Earth orbit

Standard memberJigtie
Science 22 Jul '09 06:54
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    22 Jul '09 06:54
    I have a question I debated with a friend who is as inept about physics and mathemagics as meself
    ('twas kinda like reading the RHP socialism vs capitalism debates). We couldn't decide what would
    happen to earth's orbit if the moon were suddenly taken away. Does the moon affect earth orbit
    around the sun (and/or earth rotation around its own axle) to any degree?

    Appreciated if you could keep your LOLs to a minimum. 😳😵
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    22 Jul '09 08:201 edit
    Originally posted by Jigtie
    I have a question I debated with a friend who is as inept about physics and mathemagics as meself
    ('twas kinda like reading the RHP socialism vs capitalism debates). We couldn't decide what would
    happen to earth's orbit if the moon were suddenly taken away. Does the moon affect earth orbit
    around the sun (and/or earth rotation around its own axle) to any degree?

    Appreciated if you could keep your LOLs to a minimum. 😳😵
    Not only does the moon swings go around the Earth but, to a much lesser extent, the Earth “swings” around the moon (although the “swing” is too small for it to appear that way) and this causes the Earth to ‘wobble’ around with the orbit of the moon just as the moon ‘wobbles’ (by a much greater extent such that it appears as an orbit rather than a mere “wobble” ) around with the orbit of the Earth.

