork
    to vibrate
    • Any other freq
   Hitting a fork
    causes vibration +
    The Bohr vs. Quantum Atom
   Bohr Modeled like Solar Systems
    • Still taught in Introductory Courses
    • Known by 1920s that was wrong picture
   Quantum Mechanics
    • Mathematical Model
    • Difficult to map onto everyday world
             The Real Atom
   Electrons form Cloud around nucleus
    • Cloud has several Configurations
   Changing Configs requires Energy
    • Only certain energies (wavelengths)
    • Just Like a row of Tuning Forks
   Atom Emits exact energy to move to
    lower state
   Light Behaving as Particle
   High Energy (shorter WL) Photon=>
    • Atom moves to higher energy config +
    • Heat
   Atom returns to lower Energy State
    • Emits photon with < Original Energy
         Photon has longer wavelength
         Spectra (Absorption)
   White Light through thin gas/plasma
    • Each Element Absorbs Its Levels
    • Voids where light absorbed
    • Amount of Absorption proportional to
    • Chemistry affects Spectra
            Spectra (Emission)
   Florescence
    • Energy Source =>
      Low Pressure Gas
   Examples
    • LP Sodium Streetlight
    • M27

How Astronomers Collect Spectra
            Doppler Shift
   Motion Changes Wavelength

         Doppler and Spectra
   Carefully measuring spectra gives
    Relative motion
    • Red = away
    • Blue = toward
Hubble and Expanding Universe
   Slipher measured Red Shifts of
   Hubble combined data to show
    expanding universe
    • Space itself is expanding
   Recent Lick work shows rate
           Gravity (Revisited)
   Both objects orbit around common center
    of gravity

     Sun        Center of Mass
            Discovering Planets
   Star orbits around center of mass
    • Close to but not exactly center of star
   Star moves relative to Earth
    • Movement causes Doppler Shift
         Can be measured
   Amount => Mass of Planet
   Period => Orbit
    Some Other Topics to Explore
   Cosmology
    • Inflation
    • Where is the Anti-Matter?
    • Dark Energy, Matter
   Modern Thoughts on Space Time
    • Hawking, et al
   What is Gravity
  Simple Math Disproves Astrology

                   Planet Mass         Distance            Gravity
                      10^22 Kg            (moon=1)           (moon=1)

Jupiter                     200,000                  630                          0.01

Moon                             7.4              0.384                                    1

                                                           Table from Bad Astronomy site

 Effect of Floor of Delivery Room even greater!

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