Triton, the son of Poseidon (the Greek equivalent of the Roman God Neptune) in mythology, is the largest of the thirteen moons of Neptune that have been discovered. It was discovered in 1846, a mere seventeen days after its planet was found, by the English astronomer William Lassell. It is one of the largest moons in the entire Solar System—it is around 1,700 miles, or about 2,700 kilometers, in diameter. It is approximately 2.8 billion miles away from the sun, and its average temperature is only a meager 38 Kelvin, or minus 235 degrees Celsius! This temperature is low enough to freeze nitrogen; hence, most of Triton is covered in nitrogen ice. However, what really sets Triton apart from its celestial counterparts is the fact that this satellite is geologically active—although just a few degrees away from the absolute zero, where all motion of atoms abruptly stops, the moon Triton is dramatic and alive with movement. In addition, this body rotates in a retrograde orbit (i.e. it rotates in a direction opposite to that of Neptune), and possesses a synchronous orbit with Neptune—which means that one side of the moon faces one side of the host planet at all times.