Charon, the first of Pluto's satellites to be discovered, was first seen at the United States Naval Observatory by James W. Christy.

Charon, formal designation (134340) Pluto I, is the largest of the five known natural satellites of the dwarf planet Pluto. It has a mean radius of 606 km (377 mi). Charon is the sixth-largest known trans-Neptunian object after Pluto, Eris, Haumea, Makemake, and Gonggong. It was discovered in 1978 at the United States Naval Observatory in Washington, D.C., using photographic plates taken at the United States Naval Observatory Flagstaff Station (NOFS).

The United States Naval Observatory (USNO) is a scientific and military facility that produces geopositioning, navigation and timekeeping data for the United States Navy and the United States Department of Defense. Established in 1830 as the Depot of Charts and Instruments, it is one of the oldest scientific agencies in the United States, and remains the country's leading facility for astronomical and timing data.

James Walter "Jim" Christy is an American astronomer known for discovering Charon, the largest moon of the dwarf planet Pluto.