Conference noted::sf

"Relative to what?"

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    re: .2
    
    Thanks!
    
    re: .1
    
    That's a tough question, to which I'm not sure I have a good answer.
    
    But I'll give it a shot.
    
    The motion of the earth within the solar system can be measured
    relative to any thing that is not bound to that motion (Jupiter or
    Alpha Centauri for instance). The motion of Sol through the galaxy can
    be measured in relation to other stars of the galaxy [assuming that all
    of the stars are not moving with the same angular velocity around the
    galactic center], or in relation to stars in other galaxies. The motion
    of our galaxy can be measured relative to other galaxies [again
    assuming that the galaxies are not simply moving around some center,
    all at the same angular velocity].
    
    The motion that comes from universal expansion is the tough one. I
    guess I would like to measure that one relative to the big, black,
    stationary box inside which the universe is expanding. But I'm not
    sure Steve Hawkin (sp?) will let me get away with that. An alternative
    might be to measure the increase in distance between our galaxy and
    another, and then divide by two (or some more appropriate number) to
    account for the fact that the other galaxy is moving as well.
    
    The real goal I'm after is to find out how far we move in a given
    period, how far we are today from where we were on March 21, 1890 for
    instance.
    
    Cheers!
    
    Charlie
    
    P.S. If space really is expanding like the surface of a baloon, and we
         are like dots on that baloon, how we aren't getting farther from
         the moon?

    The point of the question "relative to what" is that there is
    (as far as we know) no absolute standard of rest--that is, there
    is no non-moving point from which you can measure your own
    displacement.
    
    The best approximation to such a standard is the overall average
    of the rest of the Universe (e.g. the "fixed" distant stars and
    galaxies, or the microwave background).
    
    Imagine you are a fish in the deep ocean.  You know you are
    moving relative to other fish, and you want to know how fast you 
    are moving in an absolute sense, and where were you yesterday.
    How would you figure this out?
    
    Well, you might mark the water with a scale, and see how fast
    that scale moved--this gives you speed relative to the "fixed"
    water, but doesn't account for currents (and can't be done in
    space because there's no "water" or friction to slow the scale
    down to the speed of the local space-time continuum, and the 
    scale would be accelerated by the gravity of various bodies
    nearby).
    
    You could take an average of the motions of distant fish, and
    call that zero, but what assurance would you have that it was
    truly zero?
    
    Do you understand why the answer to your question is "this question
    can't be answered"?
    
    			-John Bishop

    Hi John,
    
    I see your point. But I'm not sure that AN answer can't be at least
    approximated. It may not be THE TRUE ANSWER, but then again it might.
    
    We use the doplar shift of light from distant stars to see that they
    are moving away from us, and the farther away they are, the faster they
    seem to be moving away. I like to think that this means we are the
    center of the universe :*). But those pesky astronomers insist that
    space is stretching everywhere and that's why it looks like that.
    Anyhow, if we're moving just like they are moving, we might be able to
    get one component of our speed by finding out their speed. This we
    should be able to do by saying, "How fast would a body have to move to
    produce x-degree of doplar shift?" But this (if it would work) only
    helps with the motion from the stretching of space, which is already a
    tough subject to wrap your head around, and may not be needed for my
    purposes anyway.
    
    The more interesting motion to me, I think, is the galactic rotation.
    I'm not even sure how we know the galaxy is rotating, but if we do, and
    if we know how fast it rotates and how far we are from the center of
    that rotation, we should be able to figger how fast we are moving in
    that respect.
    
    Then there's motion within the solar system which I could probably
    figure out if I took the time, but that motion is too localized for the
    idea I'm working on.
    
    So I guess the issue I'm most interested in is just the question of
    galactic rotation, using the galactic hub as our reference point.
    
    How's that?
    
    Charlie

I have heard the figure of approximatly 60,000 miles per second is our orbit
speed about the center of our galaxy.

Steve

    	Our solar system takes about 250 million years to orbit the
    center of the Milky Way galaxy.  The Milky Way is about 100,000
    light years across.
                
    	I also remember reading in SKY & TELESCOPE several years back
    that there was a theory that the entire Universe rotated, making
    one rotation in 16 trillion years.  I have no idea if this theory
    went any further; besides, the Universe is not scheduled to last
    quite that long anyway.
    
    	Larry
    

    Using the figures from .7 for diameter and orbital time (which, if I
    recall, is correct) we have the following:
    
    Circumference of solar system orbit: 314159 ltyr or 1.8 E18 miles
    
    With a travel time of 250 million years that gives us 7.3 E9 miles per
    year or 234 miles per second (not 60,000 miles per second, which would
    surely cause relatavistic problem being 32%c...)
    
    In fact, a orbital velocity of 60Kmiles/sec would result in a travel
    time around the galaxy of under 1 million years...
    
    jim
    

    Hi Jim,
    
    If you are using the figure of 100,000 ltyr to generate the
    circumference you give, won't that give you the distance traveled by a
    body at the farthest edge of the galaxy? Are we that far out, or is our
    path shorter? Or did you use our distance from the center as a radius?
    
    Also, I'm not familiar with you method of notation. Does 7.3 E9 mean
    7.9 * 10-to-the-ninth or 7.9-to-the-ninth, or something else entirely?
    
    Thanks for the replies everyone,
    
    Cheers!
    
    Charlie

66,000 miles per hour is the Earths velocity in orbit around the Sun. 
234 MPS sounds more like it. for the orbit of the Solar System about the
center of our Galaxy. I remember calculating that sam figure out many years ago.

Steve

    re: .9
    
    the notation "X EY" represents X *10 to the Yth power.  Similar to the
    way it is notated for calculators.  I used 100,000 ltyr for the
    diameter of the orbit of our solar system around the center of the
    galaxy.  Yes we are at the farther reaches fo the galaxys edge, though,
    maybe not that far.  We are located at the far end of one of the spiral
    arms.
    
    If anybody has more accruate information could you do the calculation
    and post the answer?
    
    thanx,
    jim
    

    Values of 100,000, 120,000, and 150,000 have been used by various
    authors in discussing the diameter of the Milky Way.  All, however,
    have generally "agreed" that the Solar System is approximately 2/3 out
    from the galactic center.  The most popular figure I have seen has been
    about 50,000 ly from some hypothetical galactic edge.
    
    Dwight

Enough.  This isn't science fiction.  This topic is closed.

Dave C.
Moderator, whose was negligent in not closing this topic when it was
first entered.