title: Finding periods of a plot
body: <p>I've constructed a figure containing 3 different plots representing a position of 3 different masses over some time range. I want to find the period of each. I'm not familiar with the FFT function that I've come across while searching for ways to find the period online. How do I go about this?
  Below is the kernel for the plot and the figure; I won't include the code used to build all these variables as it would be quite extensive.</p>
  
  <p>I know I code just start making vertical lines and then estimate by eye, but I'd much rather do it through coding than with that method.</p>
  
  <pre><code>#using the times in days
  T9 = 500
  dt9 = 0.5
  num9 = T9/dt9
  times9 = np.linspace(0, T9, num9)
  xpos_q9_m1_AU_new = xpos_q9_m1_AU[:-1]
  xpos_q9_m2_AU_new = xpos_q9_m2_AU[:-1]
  xpos_q9_m3_AU_new = xpos_q9_m3_AU[:-1]
  plt.plot(times9, xpos_q9_m1_AU_new)
  plt.plot(times9, xpos_q9_m2_AU_new)
  plt.plot(times9, xpos_q9_m3_AU_new)
  plt.xlabel('Time (days)')
  plt.ylabel('X Positions (AU)')
  plt.title('X Position of the Kepler 16 System over Time')
  plt.legend(['Body 1', 'Body 2', 'Body 3'])
  plt.savefig('q9_plot.png');
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/nv2nv.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nv2nv.png" alt="X Position of Masses over Time"></a></p>