“Life imitates art far more than art imitates life,” penned Oscar Wilde in an 1889 essay, “The Decay of Lying.” Yet “The Gettysburg Cyclorama: The Turning Point of the Civil War on Canvas” is one exception. The book’s writers, Chris Brenneman and Sue Boardman, who have worked as licensed guides at the Gettysburg National Military Park in Pennsylvania, acknowledge that there have been thousands of books written about the worst battle of the Civil War, with 51,118 casualties over three days. However, this book uniquely scrutinizes the battle from an artistic angle, specifically through Paul Philippoteaux’s immense, 19th-century cyclorama painting, “The Battle of Gettysburg.”…