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About how far are we now from where we were one year ago?

  1. Aug 11, 2009 #1
    NOT the total distance that we have traveled, straight, curved, or whatever, through space but how far are we now, direct line, from where we were a year ago, say within 10% or so? I understand that there are a few motion items involved with this but I am looking for an approximation only. Just using our Sun's speed through space ends up saying that the distance is NOT all that great, by my calc.
     
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  3. Aug 11, 2009 #2

    Pengwuino

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    Relative to what? :biggrin:
     
  4. Aug 12, 2009 #3

    Nabeshin

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    This reminds me of a rather long-winded discussion we had around here a bit back about trying to calculate the velocity of the Earth accounting for all factors, and I really hope it doesn't go in that direction.

    Relative to the sun we've moved nothing, relative to the galactic center, a bit.
     
  5. Aug 12, 2009 #4

    marcus

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    What do you have for the sun's speed? The figure I have is about 370 km/second in the general direction of the constellation Leo---this being motion relative to the cosmic microwave background.

    I'm not being exact about the figure. It is about 1.25 thousandths of the speed of light.
    So in a year the solar system would have traveled about 1.25 thousandths of a light year.

    Or if you want it in kilometers, multiply 370 kilometers by the number of seconds in a year.
     
  6. Aug 12, 2009 #5
    I had 11 Miles per sec. for the Sun's speed. Using your info. I calc. that we travel about seven and a quarter Billion miles in one year. (86,400 X 365 X 229.4) This seems somewhat substantial. Thanks for your reply.
     
  7. Aug 12, 2009 #6

    marcus

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    Sure. I don't remember the precise figure but it is around 370-380 km/s.

    You can use the Google calculator to make it easy. Type this into the regular search window:

    "1 year*370 km/s"

    It will say 1.17 x 1013 meters. You can easily see that is 1.17 x 1010 kilometers. This is 11.7 billion kilometers.

    But the google calculator (which lives in the regular google search box) will also help you convert to miles. You can type in
    "1 year*370 km/s in miles"

    and it will immediately say 7.26 billion miles. So it more or less agrees with what you got.
    =========

    The speed of around 370 was published sometime around 2002 or so by the COBE team, they were the main study of the Background before WMAP began giving data.
    That is the speed of the solar system relative to the cosmic microwave background, as determined by the doppler hotspot which we see ahead of us. The background is slightly warmer ahead, in the Leo direction, than it is on average overall. And it is slightly colder behind us, for the same doppler reason.

    The Background is the light from the ancient matter of the universe and the best reference for determining overall motion.

    One can also talk about our galaxy's motion relative to background. If I remember something in the range 500-600 km/s towards the southern constellation of Crater (near Hydra-centaurus but not exactly, more accurately Crater).
    And one can talk about the suns or the solarsystems motion in its orbit around galaxy center. It is moving some 250 km/s relative to Milky center. And these are not in the same direction so there is some partial cancelation and the upshot is the 370 km/s.
    When we make observations of the rest of the universe it is this 370 km/s motion that has to be eliminated from the data, that we have to correct for in other words.

    The COBE paper was by Charles Bennett et al. as I recall. It is the authoritative source on this, I think. If anybody knows a more recent source, like from WMAP, I would like to know.
     
  8. Aug 13, 2009 #7

    Chronos

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    Measurements from within the solar system are irrelevant.
     
  9. Sep 2, 2009 #8
    and more or less canceled by the one year period

    we have solar motion + milky ways motion + local group motion
    then our overly pickie mods stifle any further thoughts on motions

    but it is a very basic human question
    where were we
    where are we now
    and where are we going
    how fast are we moving
    and what direction are we moving

    if you want a point to measure from how about the so called great attractor
    or pick a bright quasar far far away
    the basic question remain how fast and what direction
     
    Last edited: Sep 2, 2009
  10. Sep 2, 2009 #9

    marcus

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    That's what we were talking about earlier. If you add all the motions as vectors you get 370 km/s in the direction of Leo.

    I didn't hear any "pickie mods" cutting off discussion.

    Are you asking that question?
    Let me answer again.
    Take the velocity of solar system wrt galactic center
    add the motion of the milkyway galactic center wrt local group
    and add the motion of the local group wrt to the cmb background

    then you get the solar system motion wrt background (with respect to the light from ancient matter).

    That velocity (speed and direction) was measured very accurately by COBE and the paper was published some 10 or 12 years ago.
    They gave the coordinates and it turned out to be about 370 km/s in the direction of constellation Leo.

    If you want to hunt down the paper ...
    well this is not the best maybe but I have to go.
    http://arxiv.org/abs/astro-ph/9601067

    This says monopole 2.725 K and dipole 3.353 mK in the direction given by right ascension 11 hours 12 minutes declination -7.1 degrees. Which works out to 368.8 km/s (which we can round to 370) in the direction I mentioned. The authors were the top experts on this at the time. One got Nobel.
    I don't think the estimates have changed significantly.

    I checked and you were asking the same question 2 and 1/2 years ago, Feb 2007.
    Got same answer. Broken record-type vicTroll-a?
    https://www.physicsforums.com/showthread.php?p=1232466#post1232466
     
    Last edited: Sep 2, 2009
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