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.