Harmonia (minor planet designation: 40 Harmonia) is a large main-belt asteroid. It was discovered by German-French astronomer Hermann Goldschmidt on March 31, 1856,^[6] and named after Harmonia, the Greek goddess of harmony. The name was chosen to mark the end of the Crimean War.

The asteroid is orbiting the Sun with a period of 3.42 years and a relatively low eccentricity of 0.046. It has a cross-sectional size of 107.6 km. The spectrum of 40 Harmonia matches an S-type (silicate) in the Tholen classification system, and is similar to primitive achondrite meteorites.^[7] Photometric observations at the Organ Mesa Observatory in Las Cruces, New Mexico during 2008–09 were used to generate a light curve that showed four unequal minima and maxima per cycle. The curve shows a period of 8.909 ± 0.001 hours with a brightness variation of 0.28 ± 0.02 in magnitude. This result is compatible with previous studies.^[4]

Speckle interferometric observations carried out with the Nicholas U. Mayall Telescope at the Kitt Peak National Observatory during 1982–84 failed to discover a satellite companion.^[8] In 1988 a search for satellites or dust orbiting this asteroid was performed using the UH88 telescope at the Mauna Kea Observatories, but the effort came up empty.^[9]