15 Eunomia

Discovery A
Discoverer	Annibale de Gasparis
Discovery date	July 29, 1851
Alternate designations	none B
Category	Main belt, Eunomia family
Orbital elements C D
Epoch October 22, 2004 (JD 2453300.5)
Eccentricity (e)	0.186
Semi-major axis (a)	395.872 Gm (2.646 AU)
Perihelion (q)	322.290 Gm (2.154 AU)
Aphelion (Q)	469.453 Gm (3.138 AU)
Orbital period (P)	1572.323 d (4.30 a)
Mean orbital speed	18.15 km/s
Inclination (i)	11.732°
Longitude of the ascending node (Ω))	293.399°
Argument of perihelion (ω)	97.577°
Mean anomaly (M)	148.829°
Physical characteristics
Dimensions	255.3 km
Mass	8.4 1018 kg
Density	0.96 g/cm³ 1
Surface gravity	0.0343 m/s²
Escape velocity	0.0935 km/s
Rotation period	0.2535 d (6.083 h) 2
Spectral class	S-type asteroid
Absolute magnitude	5.28
Albedo	0.209 3
Mean surface temperature	~166 K

15 Eunomia (ew-noh'-mee-a) is the 12th largest Main belt asteroid. It is also the largest member of the Eunomia family of asteroids. Like other true members of the family, it is composed of silicates and nickel-iron. It is light in colour.

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

Eunomia has rather variable lightcurve indicating an elongated object. This led to a suggestion that Eunomia may be a binary object. However, it was refuted later. [1]

Eunomia has been observed occulting stars three times.

Eunomia in fiction

One chapter of Arkady and Boris Strugatsky's novel Space Apprentice (1962) is staged on Eunomia. A scientific station on the asteroid is annihilating large fragments of the asteroid in its advanced experiments.

Appearance

Stationary, retrograde	Opposition	Minimum distance (AU)	Maximum brightness (mag)	Stationary, prograde	Conjunction to Sun
4 March 2005	30 April 2005	2.14777	9.8	18 June 2005	10 December 2005
10 June 2006	30 July 2006	1.47916	8.3	17 September 2006	16 April 2007
23 November 2007	10 January 2008	1.47650	8.2	26 February 2008	2 September 2008
8 February 2009	8 April 2009	2.14940	9.8	26 May 2009	17 November 2009
7 May 2010	27 June 2010	1.75731	9.0	18 August 2010	22 February 2011
15 October 2011	28 November 2011	1.24553	8.0	3 January 2012	4 August 2012
16 January 2013	16 March 2013	2.04489	9.6	4 May 2013	26 October 2013
8 April 2014	31 May 2014	1.98596	9.5	21 July 2014	15 January 2015
14 August 2015	2 October 2015	1.21174	7.9	6 November 2015	27 June 2016
25 December 2016	19 February 2017	1.84200	9.2	9 April 2017	4 October 2017
12 March 2018	7 May 2018	2.12485	9.8	26 June 2018	18 December 2018
23 June 2019	12 August 2019	1.39369	8.2	28 September 2019	5 May 2020
1 December 2020	21 January 2021	1.56826	8.4	9 March 2021	11 September 2021

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For other objects and regions, see: Binary asteroids, Asteroid moons and the Solar system

For a complete listing, see: List of asteroids. For pronunciation, see: Pronunciation of asteroid names.