"Nova: Wave That Shook The World," 8, "Krakatoa," 9, PBS. First, on "Wave," Nova takes an in-depth look at the Dec. 26, 2004, tsunami that devastated countries surrounding the Indian Ocean, leaving more than 250,000 people dead or missing. Scientists at the Pacific Tsunami Warning Center in Hawai'i tell of their frustrations in trying to determine what was happening and how to alert those in the path of the big waves. The British documentary "Krakatoa" powerfully recaptures the 1883 volcanic explosion and the Indonesian tsunami that followed.

Of Note

"American Idol," 7, Fox. After last week's chaos with the wrong phone numbers and a do-over the next night, "Idol" may return to normality. Ten contestants remain.

"Invasion Iowa" debut, 7, 9, Spike TV. Simultaneously fascinating and repulsive, this four-night reality series has William Shatner and others pulling an elaborate practical joke, convincing the people of Riverside, Iowa, that a science-fiction movie is being filmed there.

"The Office," 8:30, NBC. After the boss misbehaves, an expert gives a diversity workshop. When the expert leaves, the boss has a hilarious workshop of his own.

"Nashville Star," 10, USA Network. This show is at its best when contestants do songs they wrote themselves. Tonight, one finalist will be cut and the other six will perform.