Where is the Rest of the Universe?

This question is critical to astronomers, as they are unable to account for nearly 90 percent of the universe's mass. Two of the prominent scientists devoted to research in the area of this unseen, or "dark", matter are Vera Rubin of the Carnegie Institution in Washington, DC, a pioneer in the search for the mysterious missing mass, and Tony Tyson of Bell Laboratories, who travels to Chile and Hawaii to observe "gravitational arcs", which are the visible "fingerprints" of dark matter. Also featured is John Dobson, a self-proclaimed "sidewalk astronomer" who teaches classes in telescope making and travels to national parks around the country to host "star parties", where he invites the public to gaze at the heavens and ask him questions about the cosmos.