Trouble in the Heavens

      

      Astronomers determined that Uranus's orbit around 
      the Sun took 84 years. But after tracking Uranus for several years, astronomers 
      realized something was amiss with their calculations.
      
 According 
        to Newton's Law of Gravity, Uranus should move about the Sun in a certain 
        orbit, whose ellipticity would be determined by its mass, distance from 
        the Sun, and small gravitational effects of Jupiter and Saturn. In other 
        words, Uranus should behave in a predictable manner, if it had any respect 
        for science. It didn't, and scientists were duly perplexed. Was Newton's 
        Law wrong? 
      
 In 1824, the German mathematician Friedrich Bessel suggested that the 
        errors in Uranus's motion would be explained by the discovery of another 
        planet farther out. Of course, some argued that Newton's Law was not universal, 
        as previously advertised, but was only valid out to Saturn--beyond that 
        it required modification.
      
 This was deemed a rather compromising solution to an elegant law of 
        physics, and by the end of the 1830s astronomers generally acknowledged 
        that there was an undiscovered planet whose gravitational attraction caused 
        Uranus's troubled motion.
      
 
      

        Next: A Discovery and a Scandal
        
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