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What do We Orbit? - Astronomy Expert Needed.

  • 17-04-2010 12:01am
    #1
    FISMA
    Closed Accounts Posts: 2,616 ✭✭✭


    Somewhere in the back of my mind I think I remember a discussion with a Dr of Astronomy that is now causing confusion.

    Anyhow, true, the Earth orbits around the solar system's center of mass which is located within the Sun.

    Gravity is believed to be limited by the speed of light, blah, blah, blah...

    Example: if the Sun vanished right now, the Earth would continue to "orbit" for over 7 minutes and then go tangent to the curve at the point where we last saw sun light.

    That's the weird part.

    We conclude that we orbit where the sun WAS and not where the sun IS?

    However, I would have sworn that the Doctor quoted data that showed the Earth orbits where the Sun IS and not where it WAS.

    Has anyone any information, a link, a study, a reference to an experiment to show either case?

    Thanks


Comments

  • #2
    The Hill Billy
    Registered Users, Registered Users 2 Posts: 22,818 ✭✭✭✭The Hill Billy


    Brilliant question. Afraid I haven't a clue myself, but looking forward to any answers.


  • #3
    Beeker
    Moderators, Science, Health & Environment Moderators Posts: 3,645 Mod ✭✭✭✭Beeker


    FISMA wrote: »
    Somewhere in the back of my mind I think I remember a discussion with a Dr of Astronomy that is now causing confusion.

    Anyhow, true, the Earth orbits around the solar system's center of mass which is located within the Sun.

    Gravity is believed to be limited by the speed of light, blah, blah, blah...

    Example: if the Sun vanished right now, the Earth would continue to "orbit" for over 7 minutes and then go tangent to the curve at the point where we last saw sun light.

    That's the weird part.

    We conclude that we orbit where the sun WAS and not where the sun IS?

    However, I would have sworn that the Doctor quoted data that showed the Earth orbits where the Sun IS and not where it WAS.

    Has anyone any information, a link, a study, a reference to an experiment to show either case?

    Thanks
    No expert here but my understanding is the the Earth continues to orbit where the Sun "was" because the information about the suns non existence can only move out to the earth at the speed of light. So it the sun were to vanish from our universe we would continue to see it and feel its heat and gravity for 8 minutes. Gravity moves at the speed of light so its pull or "suck" moves out from its sourse at the speed of light.

    Not sure if that is what you are after but hopefully someone smarter will come along with a better explanation:)


  • #4
    djhaxman
    Registered Users, Registered Users 2 Posts: 1,351 ✭✭✭djhaxman


    Gravity moves at the speed of light? Eh?


  • #5
    Beeker
    Moderators, Science, Health & Environment Moderators Posts: 3,645 Mod ✭✭✭✭Beeker


    djhaxman wrote: »
    Gravity moves at the speed of light? Eh?
    The "effect" of gravity moves at the speed of light. Or am I missing something:confused:


  • #6
    Conor108
    Registered Users, Registered Users 2 Posts: 3,871 ✭✭✭Conor108


    According to Wikipedia -
    The speed of gravity in general theory of relativity is equal to the speed of light in vacuum, c


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  • #7
    Kevster
    Closed Accounts Posts: 2,980 ✭✭✭Kevster


    djhaxman wrote: »
    Gravity moves at the speed of light? Eh?
    That's the answer I would have given. It's the only answer that I feel is needed for this question. it's the same for other celestial bodies too, such as the moon, for example. If it vanished, we'd still feel its effects on the tides and such for a few seconds.


  • #8
    thecommander
    Registered Users, Registered Users 2 Posts: 2,537 ✭✭✭thecommander


    Newtonian models says its instantaneous

    General relativity says its at the speed of light.

    Sounds like grounds for a fight tbh.

    Link


  • #9
    mike65
    Closed Accounts Posts: 88,972 ✭✭✭✭mike65


    Nah here's the fight ;)


  • #10
    Sykk
    Closed Accounts Posts: 3,327 ✭✭✭Sykk


    From my understanding gravity does infact move at the speed of light. I'm pretty sure this cockblock was the cause of the development for the space/time theory.. I may be wrong it's been a while since I read it.


  • #11
    eightyfish
    Registered Users, Registered Users 2 Posts: 2,100 ✭✭✭eightyfish


    Information can't move faster than the speed of light. This includes electromagnetic fields, forces like gravity and also energy (light). In fact most things without mass can move at this speed. So the effect of gravity can only move at the speed of light, as this is the highest speed possible.

    The only information that can move faster than light is that shared between entangled particles, but that's getting into quantum mechanics which really is so complicated it could ruin your morning.

    AFAIK, anyway.


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  • #12
    Sykk
    Closed Accounts Posts: 3,327 ✭✭✭Sykk


    eightyfish wrote: »
    Information can't move faster than the speed of light.
    The rest of the speech was kinda irrelevant as nothing can move faster. We're talking about it being slightly behind/on par


  • #13
    Mr Amazing 2
    Closed Accounts Posts: 8 ✭Mr Amazing 2


    No No No! that's just wrong.....my head hurts ouch ouch.

    Ok here's the twice.

    If two stars were traveling parrellel in the same direction at near the speed of light. they would no longer feel the effect of each other's gravity as their gravities would be behind them :eek:.

    Fluid Dynamics; Zone of silence ? ??


  • #14
    eightyfish
    Registered Users, Registered Users 2 Posts: 2,100 ✭✭✭eightyfish


    Mr Amazing 2 wrote: »
    If two stars were traveling parrellel in the same direction at near the speed of light. they would no longer feel the effect of each other's gravity as their gravities would be behind them :eek:.

    The stars are not moving relative to each other so that should not affect garvity.


  • #15
    Sykk
    Closed Accounts Posts: 3,327 ✭✭✭Sykk


    Mr Amazing 2 wrote: »
    No No No! that's just wrong.....my head hurts ouch ouch.

    Ok here's the twice.

    If two stars were traveling parrellel in the same direction at near the speed of light. they would no longer feel the effect of each other's gravity as their gravities would be behind them :eek:.

    Fluid Dynamics; Zone of silence ? ??
    It's nowhere near possible that 2 stars can travel even 1/100000th of that speed. So your playing with a mindfook there my friend.

    That's like the "If we could move faster than the speed of light and went to mars, we could see ourselves get there"


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