A woman’s depression threatens to ruin her wedding reception. A planet is on a collision course with Earth. Writer-director Lars von Trier uses the second of these two apparently unconnected plotlines to illuminate the first, sketching a vivid, insightful, at times wrenching portrait of the titular ailment along the way. He is abetted by the actors’ heartfelt performances. The whole movie is beautiful to look at, especially the stunning opening montage of painterly super-slow motion images.