With the aftermath of marathon bombings still hanging over Boston, Northeastern University began the city’s commencement season Friday to recognize its students’ achievements and the work of region’s first responders.

More than 20,000 students, family members, friends, faculty, and staff gathered in TD Garden Friday morning to cheer and celebrate the graduating class, but the joyous day was not without solemn reflection on recent events.

“While we have much to celebrate we are joined in the shadow of tragedy. Northeastern President Joseph E. Aoun said in his opening remarks. “We are feeling a conflicting mix of emotions: joy and pain, triumph and loss. Fortunately we also draw strength from one another.”

Aoun recognized the first responders, law enforcement officials, and ordinary citizens who helped at the finish line after the bombings, including Northeastern students in the Bouve College of Health Sciences originally there to offer first aid and routine assistance to marathon runners.