On March 13, 1781, the world was shocked to learn of a sixth planet. For thousands of years, stargazers had noted the movements of five "wanderers" in the sky: Mercury, Venus, Mars, Jupiter, and Saturn. The five planets, plus Earth and the sun, totaled seven, the number of perfection. How had a planet been missed? Telescopes had been in use for 180 years. Not only that, the new planet was visible to the naked eye. British astronomer William Herschel found it by accident. He wanted to call it "Georgian Sidus" after King George III. Others had a different idea, and we nearly had a planet "Herschel." In the end, though, tradition held: The planet was named for the Roman god of the heavens, Uranus.
Source: 'Strange Universe,' by Bob Berman (Henry Holt, 2003).