CREATE TABLE table_name_26 (year__ceremony_ VARCHAR2, category VARCHAR2, actor_actress VARCHAR2)

What is the year when sigourney weaver was nominated for best actress?
SELECT year__ceremony_ FROM table_name_26 WHERE category = "best actress" AND actor_actress = "sigourney weaver"
SELECT "year__ceremony_" FROM "table_name_26" WHERE "actor_actress" = "sigourney weaver" AND "best actress" = "category"