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View from a spaceship at relativistic speeds

  1. Oct 17, 2009 #1
    If one was in a spaceship at rest in frame K and sees an evenly-distributed number of stars around them, what would the distribution of stars look like if you were travelling at relativistic speeds (frame K')?

    I'm conflicted because I've seen animations online that seem to illustrate the stars 'bunching up' in front of you (in the direction of motion), but I would think that the starfield would become denser in a ring around the ship and less dense directly in front of you (the direction of motion) and less dense behind you due to length contraction. Below is a simple physical argument:
    if the @ symbol is the spaceship, and the *'s are stars just to the left & right of the direction of motion:
    ..........................................................................................*
    @ -->
    ..........................................................................................*

    As velocity increases, length contraction increases in the direction of travel and the angle between the two stars becomes greater for the observer.
    ..........*
    @ ---------------------->
    ..........*

    So I am not quite sure what actually happens?
     
  2. jcsd
  3. Oct 17, 2009 #2

    JesseM

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    You have to distinguish between what is measured in your frame and what you actually see visually--the second is affected by optical effects like aberration and the Doppler effect, the first is designed to compensate for such effects. Length contraction is what is measured in your frame, but the length in your frame is different from the apparent visual length, because photons from either end of an object that hit your eyes at a single moment were not actually emitted at the same moment in your frame, so the object has moved in between the time light from one end was emitted and the time light from the other end was emitted, which distorts the apparent visual length (see this thread on the Penrose-Terrell effect). Likewise, in the rest frame of a rocket traveler stars do not actually become bunched in front of him (what happens is that the distance between stars becomes contracted in the direction he's moving relative to the stars, though I don't understand why you think this would cause the starfield to become denser in a ring around him), but visually they appear to become bunched in this way due to the visual effect of "aberration"--here are some pages that discuss this:

    http://www.fourmilab.ch/cship/aberration.html (from this more general page on what would be seen by a relativistic traveler: http://www.fourmilab.ch/cship/ )

    http://en.wikipedia.org/wiki/Aberration_of_light

    http://math.ucr.edu/home/baez/physics/Relativity/SR/Spaceship/spaceship.html

    http://www.anu.edu.au/Physics/Savage/TEE/site/tee/learning/aberration/aberration.html

    http://www.relativitybook.com/resources/aberration.html
     
    Last edited by a moderator: Apr 24, 2017
  4. Oct 17, 2009 #3
    JesseM,
    Thanks for the reply, those links helped a lot :)
     
  5. Oct 18, 2009 #4

    A.T.

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