CREATE TABLE table_21853 ("Episode" FLOAT, "Original title" CLOB, "Directed by" CLOB, "Written by" CLOB, "Original airdate" CLOB, "Duration" CLOB, "Viewership" CLOB)

What was the first airdate with a viewership of 4.77 million?
SELECT "Original airdate" FROM table_21853 WHERE "Viewership" = '4.77 million'
SELECT "Original airdate" FROM "table_21853" WHERE "Viewership" = '4.77 million'