Neptune

© NASA/JP

Last stop before leaving the solar system

Official confirmation of Neptune's presence in our solar system came on September 23, 1846. 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 see the 8th and most distant planet in our solar system. Eventually, peace was brokered, and credit is now shared between the two factions. But those 19th-century astronomers were using solar system coordinates first recorded by Galileo in 1612. The Italian polymath correctly mapped Neptune's position more than 200 years earlier using a less powerful telescope. Galileo mistook Neptune for a star – but his coordinates prompted many stargazers who came along after him to look in the correct direction and identify Neptune.