<Tr> <Td_colspan="2"> List of The Big Bang Theory episodes </Td> </Tr> <P> The third season of the American sitcom The Big Bang Theory was originally aired on CBS from September 21, 2009 to May 24, 2010 with 23 episodes . It received higher ratings than the previous two seasons with over 15 million viewers . Season three started three months after the end of season two when the guys left for the North Pole . </P> <P> The third season saw the first appearances of future main cast members Melissa Rauch as Bernadette Rostenkowski in "The Creepy Candy Coating Corollary" and Mayim Bialik as Dr. Amy Farrah Fowler in the season finale "The Lunar Excitation". Christine Baranski submitted the episode "The Maternal Congruence" for consideration due to her nomination for the Primetime Emmy Award for Outstanding Guest Actress in a Comedy Series at the 62nd Primetime Emmy Awards . Jim Parsons won the Primetime Emmy Award for Outstanding Lead Actor in a Comedy Series at the 62nd Primetime Emmy Awards for the episode "The Pants Alternative". </P> <P> Penny throws herself at Leonard after he returns from three months at the North Pole, and they begin a relationship that lasts most of the season . Penny and Sheldon start a quirky friendship (though she can still annoy him). Wil Wheaton begins appearing as Sheldon's arch - enemy . Howard begins to date Bernadette Rostenkowski . At the end of the season, Sheldon meets Amy Farrah Fowler . </P>

When do amy and bernadette come into the big bang theory