Welcome to On the Radar, where we preview upcoming events to mark your calendars for. You may have seen Iron Man 2, but you don’t know Stark about the Avengers until you’ve answered their call to arms. In honor of the Heroic Age and the launching of a half-dozen new Avengers titles, Marvel Comics has declared today, May 19, Avengers Day! This weekend, nationwide, comic shops will celebrate the first-ever event with limited edition prints and variant comics. But an Avenger’s job is never done — especially at Tampa’s Heroes’ Haven, which hosts an Avengers Day celebration, where Avengers of all ages assemble for a variety of comic, graphic novel and merchandise sales, costume contests (capes optional, clothing not), autograph and Q&A sessions with industry professionals including