The dog days are upon us, bringing triple digits, brownouts, repeats and talent shows. OK, “Big Brother: All-Stars” (8 p.m., CBS) is not a repeat, but with its recycled cast, it sure seems like one. How many times can you hear the antics of somebody named Nakomis and not feel like you’re in a cruel time warp?

The results shows of both “America’s Got Talent” (9 p.m., NBC) and “So You Think You Can Dance” (9 p.m., Fox) go head-to-head, offering viewers the choice between imported British beauty Cat Deeley and the homegrown avuncular charms of the indefatigable Regis Philbin.

Both shows have been among the most-watched shows of the summer, with “Talent” the second most-popular show of the week ending July 23. But who’s really counting in the middle of the summer, when “CSI: Miami,” with the wooden David Caruso, is the No. 1 show of the week?

¢ Cinemax continues its weekly showcase for Oscar-nominated 2005 documentary shorts. Directed by Steven Okazaki, “The Mushroom Club” (6 p.m., Cinemax) interviews survivors of the atomic blast that devastated Hiroshima on Aug. 6, 1945. An elderly woman was a 25-year-old newlywed when the bomb fell. Although nearly every building in Hiroshima has been rebuilt, she still scours the streets and riverbanks for grim mementoes of the occasion. She has collected buttons torn from the clothes of blast victims, bits of melted glass and pieces of ceramics fused together by the heat.

“Mushroom” also looks at changing attitudes toward the war, defeat and occupation and Japan’s post-war policy of pacifism. Japan’s policy of renouncing war is so ingrained that people think nothing of a cigarette brand named Peace. But a small-but-growing minority calls for the return of Japan’s military and its days of “glory.”

¢ “Unstoppable Train” (7 p.m., National Geographic) recalls a railroad nightmare that struck near San Bernardino, Calif., when brakes failed, sending an overloaded freight train on a collision course with a small town and a petroleum pipeline.

¢ Susan Hayward faces the gas chamber in the 1958 potboiler “I Want to Live!” (9 p.m., TCM), directed by Robert Wise. It’s one of 14 movies starring Hayward airing today on TCM from 5 a.m. through early Friday morning

Tonight’s other highlights

¢ Bad memories of a camp for troubled boys on “My Name is Earl” (7 p.m., NBC).

¢ Chris obsesses about style and money on “Everybody Hates Chris” (7 p.m., UPN).

¢ Michael makes a field trip to New York City on “The Office” (7:30 p.m. NBC).

¢ A housewife takes a fatal tumble down a flight of stairs on “CSI” (8 p.m., CBS).

¢ A student considered long dead may live yet on “Without a Trace” (9 p.m., CBS).

¢ Nina feels guilty on “Windfall” (9 p.m., NBC).

¢ Scheduled on “Primetime” (9 p.m., ABC): an update report on a juvenile court.

¢ Azazeal targets Ella on “Hex” (9 p.m., BBC America).