Newbie questions about our galaxy

[someone_else]

Sorry, I am still new here and I don't know too much about Astronomy (although I LOVE it!) so forgive my nescient questions...<br /><br />If we are inside the Milky Way galaxy, and everything is so far away, how can we tell that we are in a spiral galaxy? How can we tell what position we occupy in one of the arms? How do we even know where the center of the galaxy is? How would we know where to look?<br />

 

[raghara2]

There is a really big radiation in the center so it's quite easy. Rest of it is guessing compared with other galaxies.

 

[yevaud]

Dang. Just beat me to it.<br /><br />By measuring the distance to nearby stars, and working out towards the distant one's, using a variety of means of measurements (red shift, cepheid variables, etc.), we've worked out a good idea as to the shape of the Milky Way. And Galaxies usually fall into one of several shapes: spiral, elliptical and so on.<br /><br />And, yes, RagharA2 is correct. We can see the very bright, very energetic center of the Milky Way galaxy (known as the "Shapely" Center). <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[someone_else]

Thank you for the reply, but surely there must be more to it than that?

 

[odysseus145]

If you look up on a dark night, you'll notice what appears to be a band of stars streching across the sky. This tells us that the milky way is a disc. That and the energetic center make it pretty clear that the Milky Way is a spiral. <div class="Discussion_UserSignature"> </div>

 

[yevaud]

Yes. The band of stars you see that is the Milky Way, is the plane of the Galaxy. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[vogon13]

Plotting the locations of all the milky ways globular clusters reveal them to be arranged roughly spherically around a point ~30000 light years away in the dirction of (IIRC) Sagitarius.<br /><br />When we look at other galaxies, we note their globular clusters are located roughly spherically about the centers of their visible disks (in the case of spirals). <br /><br />IIRC, an astronomer named Harlow Shapley put this all together ~80 years ago. <br /><br /> Seems likely we have our own galaxy figured out, ie. that the center of our galaxy is ~30000 light years away in the afore mentioned constellation. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[someone_else]

Thank you all for your copious responses...<br /><br />How do you know which bright energetic spot is the center of the Milky Way? How would you even know which direction to look in?

 

[Saiph]

it's actually a pretty complicated question that's taken a long, long time to discern with any real accuracy.<br /><br />First, the fact that we are in a galaxy that is primarily a plane is easy to determine, merely look at the overall distribution of stars.<br /><br />With good optics, and thurough surveys, its easy to determine that we can look further in one direction along the disk, than the others, thus indicating we are near an edge. We can look further in that direction, because we get to the edge, and have no more material to block our view. In the opposite directions, we have to wade through lots of stuff.<br /><br />By observing the motions of stars relative to eachother, and the motions of globular clusters, we can begin to discern a center of the galaxy.<br /><br />Most disk galaxies are spirals, and spiral arms have various properties (O and B class stars, denser hyrodgen contents, etc) and by mapping out the locations of these properties, we can map out the spiral arms (quite imprecisely I might add). <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[someone_else]

Wow...this really is fascinating. Thanks all for your responses.