General Astrophysical Concepts: Astronomical length scales and time scales

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Solar system 9 light hours diameter
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Spiral galaxy 80,000 light years diameter
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Coma cluster of galaxies 2.5 million light years
across
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Survey of distant galaxies 5 to 9 billion
light-years away
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Cosmic Microwave Background Radiation (after-glow
from the Big Bang) - edge of the observable
Universe 14 billion light years away
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General Astrophysical Concepts Astronomical
length scales and time scales

• First principles of cosmology
• The universe is (a) HOMOGENOUS (b) ISOTROPIC
• Homogeneity implies isotropy,
• But isotropy does NOT imply homogeneity

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Kepler's laws of motion

• (1) Orbits of planets follow ELLIPSES with the
  Sun at one of the two foci
• (2) Equal areas are swept out in equal intervals
  of time
• (3) P2 a R3 or P2 C R3 / M
• where P is the period of the orbit, R is the
  radius' of
• the orbit, and M is the mass of the central
  object (Sun)

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Elliptical path/orbit followed by planet
Sun
?
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Sample Pop-quiz

• Which of the following statements is TRUE
• When galaxies collide, it is very common for
  stars to smash into each other
• Primordial density fluctuations grow under the
  influence of the electromagnetic force
• Large galaxies are assembled by the merging of
  smaller galaxies
• The furthest galaxies we can see from Earth are
  100 billion light years away

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Forces of Nature

• Newton's Laws of Motion
• Inverse square law of forces
• Fundamental forces (4)

(3) Weak nuclear force Example
ß-decay or top bottom quark (4)
Strong nuclear force Example force
that binds protons neutrons in
atomic nuclei
(1) Gravitational force Example
falling apple (2) Electromagnetic force
Example horseshoe magnet
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The Milky Way and Other Galaxies Like It

• Overview of its constituents
• Dynamics (and mass) of a typical spiral galaxy
• The Milky Way
• Application of Kepler's third law (math
  application)
• - The Solar System and Milky Way
  compared
• - How many stars does the Milky Way
  contain?

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The Detailed Structure of a Spiral Galaxy
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Electromagnetic Radiation

• Propagation of Energy in the Form of Oscillating
  Electric
• and Magnetic Fields
• Speed of propagation (in vacuum) c 300,000
  km/s
• Frequency ? number of oscillations per second
• Unit of frequency s-1 or Hertz (Hz)
• Wavelength ? distance traveled during one
  oscillation
• Unit of wavelength meter (m), Angstrom (1
  Å 10-10 m)
• c ?? or ? c/? or ? c/?
• ? ? are inversely proportional to each
  other

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Electromagnetic Spectrum

• Progression of frequency or wavelength
• Radio, millimeter, sub-millimeter,
  microwave, infrared, optical, ultraviolet, X-ray,
  gamma rays
• Optical/visible white light spectrum (rainbow
  colors)
• Red Orange Yellow Green Blue Indigo Violet
• Order of decreasing wavelength, increasing
  frequency

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Atmospheric Windows

• Optical, sub-millimeter, millimeter, and radio
  wavelengths
• Impact on astronomy (and on human evolution!)

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Sample Pop-quiz

• Which of the following statements is FALSE
• When galaxies collide, it is very common for
  stars to smash into each other
• Primordial density fluctuations grow under the
  influence of the gravitational force
• Large galaxies are assembled by the merging of
  smaller galaxies
• The furthest galaxies we can see from Earth are
  about 10 billion light years away

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Black Body Radiation

• Perfect emitter of radiation perfect absorber of
  radiation
• Energy radiated per second depends on
  temperature
• L AsT4 or L 4pR2sT4 (sphere of
  radius R)
• where L luminosity (in erg/s) A
  surface area
• s Stefan's constant T temperature (in
  Kelvin C 273)
• Quality' of radiation (? or ? or color) depends
  on the
• black body temperature (Wien's law)
  ?peakT constant (?peak is inversely
  proportional to T)

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Black Body Radiation
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Wave-Particle Duality

• Radiation consists of energy bundles (quanta)
  called photons
• Energy of each photon E h?
• where h Planck's constant, ?
  frequency of radiation
• Energy of each photon depends on color'
  (?, ?) of radiation
• The more luminous a source of radiation, the more
  photons it emits per second

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Atomic Energy Levels

• An atom in Quantum Mechanics discrete energy
  levels
• Transitions between levels emission
  absorption lines

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Continuum, Emission Line, and Absorption Line
Radiation