With so few traditional sitcoms on the air this year, the new ones had better be good. Happily for viewers, Fox's "Back to You" and CBS's "Big Bang Theory" qualify as generally welcome newcomers.

"Big Bang Theory" (8:30 tonight, KDKA) taps into the nerds-are-hot trend with its lead characters, brilliant physicists Sheldon (Jim Parsons) and Leonard (Johnny Galecki).

And, yes, fans of TV history, their names are an intentional nod to the late Sheldon Leonard, a TV writer/producer ("The Andy Griffith Show," "I Spy").

Leonard is the less nerdy of the pair, smart guys with stunted social skills. Leonard, at least, makes an effort. He invites attractive new neighbor Penny (Kaley Cuoco) over for dinner, but Sheldon is a little too free with his responses.

When Penny announces she's a Sagittarius, adding, "That tells you more than you need to know," Sheldon agrees, saying, "It tells us you participate in the mass cultural delusion that the sun's apparent position relative to arbitrarily defined constellations at the time of your birth somehow affects your personality."

Galecki, fondly remembered for his role on "Roseanne," is really the straight man here. Parsons, a relative newcomer with roles in "Judging Amy" and the movie "Garden State," gets all the best lines, quirks and embarrassing statements.

"Oh, that's interesting," Sheldon says after Penny announces she's a semi-vegetarian. "Leonard can't process corn."

The guys have two additional nerdy friends, attempting-to-be-suave Howard Wolowitz (Simon Hedberg) and too-shy-to-speak Rajesh Koothrappali (Kunal Nayyar).

Written by Chuck Lorre ("Two and a Half Men") and Bill Prady ("Dharma & Greg"), the show also benefits from a toe-tapping, if brief, theme song by Barenaked Ladies.

Then again, I suppose it could erupt into controversy if anti-evolution zealots get their knickers in a knot: The song mentions that the big bang happened 14 billion years ago and zooms through Earth history since that event.