221 Eos

221 Eos is a large main-belt asteroid that was discovered by Austrian astronomer Johann Palisa on January 18, 1882, in Vienna. In 1884, it was named after Eos, the Greek goddess of the dawn, to honour the opening of a new observatory that was hoped to bring about a new dawn for Viennese astronomy.^[5]

221 Eos

3D model based on lightcurve data
Discovery
Discovered by	Johann Palisa
Discovery date	18 January 1882
Designations
MPC designation	(221) Eos
Pronunciation	/ˈiːɒs/[1]
Named after	Eos
Alternative designations	A882 BA
Minor planet category	Main belt (Eos)
Adjectives	Eoan /iːˈoʊ.ən/[2]
Orbital characteristics[3]
Epoch 31 July 2016 (JD 2457600.5)
Uncertainty parameter 0
Observation arc	130.21 yr (47561 d)
Aphelion	3.3249 AU (497.40 Gm)
Perihelion	2.69594 AU (403.307 Gm)
Semi-major axis	3.01044 AU (450.355 Gm)
Eccentricity	0.10447
Orbital period (sidereal)	5.22 yr (1907.8 d)
Average orbital speed	17.16 km/s
Mean anomaly	66.5202°
Mean motion	0° 11m 19.284s / day
Inclination	10.880°
Longitude of ascending node	141.845°
Argument of perihelion	193.56°
Physical characteristics
Dimensions	103.87±3.6 km[3] 103.52 ± 5.60 km[4]
Mass	(5.87 ± 0.34) × 1018 kg[4]
Mean density	10.10 ± 1.74 g/cm3[4]
Synodic rotation period	10.443 h (0.4351 d)
Geometric albedo	0.1400±0.010
Spectral type	K
Absolute magnitude (H)	7.67

The asteroid is orbiting the Sun with a semimajor axis of 3.01 AU, a period of 5.22 years, and an eccentricity of 0.1. The orbital plane is inclined by 10.9° to the plane of the ecliptic. It has a mean cross-section of 104 km,^[3] and is spinning with a rotation period of 10.4 hours. Based upon its spectral characteristics, this object is classified as a K-type asteroid. The orbital properties show it to be a member of the extensive Eos asteroid family, which is named after it.^[6] The spectral properties of the asteroid suggest it may have come from a partially differentiated parent body.^[7]