Last stop before leaving the solar system

Official telescopic confirmation of Neptune's presence in our solar system came on September 23, 1846, and it was a big deal partly because Neptune is the only planet in our solar system not visible with the naked eye. Credit for this discovery inspired a dust-up in the international astronomy community, as scientists from both Britain and France claimed they had been the first to predict the existence and position of the eighth and most-distant planet in our solar system before it was seen through a telescope. Eventually peace was brokered, and credit is now shared between the two factions.
© NASA/JPL