How many different numbers of people in the US who'd seen the episode with a season number 8 are there?
CREATE TABLE "table1_19925114_1" (
  "no_in_series" real,
  "no_in_season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_millions" text
);
SELECT COUNT("u_s_viewers_millions") FROM "table1_19925114_1" WHERE "no_in_season"=8;