Chances are you only think you’ve heard Handel’s Messiah in its entirety. Most modern groups perform various parts of it, a trend that started right after its first performance in 1742, when Handel started fiddling with it, making a seemingly endless number of changes. Mercury Baroque, under the direction of Antoine Plante, is performing the whole piece in Complete Messiah. Enjoy the baroque masterpiece as it was first heard — in its entirety and on period instruments — at 8 p.m. today. Wortham Theater, 501 Texas. For information, call 713-533-0080 or visit www.mercurybaroque.org. $22 to $59.

Sat., Dec. 10, 2011