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Integrated Coordinated Science for the 21st Century

Active Physics
+ Chapter 6
Is Anyone Out There?
Answers
Physics To Go
  1. a) Parallax is the apparent shift in position of an object when the object is seen from two different places.
    b) Because the point of view has shifted.
    c) Because the apparent position shifts less as the distance to the object increases; if you face a distant tree and take a step to the right, you are still facing the tree.
    d) The shift is so small it cannot be measured.
    e) The astronomer observes the shift against the background of the much more distant stars.
  2. a) A perpendicular change makes the shift large, because it produces the largest change in the direction of the object, as seen by the observer.
    b) A parallel shift produces no shift, because the direction of the object, as seen by the observer, does not change.
  3. a-b) The pencil’s position seems to shift.
    c) See drawing on page 336.
    d) With both eyes you can see depth.
    e) The amount of the shift would be less.
  4. a) 10 cm
    b-d)
    Parallax

    e) The longer the distance, the smaller the shift in the angle in sighting from one end of the baseline or the other.
  5. a) Yes b-d) It was easier with both eyes open, since both eyes sense depth. Depth perception works because each eye has a different view of the object, due to parallax.
  6. a) Call N the number of seconds in a year. Approximately, N = 12 months/year X 31 days/month X 24 hours/day X 60 minutes/hour X 60 seconds/minute = 3.2 X 107 s. Number of miles in a light-year = c X N = 6.0 X 1012 mi.
    b) 1.2 X 1012 hours
    c) 9.6 X 1015 meters