We have clearly entered the age of the sprawling cast. Popular series from “Lost” to “24” to “Studio 60” to “Prison Break” ask us to keep track of dozens of characters. And we oblige willingly. The same can be said of “Battlestar Galactica” (8 p.m., Sci Fi), a complex space opera featuring fleshed-out good guys and bad guys, humans and the robotic Cylons, who adopt human form. They also replicate, reproduce and resurrect themselves right before our eyes. Characters who believe themselves to be human turn out to be Cylon double agents. Cylons assigned to destroy humanity fall in love with individual humans. It can get confusing.

And rewarding. For the uninitiated, “Battlestar” concerns an ongoing war between humans and Cylons. Robots once created to take out the garbage and do other menial chores have evolved into a powerful race of brilliant Cylons. And boy are they mad.

After a sneak attack, humanity finds itself all but wiped out and driven into space exile. At the end of last season, president Laura Roslin (Mary McDonnell) was defeated by the slick Gaius Baltar (James Callis), a scientific genius. Roslin suspects he’s a Cylon dupe. And she’s right.

Under Baltar, a group of humans settle on an Earthlike planet named New Caprica. After a brief period of isolated refuge, they are discovered and attacked by the Cylons. Admiral Adama (Edward James Olmos) hides the Galactica and its small crew in deep space while the Cylons install a dictatorial regime on New Caprica. But, and it is a significant but, the Cylons do not annihilate the humans. A more moderate regime of deeply religious Cylons see it as their duty to bring both parties closer to God.

As the occupation becomes more brutal, Baltar becomes the despised figurehead of a collaborative government. But the humans held in the greatest contempt are those who join the police force of the occupying enemy.

“Galactica” taps into a theme central to American culture. We root for the rebel, no matter what the entertainment genre.

¢ Angelo Surmelis hosts “24 Hour Design” (7:30 p.m., HGTV), featuring one-room makeovers that take only a day. OK, they take only a day – with a budget of $2,000, a team of advice-dispensing experts and a crack carpenter.

Tonight’s other highlights

¢ On two episodes of “Meerkat Manor” (Animal Planet), a brawl ends in bloodshed (7 p.m.), Flowers is in no mood for her daughters’ antics (7:30 p.m.).

¢ A trip back to 1879 to meet Queen Victoria on the highlands on “Doctor Who” (7 p.m., Sci Fi).

¢ A wife’s testimony against her predator husband may be hiding darker family secrets on “Close to Home” (8 p.m., CBS).

¢ A random highway shooting may be part of a sick pattern on “Numb3rs” (9 p.m., CBS).

¢ A mysterious explosion at a posh brownstone takes a young victim on “Law & Order” (9 p.m., NBC).

¢ Scheduled on “20/20” (9 p.m., ABC): Has laziness become an American epidemic?