From our limited perspective—living on a planet that orbits one of several hundred billion stars inside the Milky Way—the detailed structure of our home galaxy is difficult to determine. It has long been recognized by astronomers as a typical spiral galaxy, one of countless flattened pinwheels of stars seen throughout the universe. By mapping the distances to more than 2,400 stars, scientists have now created, with unprecedented precision, a three-dimensional map that shows the Milky Way has a twisted shape. [excerpt