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  1. #1
    Boo's Avatar
    Boo Guest

    Default How is it known that the Milky Way is a spiral galaxy ?



    Hi,

    The question is as the title : given that we see it edge on, then how is it
    known that the Milky Way is a spiral galaxy with arms and all ?

    Thanks,

    --
    Boo

  2. #2
    OG's Avatar
    OG Guest

    Default How is it known that the Milky Way is a spiral galaxy ?


    "Boo" <reply_to_group_not_me@spam_me_no_spam.net> wrote in message
    news:JYGdnXW05cD5gebZRVn-rw@biscit.net...

    The first evidence was provided by Radio astronomy, where radio observations
    of atomic Hydrogen wavelengths showed the existence of large scale
    structures that could be interpreted as arms. (a rotating disk model allows
    us to determine where a body of gas is placed by measuring its relative
    speed to us).

    Later observations for radio emissions for other atoms provided stronger
    evidence for 'arms', but there were continuing problems in determining the
    distances to these large scale features within the galaxy.

    Correlating optical observations of 'young' features and radio observations
    gave stronger evidence of spiral structure.

    http://www.cfa.harvard.edu/~reid/background.html

    As is usual, the accepted model of the Milky Way is based on a number of
    strands of evidence that contribute towards a consistent model.



  3. #3
    Llanzlan Klazmon's Avatar
    Llanzlan Klazmon Guest

    Default How is it known that the Milky Way is a spiral galaxy ?

    Boo <reply_to_group_not_me@spam_me_no_spam.net> wrote in
    news:JYGdnXW05cD5gebZRVn-rw@biscit.net:


    It's not only a spiral. It appears to be a barred spiral.

    http://www.seds.org/Messier/more/mw.html

    Klazmon.

  4. #4
    Weatherlawyer's Avatar
    Weatherlawyer Guest

    Default How is it known that the Milky Way is a spiral galaxy ?


    OG wrote:

    I thought that it was determied a spiral by Herschel and his
    sister..er..er ..Herschel.


  5. #5
    Martin Brown's Avatar
    Martin Brown Guest

    Default How is it known that the Milky Way is a spiral galaxy ?


    Boo wrote:


    The most convincing direct observations are from radio astronomy using
    spectroscopy of the neutral hydrogen 21cm spectral line. The amount of
    material and its velocity can be deduced along a line of sight. A
    short reasonably accessible intro is online at:

    http://homepage.smc.edu/balm_simon/f...milky_way.html

    Regards,
    Martin Brown


  6. #6
    Mike Dworetsky's Avatar
    Mike Dworetsky Guest

    Default How is it known that the Milky Way is a spiral galaxy ?

    "Weatherlawyer" <Weatherlawyer@hotmail.com> wrote in message
    news:1148954926.394261.299770@u72g2000cwu.googlegr oups.com...
    how is
    observations
    allows

    Caroline. No, William Herschel determined by star counts that our star
    system was somewhat flattened, and a few thousand light years* across, but
    he was not able to determine anything about spiral structure. Lord Rosse
    was the first to observe spiral structure visually in an external galaxy,
    M51, at least half a century after Wm. Herschel. But at that time the true
    nature of nebulae was unknown.

    The Milky Way was widely believed to be a spiral by analogy with external
    galaxies before the radio astronomy result, but only after Hubble's
    discovery of the true distance to nearby galaxies.

    *The underestimate was due in part to not realising the importance of
    interstellar dust in obscuring the view of distant stars.


    --
    Mike Dworetsky

    (Remove "pants" spamblock to send e-mail)


  7. #7
    Weatherlawyer's Avatar
    Weatherlawyer Guest

    Default How is it known that the Milky Way is a spiral galaxy ?


    Mike Dworetsky wrote:

    It strikes me that we still don't know all we think we do about our
    home despite all the theories. We don't know for a fact what is at the
    heart of the sun never mind nebulae.

    When god parted the waters, was this space dust a layer of the watery
    deep? God knows. No man alive can say at any rate. The only thing we
    can say for certain apparently, is that we still don't have a parallax
    on any of the stars yet.


  8. #8
    Stephen Tonkin's Avatar
    Stephen Tonkin Guest

    Default OT: Herschel (was: How is it known that the Milky Way is a spiral galaxy ?)

    Weatherlawyer <Weatherlawyer@hotmail.com> wrote:

    If he was Herschel, surely she was Frauschel? Or may, being anglicised,
    she was merely Hischel?

    I'll get me coat....

    Best,
    Stephen

    Remove footfrommouth to reply

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  9. #9
    Boo's Avatar
    Boo Guest

    Default How is it known that the Milky Way is a spiral galaxy ?

    Thanks too all for the responses and links.

    --
    Boo

  10. #10
    Weatherlawyer's Avatar
    Weatherlawyer Guest

    Default OT: Herschel (was: How is it known that the Milky Way is a spiral galaxy ?)


    Stephen Tonkin wrote:

    No, it was him and herschel.


 

 
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