How can we tell what the Milky Way Galaxy looks like, if we are inside it?

Answer 1

We couldn't tell until the advent of radio astronomy in the 1950s. At that time it became clear that we are in a spiral galaxy, ~2/3 out from the center. We are actually between two great spiral arms, which have been named "The Sagitarius arm" which lies immediately between us and the center of the galaxy, and "The Perseus Arm" which lies between us and the outer edge. Some have tried to say that we are in an arm also, which they have tried to call "The Orion Arm" but most experts agree that there is no such Orion arm, and the reality is that we are just floating along in the gap between spiral arms. The only way to really see what our galaxy looks like from the outside would be to send a probe ~100,000 light years or more away from us and then have it send back pictures. Or else we could contact an alien civilization in a nearby galaxy and they could send us pictures. But such a transmission from the Andromeda galaxy, for instance, would take 2 1/2 million years to get to us, one way.

Answer 2

Well its a guess. Not long ago they changed their minds and now think we are probably a barred spiral instead of just a spiral.

We can tell many things by observing our galaxy an comparing what we see inside our galaxy to what we know other galaxies look like. We can tell by our flat shape we are not an eliptical galaxy, we also can see by looking at our flat shape we are not an irregular galaxy. This means we must be a spiral galaxy. As for how many arms, we can see three of them plainly using diffent methods. By looking at star colors, knowing that this color is produced by a star that is of a certain magnitude and size we can then conclude how far these stars are from us. By using this information we can then see how the stars "clump" together to form the arms. Then by using differnt types of telescopes such as infra red telescopes, and radio telescopes we can see further then white light telescopes have allowed use to see, so we get an even large "picture" of what is around us and a better pproximation of the shape of the part of the galaxy we can see. Beyond that we can interpuate the how many total arms we have. The barred spiral has come out of the density of the stars in the galatic core...from what I understand the core seeme sto be more dense then we thought before and this could only be caused by a barred center.

So while we can not see what our galaxy looks like from the outside, by observing differnt galaxies and then using what we can see of our own, astronomers can draw a fairly close approximation.

Answer 3

we can't really- but we can take an educated guess based on the distrubution of stars that we can see- and all indications fit that of a spiral galaxy.

You must live in a city, and don't get to look up and see the Milky Way stretching across the sky. As we're about 2/3 of the way out on an arm, you can pretty much see the galaxy from where we're at.

Answer 4

Infrared (IR) star surveys and IR spectroscopy (IR penetrates the shrouding dust between us the center of the galaxy) giving us the radial motions of the stars have given us a decent picture of the galaxy. Radio/microwave surveys of molecular gas and neutral hydrogen have also given hints, but these surveys could not give us distances to the gas, only position on the sky and radial velocity.

The star surveys give us a better idea of distances, and indeed we appear to live in a barred spiral galaxy. Here is an artists conception of about what it looks like, though I am under the impression that the arms do not wind around quite so many times.
http://antwrp.gsfc.nasa.gov/apod/ap050825.html

Seen edge on it looks like this far-far-far infrared picture:
http://antwrp.gsfc.nasa.gov/apod/ap950908.html
That is real data taken from earth orbit, so you can see why it is hard for us to see if there is a bar. We surmise the bar from the velocity distributions of gas and stars towards the center.

Answer 5

Because there are only several shapes a galaxy can be. Looking through telescopes through the cross-section of our galaxy they determined what kind ours is.

Answer 6

What matters is not what we look like on the outside... but rather what is inside that counts.

(Sorry, but I had to throw it in)