On Friday ESPN will launch a yearlong series called SportsCentury. In half-hour shows on Fridays at 10:30 p.m., the network will reveal—and profile—its choices for the 50 greatest athletes of the 1900s (the first program is devoted to No. 50, Chris Evert). More enthralling will be six bimonthly two-hour SportsCenter of the Decade shows (the first, covering 1900 to '49, is also scheduled for Friday night, at 8:30), in which the anchors appear in period dress and coifs. Watching the entire series will earn a viewer a degree from Bristol University.