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Thread: Calculating lightspeed with Moon

  1. #1 Calculating lightspeed with Moon 
    Forum Freshman
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    Hello


    The following scientific website http://www.speed-light.info/speed_of...2000.htm#sub_2

    claims that a religious Scripture has foreknolewdged the value of lightspeed.
    (don't put this topic into pseudoscience thread, for I'd only like to discuss the
    scientific reasoning in that website, I don't mind its religious and spiritual aspects
    ).

    It wants to prove that the distance travelled by the Moon (around the Earth) in 1,000 lunar years (according to lunar-based calendars)
    is the same as that of light travelled in 24 hours.



    To calculate lunar distance in 1 000 lunar years:


    they isolate Moon-Earth system from Sun gravitation
    In this case, Earth system doesn't revolve.
    And Moon synodic period become equals to its sideral period
    (thus 1 lunar month becomes=1 sideral period=27days)


    their justifications: The Moon moving around the Earth and around the Sun as well, we cannot take the Earth as a inertial frame of reference, according to the special relativity. Otherwise, the distance calculated would be greater than light distance in 24h. this is why we must isolate Moon-earth system from Sun's gravity for he calculations of Moon's distance.



    What about Moon's speed?



    As we can see, a rotation of Earth-Moon system around the Sun for one synodic month is equivalent to an arc of 27° of the terrestrial orbit around the Sun. This angle (27°) is the same as the angular difference between 1 lunar sideral month and 1 lunar synodic month according to Earth frame of reference.




    The vector "E" (beginning from the Moon) perpendicular to the segment Earth-Sun points to a different direction every synodic month, its module represents the actual Moon's speed (3680km/h)


    Thus from this "triangle" of vectors, can they calculate mean Moon's speed E' in isolated Earth-Moon system:



    E=square root [ (E sin phi)² + (E')² ]

    thus E'= E * cosine phi
    = current Moon's speed * cosine phi
    = 3680km/hour * cosine 27°

    E'=3279 km/hour


    So without Sun's gravitationnal influence on Earth-Moon system, would Moon revolve around the Earth at 3279 km/hour ?
    Could you tell me if their reasonings are right?[/u]


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  3. #2  
    Moderator Moderator Janus's Avatar
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    Their reasoning is BS.

    First off, The Earth-Moon system is in orbit around the Sun and, in effect, is in free fall.
    In other words, the gravitational effect of the Sun on the Moon's orbit is nil (minus a small elongation of the Moon's orbit due to Solar tide). The diagram where they describe the Moon speeding up and slowing down when it moves towards or away from the Sun is completely bogus. The only speeding up and slowing down the Moon does is as it goes from its own perigee and apogee.
    Removing the Sun from the scenario has a negligible effect on the Moon's orbit, and the mean orbital speed would not change significantly.

    Second, their method of calulating the "true" speed of the Moon is complete hogwash. There is no reason for what they did other than to get an answer they could live with.

    If a ancient civilization were to "calculate" the speed of the Moon (given that they knew how far away it was.), they would simply do this: They would note the position of the Moon against the stars and then determine the time it took for the moon to travel through the heavens and return to that point. They would then take that time and divide it into the circumference of the Earth's orbit. Depending on the accuracy of their measurements, they would get an answer of 3680 kph.

    If however they wanted to get and answer based on the synodic month, then they would take the length of the synodic month (full moon to full moon), which is 29.53 days, and divide it into the circumference of the Moon's orbit. This would give a value of 3404.367 kph. Notice how this answer is not the answer they got with their mathematical hocus-pocus.


    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  4. #3  
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    Thanks for your answer, Janus.


    So, in heliocentric frame-reference, Moon's travel in 1 sideral period loos like a curvature (whose distance is called L)



    But this distance L (in heliocentric view) is larger than Moon's orbit circumference (in geocentric view).

    But how about Moon's mean speed relative to the Sun?
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