How%20Far?

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How Far?

• Measuring Distance in the Universe

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How?

• Gian Domenico Cassini, in 1672, used a technique
  called parallax to measure the distance to Mars.

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Cassini figured it out!

• The Sun is about 93 million miles from
• Earth. As Earth and Mars never come closer than
  35 million miles to each other.
• Saturn, the most distant planet known when
  Cassini was alive, is around 900 million miles
  away.

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How?

• Parallax!

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What is Parallax?

• Try this out
• Hold 1 finger out at arms length
• Close one eye, and then the other
• Notice how your finger jumps?

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Measuring Stars

• Stars are billions of light years away winking
  wont help
• Our orbit is 186 million miles wide (93 million
  93 million)
• Star A and B are the same star, as they appear 6
  months apart

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How to

• The parallax angle p is illustrated in the above
  figure.
• We can determine they adjacent (d) using
  trigonometry.

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Trigonometry

• Our adjacent line (d in the prior picture) is the
  distance from Earths Orbit (BC) to the star (A)
• Adjacent length opposite length tangent angle A

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Trigonometry

• Measure the angle of the star to our central
  point of orbit
• Simple calculation
• Even the Hubble Telescope limited to 1000 LY

Earths Orbit
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Parsec

• The method of parallax gives rise to a natural
  distance unit that astronomers call the parsec.
• defined as the distance at which a star would
  have a parallax angle p equal to one second of
  arc.
• using trigonometry distance equal to 206,265
  astronomical units or 3.26 LY
• AU is the average distance of Earth to Sun

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Further away?

• The universe is expanding
• Galaxies furthest away are moving away faster
  than galaxies closer to us
• We can us Doppler Effect

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Visible Spectrum
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Doppler

• Doppler

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What is Red Shift?

• As light moves away, the waves stretch out
• Longer waves are shifted towards the red
• As light moves towards us, the waves condense
• Shorter waves are shifted towards the blue

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Spectral Signature

• Each element has a unique spectral signature
• Two elements combine

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