Colm Keegan made his mark as a principal singer in the well-known Celtic Thunder, but before he embarked upon a performance career, he was a high school music teacher, with a master’s degree in music. For years, he’s though about a way to merge Irish history with music, and there never seemed like a good way to do it—until now. On Saturday, March 9, Keegan brings the first chapter of a new series called Irish History through Music to the Commodore John Barry Arts & Cultural Center.