    If you where to suddenly take the moon away then there would suddenly be no moon there to maintain that Earth’s lunar ‘wobble’ that was due to the moon and this would effect the Earth’s orbit around the sun (not sure by how much) and exactly how so depend on the exact stage of the lunar cycle the moon was taken away.
  3. Cape Town
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    22 Jul '09 11:05
    Originally posted by Andrew Hamilton
    If you where to suddenly take the moon away then there would suddenly be no moon there to maintain that Earth’s lunar ‘wobble’ that was due to the moon and this would effect the Earth’s orbit around the sun (not sure by how much) and exactly how so depend on the exact stage of the lunar cycle the moon was taken away.
    I doubt that the wobble is particularly significant ie we wouldn't really notice the difference.
    However the tides would stop - a major impact.
    Also - and more important - because the total mass of the earth plus moon would have reduced, the earths orbit around the sun would change dramatically (equivalent to making the earth lighter) causing our years to be longer, our sunlight lower, (and thus our weather colder) and possibly cause an increased chance of collisions with other bodies in the solar system.
    I believe that the moon is also slowing down the earths rotation over time - so that effect would stop but would take a while to be noticeable.
    I also suspect that the moon also helps to stabilize the wobble of our axis, so we might experience increased wobble and which could lead to greater climate change.
  4. Subscribersonhouse
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    22 Jul '09 11:09
    Originally posted by twhitehead
    I doubt that the wobble is particularly significant ie we wouldn't really notice the difference.
    However the tides would stop - a major impact.
    Also - and more important - because the total mass of the earth plus moon would have reduced, the earths orbit around the sun would change dramatically (equivalent to making the earth lighter) causing our years ...[text shortened]... r axis, so we might experience increased wobble and which could lead to greater climate change.
    That last is not a suspect, it is certain. No moon, no stable tilt, chaotic weather.
  5. Cape Town
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    22 Jul '09 13:05
    Originally posted by sonhouse
    That last is not a suspect, it is certain. No moon, no stable tilt, chaotic weather.
    Does mars wobble on its axis more than the earth due to its lack of a moon?
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    22 Jul '09 13:28
    Excellent! Thank you all for answering. I have a follow-up question. This 'wobble' that you speak of,
    is that because the mass of the moon and earth are relatively close in relation to the difference
    between the mass of the sun and earth? I mean, the earth and sun doesn't 'wobble' around each
    other, right?
  7. Subscribersonhouse
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    22 Jul '09 16:41
    Originally posted by twhitehead
    Does mars wobble on its axis more than the earth due to its lack of a moon?
    The tilt of Mars is very chaotic, sometimes the poles face the sun, of course that is on a very long time frame, millions of years. The tilt of Earth has hardly varied in the last billion years by contrast.
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    22 Jul '09 18:182 edits
    Originally posted by sonhouse
    The tilt of Mars is very chaotic, sometimes the poles face the sun, of course that is on a very long time frame, millions of years. The tilt of Earth has hardly varied in the last billion years by contrast.
    Actually the Earth's orbit does wobble the sun -but only by a much smaller amount which would be very hard to detect because the difference in mass between the sun and the Earth is much greater than the difference in mass between the Earth and the moon.
  9. Subscribersonhouse
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    27 Jul '09 22:25
    Originally posted by Andrew Hamilton
    Actually the Earth's orbit does wobble the sun -but only by a much smaller amount which would be very hard to detect because the difference in mass between the sun and the Earth is much greater than the difference in mass between the Earth and the moon.
    Of course. The extra solar planet detectors currently using such doppler shifted movements are not up to detecting earth mass planets at our distance from the sun, as of yet anyway. I expect that to improve in the next ten years as more sensitive probes are launched. I keep waiting for data on Alpha Centauri! Closest star at 4.3 LY out and a triple bonus, three stars for the price of one star trip! Such a deal!
  10. Cape Town
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    28 Jul '09 11:43
    Originally posted by Jigtie
    Excellent! Thank you all for answering. I have a follow-up question. This 'wobble' that you speak of,
    is that because the mass of the moon and earth are relatively close in relation to the difference
    between the mass of the sun and earth? I mean, the earth and sun doesn't 'wobble' around each
    other, right?
    We are talking about the movement of the rotational axis of the earth or mars. The moon pulls on the earth and so keeps its rotational axis more or less perpendicular to the moons orbit. For the earths rotational axis to move significantly, the orbit of the moon would have to move too.
    I am sure that the planets in general also exert some stabilization on the suns rotation, but as pointed out by others it might be insignificant. Certainly it would be dominated by Jupiter.
  11. Cape Town
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    28 Jul '09 11:45
    Originally posted by sonhouse
    Of course. The extra solar planet detectors currently using such doppler shifted movements are not up to detecting earth mass planets at our distance from the sun, as of yet anyway. I expect that to improve in the next ten years as more sensitive probes are launched. I keep waiting for data on Alpha Centauri! Closest star at 4.3 LY out and a triple bonus, three stars for the price of one star trip! Such a deal!
    Actual movement of the sun around the centre of mass of the solar system is not quite the same as wobble in the axis tilt.
    Does anyone know how far off the Earths axis the centre of mass of the earth - moon system is (and therefore how much shift the earth goes through for each moon cycle?
  12. Subscribersonhouse
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    29 Jul '09 22:12
    Originally posted by twhitehead
    Actual movement of the sun around the centre of mass of the solar system is not quite the same as wobble in the axis tilt.
    Does anyone know how far off the Earths axis the centre of mass of the earth - moon system is (and therefore how much shift the earth goes through for each moon cycle?
    Here is a link to the eccentricities in the Earth's orbit, but I didn't see the one about how the moon effects the yearly orbit of earth.
    http://www.gateway-to-the-universe.org/brent/tourist/earth0.htm
  13. Standard membersven1000
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    30 Jul '09 00:37
    Originally posted by twhitehead
    Actual movement of the sun around the centre of mass of the solar system is not quite the same as wobble in the axis tilt.
    Does anyone know how far off the Earths axis the centre of mass of the earth - moon system is (and therefore how much shift the earth goes through for each moon cycle?
    It should be a simple ratio of their masses.
    m_earth * r_earth = m_moon * r_moon
    where the m is for mass and the r for distance from center of object to center of mass of the system. So if the earth is 80 times more mass, then the distance between the center of the earth and the center of the earth-moon system is ~1/81 the distance between the center of the earth and the moon.
    The earth-moon distance is ~400,000 km, so the distance between the center of the earth and the center of mass is ~5,000 km, nearly the radius of the earth.
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