878 Mildred is a

minor planet According to the International Astronomical Union (IAU), a minor planet is an astronomical object in direct orbit around the Sun that is exclusively classified as neither a planet nor a comet. Before 2006, the IAU officially used the term ''minor ...

in the

main belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...

orbiting the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. It is the lowest numbered, and thus the namesake, of the Mildred family of asteroids, a subgroup of the

Nysa family The Nysa family (adj. ''Nysian''; FIN: 405) is part of the Nysa–Polana complex, the largest cluster of asteroid families in the asteroid belt. It is located in the inner region of the asteroid belt, orbiting the Sun between 2.41 and 2.5 A ...

. The Mildred subgroup, and by extension 878 Mildred itself, is thought to have been formed by a recent fragmentation event from a larger asteroid.

Discovery

878 Mildred was originally discovered in 1916 using the 1.5 m Hale Telescope at the

Mount Wilson Observatory The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles. The observat ...

, but was subsequently lost until it was again observed on single nights in 1985 and 1991 (a

lost asteroid A minor planet is "lost" when today's observers cannot find it, because its location is too uncertain to target observations. This happens if the orbital elements of a minor planet are not known accurately enough, typically because the observat ...

). Initially only two observations of the asteroid were taken on 1916-09-06 which does not allow for an accurate orbital determination, however interest in the object prompted further investigation and more measurements were taken in late September and October. The asteroid was re-discovered in 1991 by Gareth V. Williams. It is named after

Mildred Shapley Matthews Mildred Shapley Matthews (February 15, 1915 – February 11, 2016) was a book editor and writer known for astronomy books. She was the daughter of astronomers Harlow Shapley and Martha Betz Shapley; her father named the asteroid 878 Mildred for he ...

Physical properties

By comparing the asteroid's perceived brightness and the then computed distance from the Sun they arrived at an

absolute visual magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it ...

of 14.3, which if one assumes Mars-like albedo gives an approximate diameter of 3 to 5 kilometers.

References

External links

Minor Planet Center Database entry on (878) Mildred
* * 000878 Discoveries by Seth Nicholson Discoveries by Harlow Shapley Named minor planets 19160906 {{S-beltasteroid-stub