TONIGHT'S MUST-SEE

"Nova: Car of the Future," 8 p.m., PBS. On an Earth Day stuffed with eco-programs, this hour stands out. Tom and Ray Magliozzi of radio's "Car Talk" lead an intelligent and far-ranging look at automobiles. At the Detroit car show, they groan about 500-horsepower engines but find promise in the Prius and the Chevrolet Volt prototype. At an alternative show in Boston, they try a micro-car that gets 100 miles a gallon but has no reverse. Elsewhere, ideas range from hydrogen-powered buses in Iceland to handcrafted electric cars from Tesla Motors in California. This smart, skeptical hour traces the potential and limits of ethanol, lithium-ion batteries and more.

OF NOTE

Kids' shows, 6 a.m., Disney Channel; PBS. Both channels have Earth Day themes. That includes new episodes of "Handy Manny" (6 a.m. Disney) and "Super Why" (8 a.m. PBS). Kids will find those two moderately entertaining; adults won't.

"Big Ideas for a Small Planet," 6 p.m., Sundance Channel (Oceanic Digital 646). This upbeat hour finds people in their 20s who are passionate about ecology. It ranges from eco-weddings to the plans of Guster and other rock bands.

"American Idol," 7 p.m., Fox. It's a night for Andrew Lloyd Webber's Broadway songs. That means anything from the over-the-top rock of "Jesus Christ Superstar" to the power ballads of "Evita" and "Phantom of the Opera."

"NCIS," 7 p.m., CBS. When an arms dealer is killed NCIS director Jenny Shepard (Lauren Holly) is a prime suspect.

"Work Out," 7 p.m., Bravo. Late in this hour, the gym's women (most of them heterosexual) become trainers on a lesbian cruise. There will be more next week, but for now many viewers will enjoy the bikini-shopping spree.

"The Riches," 7 p.m., FX. In a raw and pivotal hour, Dahlia crumbles after learning that Pete was (accidentally) killed.

"Saturday Night Live: Best of Chris Farley," 7:30 p.m., NBC; "John Oliver: Terrifying Times," 7 p.m., Comedy Central. These reruns offer two great talents. The late Farley did sketch comedy, Oliver does standup, both are hilarious.

"Boston Legal," 9:02 p.m., ABC. Alan argues an appeal in the Supreme Court; meanwhile, Katie learns a secret about Jerry's too-beautiful girlfriend.

Also: There are many more Earth Day shows. PBS reruns a "Frontline" look at global warming at 9 p.m. There are marathons on Current and HGTV and more.