The Boston Athletic Association (B.A.A.) will open registration for the 2012 B.A.A. Half Marathon, presented by Dana-Farber Cancer Institute and the Jimmy Fund, tomorrow, Wednesday, July 18, 2012, at 10:00 a.m. ET on the event’s website, BAA.org. The twelfth edition of New England’s premier half marathon is set for Sunday, October 7, 2012, and will be the final race in the inaugural B.A.A. Distance Medley. The B.A.A. Half Marathon begins in Boston’s scenic Franklin Park at 8:30 a.m. on the Sunday of Columbus Day weekend.