Neptune is the eighth and farthest planet from the sun. It was discovered in 1846 by German astronomer Johann Gotfried Galle based on orbital calculations by French mathematician Urbain Le Verrier. 

In 1781, William Herschel discovered Neptune's twin Uranus. But astronomers noticed that that planet's orbit deviated from the strict Newtonian model. John Couch Adams and Le Verrier independently predicted another planet beyond Uranus to account for these irregular motions. Though Adams never published his predictions, Le Verrier did. Galle and his student Heinrich L. d'Arrest used those predictions to help him search the sky, and he found the eighth planet within one degree of where Le Verrier's numbers predicted it to be.
