Season 1 PBS , 1989 Season 2 PBS , 1990 Season 3 PBS , 1991 Season 4 PBS , 1992 Season 5 PBS , 1993 Season 6 PBS , 1994 Season 7 PBS , 1995 Season 8 PBS , 1996 Season 9 PBS , 1997 - 2006 Season 10 PBS , 1998 Season 11 PBS , 1999 Season 12 PBS , 2000 Season 13 PBS , 2001 Season 14 PBS , 2002 Season 15 PBS , 2003 - 2004 Season 16 PBS , 2004 Season 17 PBS , 2005 Season 18 PBS , 2006 Season 19 PBS , 2007 Season 20 PBS , 2008 Season 21 PBS , 2009