TONIGHT'S MUST-SEE

"Chuck," 7 p.m., NBC. Last week, Chuck met Jill (Jordana Brewster), the beauty he loved and lost in college. His long funk ended; his old love sparked. Now they're planning a weekend together. Except that his secret spy duty beckons. That involves feigning a relationship with Sarah; Jill will be fuming.

TONIGHT'S MIGHT-SEE

"Direct From the Moon," 4 and 7 p.m., National Geographic Channel. This is Expedition Week, filled with the epic projects. Yesterday, we saw evidence of an internal ramp used to build the Great Pyramid. Tonight, we get high-definition footage of and from the moon, shot by Japan's orbiter.

OF NOTE

"Santa Baby" (2006), 7 p.m., and "Holiday in Handcuffs" (2007), 9 p.m., ABC Family. In two weeks, this channel returns to its pleasant "25 Days of Christmas." To get us in the mood, here's a sampling. The first film is slickly filmed and fairly entertaining, with Jenny McCarthy as Santa's yuppie daughter. The second, with Melissa Joan Hart forcing Mario Lopez to be her fake boyfriend, strains believability.

"Einstein," 7 p.m., History Channel. It took Albert Einstein 15 years to prove his theory of relativity, this documentary says. Here's a portrait of the stretch when other scientists shunned him.

"The Big Bang Theory," 7 p.m., CBS. Wolowitz thinks he's found the perfect girlfriend.

"How I Met Your Mother," 7:30 p.m., CBS. Jamie-Lynn Sigler of "The Sopranos" plays Robin's new party friend.

"Two and a Half Men," 8 p.m., CBS. Women always seem to stay at Charlie's place; now one insists he stay at her place.

"Heroes," 8 p.m., NBC. Nathan is startled to see that his father Arthur is alive. There's more, though: After striking against Hiro and Ando, Arthur now goes after his wife, his younger son Peter and his granddaughter Claire.