If we reside inside the Milky Way galaxy, how do we know what it looks like?
Here's the dilemma put in more words :
We think of our galaxy as being shaped like a big pinwheel. Yet we’ve never sent a camera outside of our galaxy to get an ‘outside view.’ How do we know our galaxy is shaped that way?
We can’t travel outside the galaxy to take pictures. A space probe moving at near light speed would take thousands of years to get far enough away to take a parting snapshot.
That was the question that was constantly bugging me as I read about the Big Bang.
After a quick google search, I got my answer, from various sources.
1) The distances to stars can be measured using several techniques, and since we know the direction to the stars , we can plot their positions on a 3D map (or 2D with some projection). With enough of the stars plotted, you can get a pretty accurate picture of the shape and size of the galaxy.
2) We have various techniques for measuring the distances to celestial objects. By taking the direction to an object and its distance from us, we can plot its location in space. Thus, even though we are inside of the Milky Way, we can figure out what it looks like by plotting the locations of the objects that we can "see". (Here, seeing includes using much more of the electromagnetic spectrum than just visible light. Dust in the galaxy blocks much of the visible light from other parts of the galaxy, but it does not block other frequencies.)
Sources :
http://www.answerbag.com/q_view/658287
http://curious.astro.cornell.edu/question.php?number=622
This article has lots of pictures and the chronological explanation as to how we arrived at the depiction of the Milky Way.(below)
"The most incomprehensible thing about the universe is that it is comprehensible." - Albert Einstein(great denier of the Big Bang model, but humble enough to admit he was wrong later on)
