Neptune was predicted before it was seen
海王星先有预测后发现

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.
海王星是太阳系中唯一一颗先由精确的数学推导预测出来，再通过观察确定的行星。法国天文学家勒威耶和英国天文学家亚当斯都对这颗新行星的位置做出了计算。1846年，勒威耶让德国天文学家加勒根据自己的计算摆放望远镜，半小时后，加勒就在勒威耶所计算的方向的一度范围内发现了海王星，完美验证了牛顿的万有引力定律。