Is Friday night the new Saturday? For the networks, the trend is all too clear. The Big Three have largely abandoned Saturday nights to repeats and the occasional movie because not enough viewers were tuning into original fare. What was the last Saturday night hit? “Dr. Quinn, Medicine Woman”? That was cancelled back in 1998.

CBS had a moderate Friday-night hit on its hands with “Joan of Arcadia” (7 p.m., CBS), but the ratings for that supernatural drama have long since come back down to Earth, and its audience continues to dwindle. Perhaps there are just so many stories you can generate about a girl who talks to God’s many incarnations. Tonight: Joan defies her mother and breaks a curfew.

Recently, CBS has enjoyed some success with its midseason decision to move the new show “Numb3rs” (9 p.m., CBS) to Fridays. Neil Patrick Harris (“Doogie Howser”) guest stars tonight.

NBC hopes to attract viewers with old-fashioned sweeps crossover trickery. Look for Dr. Connor (Neal McDonough, “Medical Investigation”) to pursue a case to New York on “Third Watch” (8 p.m., NBC). Later, Connor and Detective Yokas (Molly Price, “Third Watch”) collaborate on “Medical Investigation” (9 p.m., NBC).

Sometimes the most revealing aspect of sweeps month is the list of shows that don’t air at all. That’s never a good sign. The missing-in-action status of ABC’s “Complete Savages” and “Less Than Perfect” speaks volumes about their future prospects.

• Shot on location in New York City’s Harlem, the three-part miniseries “Miracle’s Boys” (8 p.m., Noggin) follows three orphaned teens trying to keep their family together. Based on a young-adult novel of the same name by Jacqueline Woodson, “Miracle” will air tonight, Saturday and Sunday. Five directors — Spike Lee, LeVar Burton, Ernest Dickerson, Bill Duke and Neema Barnette — collaborated on the project.

Pooch Hall stars as Ty’ree, the oldest brother, who defers his dream of attending MIT to raise his younger brothers, including Charlie (Sean Nelson), recently released from juvenile hall, and Lafaette (Julito McCullum), the “quiet” youngest brother often caught in the crossfire between his squabbling siblings.

Tonight’s other highlights

• Could the deflated ratings of “Joan of Arcadia” be due to cable competition from “Highway to Heaven” (7 p.m., TV Land) repeats?
• On back-to-back episodes of “Bernie Mac” (Fox), extracurricular dramatics (7 p.m.), an emotional cotillion (7:30 p.m.).
• Chris Beetem (“As The World Turns”) joins the cast of “JAG” (8 p.m., CBS).
• Julia Roberts, Annabeth Gish, Lili Taylor and Vincent D’Onofrio star in the 1988 coming-of-age film “Mystic Pizza” (8 p.m., Pax).
• The Declaration of Independence vanishes from its display case on “Jane Doe” (8 p.m., Hallmark), starring Lea Thompson.
• Scheduled on “20/20” (9 p.m., ABC): myths and misconceptions about dieting, skincare and other self-help products and techniques.

Series notes

On back-to-back episodes of “8 Simple Rules” (ABC), CJ feels used (7 p.m.); game, set and match (7:30 p.m.) … Phlox is admired from afar on “Star Trek: Enterprise” (7 p.m., UPN) … Things get frosty with Ben on “What I Like About You” (7 p.m., WB).

On back-to-back episodes of “Reba” (WB), an unorthodox agent (7:30 p.m.), Cheyenne’s eyes wander (8 p.m.).

Peta Wilson (“La Femme Nikita”) guest stars on “Jonny Zero” (8 p.m., Fox) … A plug for “Wife Swap” on an hour-long helping of “Hope & Faith” (8 p.m., ABC) … Missy Elliott hosts “The Road to Stardom” (8 p.m., UPN) … Macho mirth on “Blue Collar TV” (8:30 p.m., WB).

Late night

Rachel Weisz and Roseanne appear on “Late Show with David Letterman” (10:35 p.m., CBS) … Jay Leno hosts Steve Irwin, Sandra Oh and Joss Stone on “The Tonight Show” (10:35 p.m., NBC) … Sylvester Stallone appears on “Jimmy Kimmel Live” (11:05 p.m., ABC).

Charlie Sheen, Molly Sims and Emo Phillips chat on “Late Night with Conan O’Brien” (11:35 p.m., NBC) … Craig Ferguson hosts Julian Fellowes on “The Late, Late Show” (11:37 p.m., CBS).