Remember when late-night TV legend Johnny Carson took extended breaks from The Tonight Show, leaving a revolving cast of guest-hosts (Bob Newhart, David Letterman, Joan Rivers) to crack jokes in his stead? The 2012-2013 season at the Phoenix Symphony will be kind of like that. Officially, outgoing music director Michael Christie is still in charge, but the 38-year-old maestro will be frequently MIA this year as he gets new tuxedo tails measured at the Minnesota Opera. In his place, a talented mob of guest conductors will lead Arizona’s only full-time professional symphony, beginning with Harvard graduate and New York Times profilee Sarah Hicks, who opens the season on Thursday, September 20 by guiding acclaimed violinist Elena Urioste through Beethoven’s “Violin Concerto in D Major.” Also coming to the Valley are such orchestral up-and-comers as Tito Muñoz and Ignat Solzhenitsyn, performing the likes of Ravel, Stravinsky, Brahms, Rachmaninoff and Prokofiev. Christie will conclude his eight-year tenure at the symphony on Saturday, May 11, 2013 with Mozart’s “Symphony No. 8.” No word on who his Jay Leno will be. For more information and to purchase tickets, visit phoenixsymphony.org.