On this day October 10 in 1846 – British astronomer, William Lassell discovered Neptune’s Moon Triton.

This discovery came only 17 days after the planet itself was discovered. After Herschel had learned of the discovery of Neptune – he contacted his mate Lassell and suggested he start the search for mons. Eight days later he discovered one.

William Lassell was a brewer by trade and had built and designed the ‘2 foot reflector’. This telescope was a metal speculum is 24 inches in diameter and of 20 feet focal length, and that the telescope is mounted equatorially. In 1848 he also discovered Saturns Moon Hyperion.

This telescope was the world’s first large reflector to have full motions in the equatorial plane, and to be possible for a single individual to use. In 1852, Lassell took the telescope to Malta. Then in the mid 1860s, he bought an estate at Maidenhead near London and set about building an observatory in the grounds. It was there, at Ray Lodge, that the telescope remained for the rest of his life. He died in 1880 and his daughter donated the telescope to the Royal Greenwich Observatory in 1883.

Triton is the 7th biggest moon in the solar system and is the only large moon in the solar system to have a retrograde orbit. It is also thought to be a Kuiper Belt Object captured by Neptune’s gravity.

The picture above was taken by Voyager 2 in its flyby in 1989.