<Table> <Tr> <Th colspan="2"> Season </Th> <Th> Book </Th> <Th colspan="2"> Episodes </Th> <Th colspan="2"> Originally aired </Th> </Tr> <Tr> <Th> First aired </Th> <Th> Last aired </Th> </Tr> <Tr> <Td> </Td> <Td colspan="1"> </Td> <Td> Book One : Water </Td> <Td colspan="2"> 20 </Td> <Td colspan="1"> February 21 , 2005 ( 2005 - 02 - 21 ) </Td> <Td> December 2 , 2005 ( 2005 - 12 - 02 ) </Td> </Tr> <Tr> <Td> </Td> <Td colspan="1"> </Td> <Td> Book Two : Earth </Td> <Td colspan="2"> 20 </Td> <Td colspan="1"> March 17 , 2006 ( 2006 - 03 - 17 ) </Td> <Td> December 1 , 2006 ( 2006 - 12 - 01 ) </Td> </Tr> <Tr> <Td> </Td> <Td colspan="1"> </Td> <Td> Book Three : Fire </Td> <Td colspan="2"> 21 </Td> <Td colspan="1"> September 21 , 2007 ( 2007 - 09 - 21 ) </Td> <Td> July 19 , 2008 ( 2008 - 07 - 19 ) </Td> </Tr> </Table>
when did avatar the last airbender first air
February 21 , 2005