Though “Dance: Movement, Rhythm, Spectacle” occupies just one large room (arranged to feel like three) at the Philadelphia Museum of Art, it seems to open windows in many directions. Its exhibits range from the 1890s to the 1980s, vividly demonstrating how radically that century brought change to social dance, dance theater and ideas of dance in art. Diversely diverse, the show, which opened this month, offers a panoply of artistic media (photographs, paintings, watercolors, prints, woodcuts, etchings, graphite drawings, lithographs and film), dancers of various races and a huge assortment of dance costumes.