In 1975, Nicholas Nixon lined up the Brown sisters—Mimi (age fifteen), Laurie (twenty-one), Heather (twenty-three), and Bebe (twenty-five), who is Nixon’s wife—and photographed them with an 8×10 view camera. He repeated the process every year for four decades, with the sisters always posed in the same order—youngest to oldest. The Brown Sisters: Forty Years (2014) collects all of the images, with their luxe black-and-white printing and unpretentiously pretty, strong women. Nixon’s earlier work was included in the landmark 1975 “New Topographics” group exhibition, and his “Brown Sisters” series has some affinity with that flat-affect style. But while many artists included in that show continued to document banal postindustrial landscapes, Nixon turned to investigate more affecting territory: time’s steady progression and the persistence of sisterly love. It is difficult, of course, to watch the Browns age without feeling solemn or trying to interpret their expressions from year to year—a smile turns into pursed lips, and then changes again into a grin. Yet it is a heartening project, too: Time passes, but the bond between the sisters remains intact.