Newton

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Newtons Experiments with Light
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Electomagnetic Waves
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Properties of Waves Frequency and Wavelength
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Telescopes
Yerkes Refractor
Arecibo Radio Disk
Mauna Kea
Hubble Space Telescope
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Resolution of Telescopes
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Sensitivity of Telescopes
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The Earths Shroud

• The Earths atmosphere acts to screen out
  certain kinds, or bands, of light.
• Visible light and radio waves penetrate the
  atmosphere easiest the IR somewhat. Most other
  bands are effectively blocked out.
• Consequently, telescopes are built at high
  altitude or placed in space to access these
  otherwise inaccessible bands.

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Transparency of the Atmosphere
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Transmission with Altitude
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Flux of Light

• Light carries energy (e.g., perceived warmth from
  sunlight)
• How does this energy propagate through space?
  And how does that relate to the apparent
  brightness of a source?
• Flux describes how light spreads out in space
• with Lluminosity (or power),
• and d distance,
• flux is Watts/square meter J/s/m2

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The Inverse Square Law
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Kirchoffs Laws

1. A hot solid, liquid, or dense gas produces a
   continuous spectrum of emission.
2. A thin gas seen against a cooler background
   produces a bright line or emission line spectrum.
3. A thin gas seen against a hotter source of
   continuous radiation produces a dark line or
   absorption line spectrum.

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Kirchoffs Laws Illustrations
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Blackbodies

1. A common approximation for the continuous
   spectrum produced by many astrophysical objects
   is that a blackbody (or Planckian).
2. A blackbody (BB) is a perfect absorber of all
   incident light.
3. BBs also emit light!

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Temperature Scales
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Temperatures of Note
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Sample Blackbody Spectra
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Atomic Physics

• Atoms composed of protons, neutrons, and
  electrons
• p and n in the nucleus
• e resides in a cloud around the nucleus
• mp/mn1
• mp/me2000

Protons p 1 mp
Neutrons n 0 mn
Electrons e -1 me
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The Bohr Atom
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Atomic Energy Level Diagram
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Interaction of Matter and Light

• Absorption Occurs when a photon of the correct
  energy moves an electron from a lower orbit to an
  upper orbit.
• Emission Occurs when an electron drops from an
  upper orbit to a lower one, thereby ejecting a
  photon of corresponding energy
• Ionization Occurs when a photon knocks an
  electron free from the atom
• Recombination Capture of a free electron

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Absorption and Emission
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The Gross Solar Spectrum
Blackbody-like
Blackbody deviations
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Thermal Motions of Particles in Gases
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Doppler Shift

• The Doppler effect is a change in l, n, E of
  light when either or both the source and detector
  are moving toward or away from one another. So,
  this is a relative effect.

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Illustration of the Doppler Effect
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Composition of the Universe
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Brief Overview of Stellar Evolution

• Pre-Main Sequence (really short time)
• The phase in which a protostar forms out of a
  cloud of gas that is slowly contracting under
  gravity
• Main Sequence (long time)
• The phase in which a star-wannabe becomes hot
  enough to initiate and maintain nuclear fusion of
  hydrogen in its core to become a true star.
• Post-Main Sequence (sorta short time)
• H-burning ceases, and other kinds of burning may
  occur, but the star is destined to become a White
  Dwarf, Neutron Star, or Black Hole

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Formation of Stars and Planets

• Observational Clues from the Solar System
• Orbits of planets lie nearly in ecliptic plane
• The Suns equator lies nearly in the ecliptic
• Inner planets are rocky and outer ones gaseous
• All planets orbit prograde
• Sun rotates prograde

1. Planet orbits are nearly circular
2. Big moons orbit planets in a prograde sense, with
   orbits in equatorial plane of the planet
3. Rings of Jovians in equatorial planes
4. S.S. mass in Sun, but angular momentum in planet
   orbits

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Accretion and Sub-Accretion
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Collection of Planetesimals into Planets
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Solar Nebula Theory

• Immanuel Kant (German) 1775, suggested that a
  rotating cloud that contracts under gravity could
  explain planetary orbit characteristics
• Basic Modern View
• Oldest lunar rocks 4.6 Gyr
• Planets formed over brief period of 10-100 Myr
• Gas collects into disk, and cools leading to
  formation of condensates
• Growth of planetesimals by collisions
• Build up minor bodies and small rocky worlds
• Build up Jovian cores that sweep up outer gases

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The Chaotic Early Solar System

• Recent computer models are challenging earlier
  views that planets formed in an orderly way at
  their current locations
• These models suggest that the jovian planets
  changed their orbits substantially, and that
  Uranus and Neptune could have changed places
• These chaotic motions could also explain a
  spike in the number of impacts in the inner
  solar system 3.8 billion years ago

The Moon and terrestrial planets were bombarded
by planetesimals early in solar system history.
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Cosmic Billiards

• The model predicts
• After formation, giant planet orbits were
  affected by gravitational nudges from
  surrounding planetesimals
• Jupiter and Saturn crossed a 12 orbital
  resonance (the ratio of orbital periods), which
  made their orbits more elliptical. This suddenly
  enlarged and tilted the orbits of Uranus and
  Neptune
• Uranus / Neptune cleared away the planetesimals,
  sending some to the inner solar system causing a
  spike in impact rates

100 Myr
880 Myr
20 AU
planetesimals
883 Myr
1200 Myr
N
U
S
J
The early layout of the solar system may have
changed dramatically due to gravitational
interactions between the giant planets. Note how
the orbits of Uranus and Neptune moved outwards,
switched places, and scattered the planetesimal
population.
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The Big Picture

• The current layout of our solar system may bear
  little resemblance to its original form
• This view is more in line with the planetary
  migration thought to occur even more
  dramatically in many extrasolar planet systems
• It may be difficult to prove or disprove these
  models of our early solar system. The many
  unexplained properties of the nature and orbits
  of planets, comets and asteroids may provide
  clues.

Artists depiction of Neptune orbiting close to
Jupiter (courtesy Michael Carroll)
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Bodes Law
Planet Bodes Actual Error
Mercury 0.4 0.4 lt1
Venus 0.7 0.7 lt1
Earth 1.0 1.0 Perfect
Mars 1.6 1.5 7
Asteroids 2.8 2.8 lt1
Jupiter 5.2 5.2 lt1
Saturn 10.0 9.5 5
Uranus 19.6 19.2 2
Neptune --- 30.0 Miserable
Pluto 38.8 39.4 2
?? 77.2 --- ---
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Radiative Equilibrium
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Global Temperatures of Planets
Planet Predicted Actual Error
(K) (K) ()
Mercury 440 400 10
Venus 230 730 68
Earth 250 280 11
Mars 220 210 5
Jupiter 105 125 16
Saturn 80 95 16
Uranus 60 60 lt1
Neptune 45 60 25
Pluto 40 40 lt1
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Density and Composition
ltrgt (kg/m3)
Water 1000
Rock 3000
Air 1.3
Brass 8600
Steel 7830
Gold 19300
ltrgt (kg/m3)
Ices 1000
Volcanic rock and stony meteorites 2800 - 3900
Iron rich minerals 5000 - 6000
iron 7900
Ex Moon r(surf) 2800 and ltrgt
3300 Earth r(surf) 2800 but ltrgt 5500