134 Sophrosyne is a large main-belt asteroid that was discovered by German astronomer Robert Luther on 27 September 1873. It was named after the concept of sophrosyne, Plato's term for 'moderation'. Classified as a C-type asteroid, 134 Sophrosyne has an exceedingly dark surface and most probably a primitive carbonaceous composition.
This object is orbiting the Sun at a distance of with an eccentricity of 0.12 and an orbital period of 4.10 years. The orbital plane is inclined at an angle of 11.6ð to the plane of the ecliptic.
An occultation of a star by 134 Sophrosyne was observed 24 November 1980, in the United States. Timing information from this event allowed a diameter estimate of 110 km to be derived. This is similar to diameter estimates of 108 and 112 km, achieved by other techniques. Photometric observations of the asteroid in 2015 produced a lightcurve indicating a rotation period of with a variation amplitude of in magnitude. This provided a good match to the only previous determination in 1989.