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

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'