“The orchestra’s 2009-10 season… will culminate in a four-week circus festival involving actual circus performers such as the Cirque de la Symphonie.” The repertoire for “BSO Under the Big Top” next March includes Corigliano’s Third Symphony (subtitled “Circus Maximus”), “an evening of concert operas by Barber and Gershwin and Stravinsky’s ballet Pulcinella.”