For Parisians at the end of the 19th century, to attend the opera, the ballet or the Moulin Rouge was to see but also to be seen. This spring the Mildred Lane Kemper Art Museum at Washington University in St. Louis will present “Spectacle and Leisure in Paris: Degas to Mucha.” Featuring a broad selection of prints, posters, photographs and film, the exhibition will explore how visual artists at once documented, promoted and participated in the distinctive entertainment cultures that defined the Belle Époque.