Nova (PBS, 8-9 p.m.): You can get a feel for some 2 billion years of physical history in "Rafting Down the Grand Canyon." By tracing 19th-century explorer John Wesley Powell's first trip down the canyon, the adventure documentary describes the effects not only of geology, but also of 30 years of human intervention on this natural wonder. Narrated by Gregory Peck and Linda Hunt.

Frontline (PBS, 9-10 p.m.): The numbers alone are enough to get your attention: $400 million for instance, which is roughly what the current presidential campaigns will end up costing - $9 million of it raised in one "President's Dinner" last April. Yes, nearly everyone knows money and politics are intertwined, but the true relationship between big givers and big politicians can be hard to grasp without the kind of inside look provided by "The Best Campaign Money Can Buy," an investigative report in the careful but unblinking style typical of this distinguished documentary program. It takes a relatively long view, including looks at Hubert Humphrey's pre-vice-presidential days in 1948. Today's largest contributors are identified and their connections explored. Clinton-campaign fundraiser Thomas Boggs sums it up this way: "There are three very important things in politics - money, money, and money."

Please check local listings for all programs, especially those on PBS.

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