What year did Galileo first discover Neptune?

Galileo is credited with observing Neptune for the first time in 1612, although he did not recognize it as a planet. Instead, he thought it was just another star in the night sky. This observation is significant because it marks one of the earliest recorded sightings of Neptune.

The other years listed do not correspond to any of Galileo's discoveries related to Neptune. The confusion often arises from the fact that Neptune was not officially recognized as a planet until its re-discovery in 1846 by Johann Galle and Heinrich d'Arrest, which is much later than Galileo's initial observation. Therefore, the year 1612 is pivotal in the history of astronomy as it represents the first documented sighting of a planet that would later be recognized as Neptune.