The Earths Shroud

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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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Flux of Light

• Light carries energy (e.g., 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/sq meter J/s/m2

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• So, a 100 Watt light bulb outputs 100 Joules of
  light energy every second. And it emits equally
  in all directions (roughly).
• This means that when you see such a bulb, only a
  fraction of the 100 Watts impinges upon your eye!
• And the closer you get, the more light you
  receive.

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Telescopes
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Telescope Issues

• Types
• Refracting (lenses)
• Reflecting (mirrors)
• Observing Factors
• Sensitivity or light collecting power
• Resolution (spatial and spectral)

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Kirchoffs Laws

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

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Blackbodies

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

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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

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Interaction of Matter and Light

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

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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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Composition of the Universe
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Brief Overview of Stellar Evolution

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

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

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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