Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_17641206_4 ( original_airdate VARCHAR, viewership VARCHAR )

### Question ###
What was the first airdate with a viewership of 4.77 million?

### Accurate SQL ###

SELECT original_airdate FROM table_17641206_4 WHERE viewership = "4.77 million"