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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 |
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How is it known that the Milky Way is a spiral galaxy ?
"Boo" wrote in message ... 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, 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
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How is it known that the Milky Way is a spiral galaxy ?
Boo wrote in
: 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, It's not only a spiral. It appears to be a barred spiral. http://www.seds.org/Messier/more/mw.html Klazmon. |
#4
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How is it known that the Milky Way is a spiral galaxy ?
OG wrote: "Boo" wrote in message ... 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, 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). I thought that it was determied a spiral by Herschel and his sister..er..er ..Herschel. |
#5
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How is it known that the Milky Way is a spiral galaxy ?
Boo wrote: 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 ? 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
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How is it known that the Milky Way is a spiral galaxy ?
"Weatherlawyer" wrote in message
oups.com... OG wrote: "Boo" wrote in message ... 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, 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). I thought that it was determied a spiral by Herschel and his sister..er..er ..Herschel. 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) |
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How is it known that the Milky Way is a spiral galaxy ?
Mike Dworetsky wrote: I thought that it was determied a spiral by Herschel and his sister..er..er ..Herschel. 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. 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
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OT: Herschel (was: How is it known that the Milky Way is a spiral galaxy ?)
Weatherlawyer wrote:
Herschel and his sister..er..er ..Herschel. 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 -- + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Stephen Tonkin | ATM Resources; Astro-Tutorials; Astro Books + + (N51.162 E0.995) | http://astunit.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + |
#9
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How is it known that the Milky Way is a spiral galaxy ?
Thanks too all for the responses and links.
-- Boo |
#10
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OT: Herschel (was: How is it known that the Milky Way is a spiral galaxy ?)
Stephen Tonkin wrote: Weatherlawyer wrote: Herschel and his sister..er..er ..Herschel. If he was Herschel, surely she was Frauschel? Or may, being anglicised, she was merely Hischel? No, it was him and herschel. |
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