15 Eunomia facts for kids

Kids Encyclopedia Facts
15 Eunomia Astronomical symbol for 15 Eunomia
Discovered by Annibale de Gasparis
Discovery date July 29, 1851
Other names none
Category Main belt, (Eunomia family)
Reference date June 14, 2006 (JD 2453900.5)
Longest distance from the Sun 469.429 Gm (3.138 AU)
Shortest distance from the Sun 321.429 Gm (2.149 AU)
Longest distance from the center of its orbital path
("semi-major axis")
395.429 Gm (2.643 AU)
How long it takes to complete an orbit 1569.687 d (4.30 a)
Average speed 18.16 km/s
Mean anomaly 286.102°
Angle above the reference plane
Size and other qualities
Measurements 330×245×205
Mass 3.26±0.12×1019 kg
Average density 3.8±0.7 g/cm³
Surface gravity 0.08 m/s²
Escape velocity 0.16 km/s
Rotation period 0.2535 d (6.083 h)
How much light it reflects 0.209 (geometric)
Avg. surface temp. ~166 K
max: 260 K (-13 °C)
Spectral type S-type asteroid
Seeming brightness
("apparent magnitude")
7.9 to 11.24
True brightness
("absolute magnitude")

15 Eunomia is a very big asteroid in the closer part of the main asteroid belt. It is the biggest of the stony (S-type) asteroids, and somewhere between the 8th to 12th biggest Main Belt asteroid overall (unsure diameters make its ranking unsure). It is also the biggest member of the Eunomia family of asteroids.

Eunomia was found by Annibale de Gasparis on July 29, 1851 and named after Eunomia, one of the Horae (Hours), a personification of order and law in Greek mythology.


As the biggest S-type asteroid (with 3 Juno being a very close second), Eunomia has attracted a moderate amount of scientific attention. It has a bit over one percent of the mass of the entire main belt.

Eunomia appears to be a stretched but fairly round body, with what appear to be four sides of differing curvature and noticeably different average compositions. Its stretched shape led to the suggestion that Eunomia may be a binary object. However, this has been denied. It is a retrograde rotator with its pole pointing towards ecliptic coordinates (β, λ) = (-65°, 2°) with a 10° uncertainty. This gives an axial tilt of about 165°.

Like other true members of the family, its surface is made up of silicates and some nickel-iron, and is quite bright. Calcium-rich pyroxenes and olivine, along with nickel-iron metal have been detected on Eunomia's surface. Spectroscopic studies suggest that Eunomia has regions made up differently.

Eunomia has been seen occulting stars three times. It has a mean opposition magnitude of +8.5, about equal to the mean brightness of Titan and can reach +7.9 at a near perihelion opposition.

15 Eunomia Facts for Kids. Kiddle Encyclopedia.