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Homework Help: Relativity, time difference from two planets

  1. Apr 16, 2013 #1
    1. The problem statement, all variables and given/known data
    Two planets A and B have relative velocities 0.7c.
    They can observe the birth of two stars, C and D.
    According to planet A, star D was born 10 years before star C was born.
    According to planet B, star C was born 20 lightyears farther than star D.
    What is the time difference between the birth of the stars in the reference frame of planet B.

    The attempt at a solution
    S: Planet A
    S': Planet B

    β=0.7 → γ=1.4


    I assume this is incorrect.
    I am really struggling with relativity, and my textbook only has a short section which doesn't explain too much. Any help will be appreciated.
  2. jcsd
  3. Apr 17, 2013 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Because the time period ended up negative?
    Apart from that I cannot see what you did - you appear to have plugged some unspecified numbers into an equation.
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