Source: https://science.nasa.gov/neptune/facts
Title: neptune
Selected source excerpts (not the complete document).

Galileo recorded Neptune as a fixed star during observations with his small telescope in 1612 and 1613. More than 200 years later, the ice giant became the first planet located through mathematical predictions rather than through regular observations of the sky. Because Uranus didn't travel exactly as astronomers expected it to, French mathematician Urbain Joseph Le Verrier proposed the position and mass of a then-unknown planet that could cause the observed changes to Uranus' orbit. Le Verrier sent his predictions to Johann Gottfried Galle at the Berlin Observatory, who found Neptune on his first night of searching in 1846. Seventeen days later, Neptune's largest moon Triton was discovered as well.

Neptune’s axis of rotation is tilted 28 degrees with respect to the plane of its orbit around the Sun, which is similar to the axial tilts of Mars and Earth. This means that Neptune experiences seasons just like we do on Earth; however, since its year is so long, each of the four seasons lasts for over 40 years.
