Last winter, Professor Henry Louis Gates Jr. hosted the four-part series “African American Lives,” using oral history, family anecdotes, legal documents, genealogy and DNA analysis to trace the roots of several prominent African-Americans, including Whoopi Goldberg, Oprah Winfrey and Quincy Jones.

Gates returns with a one-hour special concentrating on the family and genealogy of only one star, or rather the one-and-only star. “Oprah’s Roots: An African American Lives Special” (7 p.m., PBS) revisits Winfrey’s difficult childhood and stories of her father’s tough love and inspiration. Then, just as it did last year, it peels away the layers of its subject’s past one generation at a time.

During this hour, Winfrey discovers things about her grandfather she never knew and learns that even more distant ancestors shared her passion for education. As a man in his 70s, her paternal grandfather helped with a 1966 rural Mississippi voter-registration drive. As Gates explains, that was a time when such actions by a black man could still provoke violent and even fatal retribution from white supremacists. A cross was burned on her grandfather’s property.

Gates does an entertaining job of exploring personal lives and presenting them in historical context. He also reveals a wealth of statistical and archival material available, including land deeds and census records that make it possible to trace family history back generations.

You don’t have to be a fan of the daytime talk-show host to find this interesting. And as Gates makes clear, this information is available to everyone of every background who is willing to do the work.

¢ Robert Irvine hosts “Dinner Impossible” (9 p.m., Food Network). Irvine’s background includes a stint as chef to Britain’s royal family as well as working in the White House kitchen under four American presidents.

“Impossible” will ask Irvine to create memorable meals under incredible pressure. In the first of two “Impossible” tasks airing tonight, he has 10 hours to create 1,000 appetizers and prepare a sit-down wedding dinner for 200. In the second installment (9:30 p.m.), he has four hours to scrounge food, spices, silverware and equipment from tailgate revelers at a football game and cook a lunch for 40 NFL executives.

¢ On tonight’s repeat of “The Sopranos” (8 p.m., A&E), Tony deals with some grim business while on a college-tour trip with Meadow. I try to resist hyperbole and superlatives, but this is the strongest and most powerful episode from the best season of the greatest TV drama.

Tonight’s other highlights

¢ New Yorkers audition on “American Idol” (7 p.m., Fox).

¢ An empty nest looms on the sixth-season premiere of “George Lopez” (7 p.m., ABC).

¢ “Is It Real?” (8 p.m., National Geographic) explores evidence of life on Mars.

¢ Murder intrudes on a meeting of movers and shakers on “CSI: NY” (9 p.m., CBS).

¢ A spirit proves uncooperative on “Medium” (9 p.m., NBC).

¢ Scheduled on “Primetime” (9 p.m., ABC): medical mysteries.