“Nature’s Most Amazing Events” (8 p.m., Discovery Channel): “Nature’s

“Nature’s Most Amazing Events” (8 p.m., Discovery Channel): “Nature’s Most Amazing Events” is a breath-taking six-part documentary series that examines dramatic seasonal changes. Part 1: “Arctic Summer.”

“The Tonight Show” (11:35 p.m., NBC): Jay Leno ends his highly successful run on “The Tonight Show” with what should be an emotional farewell. But don’t shed too many tears because he’ll be back with a new prime-time show in the fall.