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Varying timing of eclipses of Algol and constant speed of light?

  1. Feb 22, 2009 #1
    Take a look...

    Now then, if light always passes us at the same speed then what is causing the decrease in time between eclipses when we are moving towards Algol and an increase in time between eclipses when we are moving away from Algol?
  2. jcsd
  3. Feb 22, 2009 #2


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    It's not the moving per se, but the fact that you are closer or further away. The key bits from the link you provided are:

    "So in 2.867321 days the Earth moves about 7,379,039 km closer to Algol."

    "its light waves left Algol 93 years ago and are travelling at a constant speed."

    "7,379,039 km divided by the speed of light 299,792.458 km/sec is 24.61382 seconds"

    "this rough calculation explains the deviations we see in Graph 2"
  4. Feb 23, 2009 #3
    Hmmm...Nobody is willing to admit that which is plainly obvious. Namely, that we have empirical evidence that the speed of light is not constant relative to all observers. If you have cars traveling towards you at a constant speed and they are equally spaced apart and you increase your velocity in the direction opposite to their movement (i.e. run towards them), then the time between each car is decreased and the cars' velocity relative to you is increased. So, another way of stating this is...
    Last edited: Feb 23, 2009
  5. Feb 23, 2009 #4


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    Everything is worked in a single frame.

    The hypothesis of varying speed of light must be tested by comparing measurements in different frames.
  6. Feb 23, 2009 #5

    D H

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    Do not put words in people's mouths.

    Your substitution of constant speed with constant speed relative to the aether is (a) not justified, (b) not needed to explain the phenomena, and (c) does not explain the phenomena. You need to justify why you think the way do. Putting words in other people's mouths (or writing in this case) does not cut it.
  7. Feb 24, 2009 #6
    I put that in there because it is clearly understood. Notice that it doesn't say..."the light from Algol slows down when we are heading towards it and speeds up when we are heading away from it in order to maintain a constant speed of c for the observers on the Earth."

    I would like to point out something. Let us assume for a moment that SR is true and Algol is let's say 100.5 light-years away. Now then, if SR is true then the time required for light from emission to reception merely depends on the distance at the time of emission. Let's say that the Earth is closest to Algol in its orbit and there is an eclipse. Now then, the eclipse will arrive on Earth after Earth has made 100.5 orbits around the Sun. But after 100.5 orbits, the Earth is furthest away from Algol in its orbit. So the eclipses that occurred when the Earth was receding from Algol will start arriving on Earth as the Earth is approaching Algol. So we would have the bizarre effect of the eclipses being further apart in time as we are approaching Algol.
  8. Feb 24, 2009 #7


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    The time required for light to arrive depends on the location of the emitter at the time of emission and the location of the receiver at the time of reception.

    The speed of light is constant in two senses:
    (i) within one inertial frame in vacuum, the speed of light does not change over time.
    (ii) in a frame moving at constant velocity relative to an inertial frame, the speed of light is the same as in the inertial frame.

    In this example, sense (i) is being used; sense (ii) is not used since everything is worked in a single frame.
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