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Do all stars have same revolving speed?

  1. Apr 29, 2012 #1
    In our milky way, do all stars have same revolving speed? This Question is in my mind because we always sees that all star are always in same position with respect to other, i mean if take an example of orion constellation then it seems that betalgeous is always in a same position with respect to rigel. so betalgeous, rigel or any other star in our galaxy have same revolving speed?
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  3. Apr 29, 2012 #2
    Stars do seem to revolve at similar linear speeds (and therefore different angular speeds), but the reason you see these stars appearing fixed in the sky is that the rotation speeds are so slow, and the distances so far, that during any one person's lifetime you could not notice the change in the location of the stars.
  4. Apr 29, 2012 #3

    D H

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    Barnard's star:


    The above is an animated gif that displays the proper motion of Barnard's star from 1991 to 2007.
  5. Apr 29, 2012 #4
    Barnard's star is incredibly close to our solar system, in astronomical terms. Rigel and Betelgeuse are over a hundred times farther away than that, so the change to their relative position on the sky is minuscule.
  6. Apr 29, 2012 #5
    So after many million year we may see stars in anyother position? I mean they leave their respective constellation?
  7. Apr 29, 2012 #6
    Yeah, I've wondered about the orbits of stars, on a relative astronomical scale, near us too.

    Since I have generally no astronomy knowledge, I've always treated stars in our galaxy similar to how we treat planets in our solar system. You could go one level further down in my dichotomy for the orbit of moons around planets. So, naively, everything is just orbiting on different astronomical scales. Our galaxy is spinning around a black hole (like our planet has angular momentum around our star), so I'd think there would be similarities of our star's orbit with respect to other stars near us (I guess maybe aside from Barnard's star). I don't know, my physics knowledge is more earthly, so anyone feel free to correct me if the view is too naive.
  8. Apr 29, 2012 #7


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    Here's an animation that shows the how the Big Dipper changes from 100,000 BC to 100,000 AD.

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    • uma.gif
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  9. Apr 30, 2012 #8
  10. Apr 30, 2012 #9


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    Well, the inner part of our solar system (with the planets) has a lot more order than the galaxy. In our solar system, the sun has something like ~99% of the total mass and everything orbits the sun.
    The galaxy gets its mass mainly from all the stars and gas flying around, which is not a nice (nearly) point-like source like the sun. Therefore, the motion of the stars on a galactic scale is much more complicated, many of them don't have nice orbits as the planets do. And even if they do, the orbits of stars near them can be different (something like ~20km/s of random motion, compared to the orbital velocity of ~200km/s for stars near the sun).
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