Neptune was predicted before it was seen
海王星先有預測后發現

Neptune is the only planet in our Solar System whose existence and location was mathematically predicted before the planet was actually observed. French astronomer Urbain Le Verrier and British astronomer John Couch Adams both performed calculations to locate a possible new planet. In 1846, Le Verrir told German astronomer Johann Galle where to point Galle's telescope based on Le Verrier's calculations, and in about half an hour Galle found Neptune within one degree of its actual position--a dramatic confirmation of Newton's Law of Universal Gravitation.
海王星是太陽系中唯一一顆先由精確的數學推導預測出來，再通過觀察確定的行星。法國天文學家勒威耶和英國天文學家亞當斯都對這顆新行星的位置做出了計算。1846年，勒威耶讓德國天文學家加勒根據自己的計算擺放望遠鏡，半小時后，加勒就在勒威耶所計算的方向的一度范圍內發現了海王星，完美驗證了牛頓的萬有引力定律。