Measuring the Distance to Stars

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Measuring the Distance to Stars
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The Parallax Method

• To the naked eye stars are so far away that they
  do not appear to change positions even though we
  are rotating (8,000 miles wide) and revolving
  (186, 000,000 miles).
• However with the invention of photography, we had
  new tool to record stars and look for tiny shifts
  in their position

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The Parallax Method

• The first time we were able to see a tiny shift
  in the position of a star was in 1916 during the
  First World War.
• The shifts are less than an arcminute and were
  only possible because of the improvements of
  photography and telescopes.

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The Parallax Method
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The Parallax Method

• We use the orbit of the Earth to make our
  measurements.
• By taking pictures 6 months apart we have moved
  about 186,000,000 miles.
• This change of position makes the nearby stars
  appear to shift compared to the more distant
  stars.
• By recording the angle of the shift we can
  calculate the distance to the star.

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The Parallax Method

• For very small angles we can assume that the sine
  of the angle is very close to the value of the
  angle itself (using radians as the measure).
• Therefore Sin ? opp/hyp and
• Hyp opp/sin ? or Hyp opp/ ?

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The Parallax Method

• However, to simplify things astronomer have
  developed an easier formula based on the parsec.
• 1 parsec 3.26 light year, where
• 1 light year 5.88 trillion miles
• The formula is d 1/p where d is distance in
  parsecs and p is the parallax measured in arc
  seconds.

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The Parallax Method
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