Uranus and 4 Vesta had most probably been seen but could not be recognized as planets because they appear so faint even at maximum brightness ; Uranus ' magnitude varies from + 5.3supm / sup to + 5.9supm / sup , and Vesta 's from + 5.2supm / sup to + 8.5supm / sup ( so that it is only visible near its opposition dates ) .