Hundreds of years ago explorers sailed across oceans and traversed uncharted continents to map Earth, and in the past half a century space probes have photographed most of our solar system. Yet as well as we have come to know our astronomical backyard, our image of the larger neighborhood—our Milky Way galaxy—is blurry. The reason is obvious: we cannot get outside it to take a peek. Imagine sending a spacecraft on a multimillion-year journey to go beyond our galaxy, look back and snap a picture: clearly impractical. We are left with many open questions about our cosmic home, such as how many spiral arms the galaxy has, whether the large structure closest to the sun counts as an arm and where in the galaxy our solar system lies.
Image: Credit: Ron Miller
