Credit: abyss'uoregon'edu

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Credit abyss.uoregon.edu
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More on Gravitation

• Forcegravity G M1 M2 / d2
• Where G, the gravitational constant, is equal to
  6.67 x 10-11 m3 kg-1 s-2
• F m a G MEarth m / d2
• m cancels
• same acceleration felt by everything near the
  Earths Surface

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Solar spectrum displayed like a book
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Tides
Black arrows ?Force due to Moon
High Tide
Low Tide
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The Prism
White light is just a combination of colors of
light just the opposite of paint/markers.
A prism will spread white light into components,
putting a second prism in the path will split the
components further.
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Light as a Wave
Click Here
Frequency how many waves pass by a point
(units of per second) Wavelength distance
between peaks of waves (units of length)

• Speed frequency x wavelength speed of light
• Other properties of waves diffraction,
  interference

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Light as a Particle

• Discrete bits of energy (individual particles)
  termed photons.
• Collisions transfer energy
• (Higher frequency ? higher energy)
• (Shorter Wavelenth ? higher energy)
• Photons are MASSLESS particles
• can travel as the speed of light
• (massive particles cant achieve the speed of
  light in a finite time)

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What is Matter?
Matter is composed of particles, in everyday
experience, mainly atoms (NOT the fire wind,
earth, and water kind of atoms)
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Atomic Structure

• Gravity pulls atoms towards Earth
• Electromagnetic forces bind electrons to atomic
  nuclei but protons in the nuclei repel each
  other
• And the strong force bonds nuclei together (why
  extra neutrons are needed for stability of atomic
  nuclei)

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Atomic Structure(2)
Chemical properties of elements can be grouped
into classes with similar properties based on
atomic number (number of protons). However, the
light emitted/absorbed by atoms is dependent on
the electron configuration, which depends on
temperature (electrons can be lost, e.g.
ionized states).
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Energy Levels
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Distributions of Light
Continuous versus discreet we dont see the
difference (usually) Fluorescence, Incandescent
lights, LEDs, Lasers
http//outreach.atnf.csiro.au
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Interaction of Light and Matter

• Emission
• Absorption
• Transmission/Refraction
• Reflection/Scattering

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Materials with Special Properties

• Translucent vs Opaque
• Mirrors
• Holograms
• The atmosphere, Snow
• Sunglasses
• Photochromic, electrochromic materials
• Dichroic, optical (double image) calcite

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Thermal (Blackbody) Spectra
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Most everything emits blackbody radiation
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Properties of Blackbody Spectra

• Continuous distribution of light (no emission or
  absorption spikes)
• Hotter objects show greater intensity in ALL
  wavelengths, indicating they emit more total
  radiation per unit area.
• Hotter objects emit photons with a higher
  average energy.

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Spectra
Light can be dispersed using a prism, grism, or
grating.
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Absorption Line Spectra
http//outreach.atnf.csiro.au
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Emission Line Spectra
http//outreach.atnf.csiro.au
Click Here
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Both
Different way of displaying spectra more useful
but less colorful.
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How Are Photons Emitted and Absorbed?
Electrons absorb and emit photons when they
change energy.
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Another Example of Emission, Absorption and
Scattering
Click Here
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Spectra of Stars and Galaxies
Stars typically have blackbody spectra with
absorption lines due to outer layer of the
star. Some very hot stars also show emission
lines. Galaxies are collections of billions of
stars, so typically the spectrum is a
superposition of lots of star spectra of varying
temperatures. However, lots of other features
can appear in galaxy spectra more on this later.
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Non-Thermal Spectra
Interactions of electrons, photons and other
particles lead to non-thermal spectra meaning
spectra that arent blackbody or combinations of
blackbody spectra.
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How Are Spectra Useful?
Spectra tell us about the elements and molecules
present, their velocity, pressure, temperature,
ionization state, etc Measurements of spectra
are discreet
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Systems of Lines
Emission and absorption line lines come in
systems, that is, groups of lines related to a
particular element or molecule. We can use these
to uniquely fingerprint a spectrum.
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Doppler Shifts and Redshift

• Dependent on SOURCE velocity wrt the observer.

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What Can We Learn From Redshift
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By measuring systems of emission and/or
absorption lines, we are able to ID and determine
the redshift for most objects.