Space Exploration Project

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Space Exploration Project

• Light-years ,Triangulation and
• Parallax
• By Fang Ming Zhang

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AU

• Astronomical units (AUs) , are used to
  measure distances in the solar system . The AU
  ,based on the distance between Earth and the Sun
  ,is equal to 150 million km.

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Light-years

• As the distances to most stars from Earth
  are in billions of AUs ,astronomers have devised
  a different unit to talk about the enormous
  distances outside our solar system .That unit is
  called a light-year .

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• A light-year is the distance that light ,
  which moves at 300 000 km/s ,travels in a year
  .It is equal to about 9.5 trillion km.

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Techniques for Indirectly Measuring Distance

• Telescopes cannot directly determine the
  distance to objects in space . It is also not
  possible to physically measure such long
  distances . For these reasons , two such
  techniques have been used for thousands of years
  to determine distances on Earth
• Triangulation and parallax .

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Triangulation

Imagine you are standing at the side of a lake
and can see a small island in the distance . If
you cannot reach the island , you have no way of
directly measuring how far it is from where you
are.The same problem confronts astronomers but on
a far greater scale.
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• Suppose point A is the position of Earth in
  January , point B is the position of Earth in
  June , point C is a nearby star . we need to
  measure the distance from point C to line AB .

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• There is a solution. We need measure angle
  1 and angle 2 . Then construct a scale drawing
  and draw a perpendicular line between baseline AB
  and C on the scale drawing . Measure the length
  of CD , and then calculate the actual distance
  according to the scale of the drawing. Then we
  will know how far the star C from AB is.

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Parallax

• Try this extend your arm and hold up
  your thumb . As you look with your left eye only
  , line your thumb up against an object on the far
  wall , such as light switch or the corner of
  window . Without moving your thumb , now look
  with your right eye only . The apparent shift of
  your thumb against the stationary background is
  called parallax .

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The end