Dysnomia is the only known moon of the dwarf planet Eris. It was found on September 10, 2005 by Michael E. Brown and his team at the W. M. Keck Observatory. It is probably about 600 km in diameter (across), although it may be up to 800 km in diameter. The moon was named "Dysnomia" (from the Ancient Greek word that means "lawlessness") after the daughter of the Greek goddess Eris.