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It's a peculiar comment on our place in the universe that we know more about the structure of galaxies that are millions of lightyears away than we do about our own galaxy. This is primarily because much of the Milky Way is obscured by dust and stars and giant molecular clouds within the galaxy itself. Our situation can be likened to describing the outlines of a forest from the inside: All we can see are the trees immediately around us. Fortunately for astronomers, certain wavelengths of light are able to pass through the obscuring dust to varying degrees. With some clever subtracting and guesswork astronomers are able to "cut down the nearest trees" so as to see distant reaches of the galaxy that are otherwise obscured. Freudenreich provides an update on what astronomers have learned about the grand-scale shape of the Milky Way using these techniques.
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