On February 15, the New England-born California transplant John Adams turns a buoyant, boyish 80, but the London Symphony is starting the celebrations early. On the hourlong commuters’ special “Half Six Fix” on January 6, Sir Simon Rattle presents, with commentary, the 40-minute Harmonielehre, which he has characterized as the composer’s counterpart to Stravinsky’s Firebird. Harmonielehre also rings down Sir Simon’s full-length program for January 7 and 10, following the short symphony Frenzy and an excerpt from the Passover sequence in the opera The Gospel of the Other Mary. On January 13, Adams takes the podium himself to lead a playlist of his greatest hits, including Short Ride in a Fast Machine, Shaker Loops (the minimalist “Amazing Grace”), and the way-cool The Chairman Dances (from Nixon in China). The Icelandic superstar Víkingur Ólafsson joins the magic-carpet ride for the May-December lovefest After the Fall, a piano concerto written just for him. —Matthew Gurewitsch