The eighth planet from the Sun, Neptune was the first planet located through mathematical predictions rather than through regular observations of the sky. When Uranus didn't travel exactly as astronomers expected it to, two mathematicians, working independently of each other, proposed the position and mass of another, as yet unknown planet that could account for Uranus' orbit. Although "the establishment" ignored the predictions, a young astronomer, Johann Gottfried Galle, decided to look for the predicted planet. Thus, Neptune was discovered in 1846. Seventeen days later, its largest moon Triton, was also discovered. Nearly 4.5 billion kilometers from the Sun, Neptune orbits the Sun once every 165 years.
© Copyright Rob Kantelberg
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