As the architect of the Chicago Underground collective during the 90s--heading bands ranging in size from a duo to the five-piece Chicago Underground Orchestra--cornetist Rob Mazurek accomplished the tricky task of attracting both radicals and conservatives. Often working with like-minded guitarist Jeff Parker, he kneads an almost quaint lyricism into modernist, even experimental investigations of harmony and form; he also does a spectacular job of blending natural and electronic sounds on records like Chicago Underground Quartet (Thrill Jockey), the last album he made before leaving Chicago for Brazil in 2001. For his first show here since February of last year, he's put together a band conceived specifically for Millennium Park's "Made in Chicago" jazz series. The 14-piece Exploding Star Orchestra has more than enough power to light up the night sky, pooling the talents of (among others) Mazurek and Parker, reedists Ken Vandermark and David Boykin, flutist Nicole Mitchell, bassist Jason Ajemian, terrific young trumpeters Corey Wilkes and Josh Berman, and pianist and synth whiz Jim Baker. The lineup is an impressive cross section of Chicago's improv jazz community, and it's also noteworthy for including black and white musicians from both sides of town, bridging a north-south divide that--though it's begun to break down in recent years--has existed in Chicago's progressive music scene since the 60s. The Chicago Vocational Career Academy Marching Cavaliers open. Thu 8/5, 5:30 PM, Pritzker Pavilion, Millennium Park, 100 N. Michigan, 312-742-1168. Free. All ages.