FRIDAY20 Years of Listening to America (PBS, 9-10:30 p.m.): Bill Moyers did the listening all this time on his public TV shows, and here are some delicious samples: informed and sometimes searching conversations with a startling variety of people - from Ronald Reagan to Maya Angelou to Joseph Campbell. These are only excerpts, but at their best they make you feel you're revisiting a life of the mind. SUNDAY Columbus and the Age of Discovery (PBS, 8-10 p.m.): Airing around the world, this new series - part of the Columbus quincentenary, of course - taps many sources in its sweeping, detailed chronology. It takes pains to locate Columbus squarely in his own 15th-century European setting - a place ripe for big changes - and explains how his obsessive hunt for a new trade route led not only to those changes, but to a whole new world. Ah, but is the show politically correct? Can a European 'discover' a continent where people have been living for millenia? Such questions have embroiled the producers in controversy. Yet a big viewership is expected anyway, especially with the aid of a little repackaging: Originally produced as seven separate weekly episodes, the series will now air in the popular miniseries form - on four consecutive nights, two at a time on the first three nights. (See preview in the Oct. 4 Monitor.) Ray Charles: 50 Years in Music, uh-huh! (Fox, 9:30-11 p.m.): That timeless elan - that irresistible buoyancy and depth - is applauded by millions. Now a long list of top-rank pop artists will perform in celebration of the great jazz pianist-singer's career. Charles himself sings too. Please check local listings, especially on PBS.