CREATE TABLE table_21979779_1 (original_air_date VARCHAR2, us_viewers__million_ VARCHAR2)

when was the premiere of the episode where the amount of North American spectators was 1.76 millions?
SELECT original_air_date FROM table_21979779_1 WHERE us_viewers__million_ = "1.76"
SELECT "original_air_date" FROM "table_21979779_1" WHERE "1.76" = "us_viewers__million_"