Science 9: Unit E: Space Exploration

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Science 9 Unit E Space Exploration

• Topic 3 Spectroscopy and the Doppler Shift

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White Light is Made of a Spectrum of Colours.

• White light is made up of a spectrum of colors.
  The spectrum of colors starts with red, orange,
  yellow, green, blue, indigo, and violet/purple. A
  spectroscope is a device used to show the
  spectrum of colors given off by a light source.
  It works by having the light pass through a
  series of prisms which break up the light into
  colors.

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Dark Line Spectrum

• When a spectroscope was place in the path of
  sunlight it was discovered that sunlight did not
  give off a continuous spectrum. There were dark
  gaps in the suns light spectrum. These lines or
  were called spectral lines.

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Element Spectra

• Two German scientists Kirchoff and Bunsen
  discovered that by heating elements until they
  glowed (incandescence) they gave off a spectrum
  of their own. A particular element gives its own
  signature spectrum with its own spectra lines.

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Spectral Analysis

• Every star gives off its own signature spectrum.
  What makes the spectrum unique is the position of
  the spectral lines in the spectrum.
• Just like stars, elements, when heated, give off
  their own signature spectrums, with their own
  particular pattern of spectral-lines.
• The location of the spectral lines tells us what
  elements are in the star. By matching the pattern
  of spectral lines coming from a star to the known
  spectral patterns of elements you can determine
  the composition of a star.

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Doppler Effect, Big Bang, and Red/Blue Shift

• Astronomers noticed that distant stars and
  galaxies gave off spectral patterns of their own
  which matched known elements. However, the
  patterns were all shifted to the red end of the
  spectrum. At first no one knew what this meant.

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Sound and the Doppler Effect

• When a source of sound, like a police siren,
  moves towards an observer, the waves bunch up and
  the sound goes higher in pitch.
• When the police car moves past and away from you,
  the sound waves spread out and the sound goes
  lower in pitch.

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Light and the Doppler Effect

• The same thing happens with light. When a light
  source moves away from you, the light waves shift
  to the red end of the spectrum (lower frequency),
  when the light source moves towards the observer
  the light waves shift to the blue end of the
  spectrum (higher frequency).
• So What does this mean?
• The fact that the spectral lines are all shifted
  to the red end of the spectrum meant that the
  stars/galaxies and us are moving away from each
  other.

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The Doppler Effect and the Big Bang Theory

• Scientists then theorized that if were all
  moving away from each other that we must have
  started out together which gave us the Big Bang
  Theory. Everything in the universe started in a
  tiny point of space and then exploded apart, the
  Big Bang. Were still exploding now, eventually
  the universe like an elastic-band will stop going
  out and eventually start pulling back in to that
  same point in a Big Crunch.

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Types of Spectra

• I. Emission/Bright Line Spectra A series of
  bright colored lines produced against a black
  background. These spectra are produced when a gas
  is heated at low/normal pressure. The easiest to
  produce and see.

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Types of Spectra Continued.

• II. Continuous Spectrum The full spectrum that
  you see in the rainbow. These are produced when a
  gas is heated at high pressure or a solid or
  liquid is heated.

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Types of Spectra Continued

• III. Absorption/Dark Line Spectra The kind of
  spectra weve been studying. The continuous
  spectrum with a series of dark gaps (spectral
  lines). These are produced when a gas is heated
  at high pressure and then has to pass through a
  much cooler environment.

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Diffraction Gratings

• A piece of transparent materials (such as plastic
  or glass) with thousands of closely spaced slits
  in it. This allows light waves to bend around the
  edges and interfere with each other producing
  areas of constructive interference (bright lines)
  and destructive interference (black gaps).
• Modern spectroscopes use diffraction gratings
  instead of prisms because they produce much
  better detail in showing spectral lines from star
  spectra.