221 Eos

{{Short description|Asteroid in the Asteroid belt}}

{{Infobox planet

| minorplanet=yes

|image=000221-asteroid shape model (221) Eos.png

|caption=3D model based on lightcurve data

| background=#D6D6D6

| name=221 Eos

| pronounce={{IPAc-en|ˈ|iː|ɒ|s}}Noah Webster (1884) A Practical Dictionary of the English Language

| discoverer=Johann Palisa

| discovered=18 January 1882

| mpc_name=(221) Eos

| alt_names=A882 BA

| adjective=Eoan {{IPAc-en|iː|ˈ|oʊ|.|ən}}{{OED|Eoan}}

| named_after=Eos

| mp_category=Main belt (Eos)

| epoch=31 July 2016 (JD 2457600.5)

| semimajor={{Convert|3.01044|AU|Gm|abbr=on}}

| perihelion={{Convert|2.69594|AU|Gm|abbr=on}}

| aphelion={{Convert|3.3249|AU|Gm|abbr=on|lk=on}}

| eccentricity=0.10447

| period=5.22 yr (1907.8 d)

| inclination=10.880°

| asc_node=141.845°

| arg_peri=193.56°

| mean_anomaly=66.5202°

| avg_speed=17.16 km/s

| dimensions={{val|103.87|3.6|ul=km}}
103.52 ± 5.60 km

| mass={{nowrap|(5.87 ± 0.34) × 10¹⁸ kg}}

| density=10.10 ± 1.74 g/cm³

| rotation={{Convert|10.443|h|d|abbr=on|lk=on}}

| spectral_type=K

| abs_magnitude=7.67

| albedo={{val|0.1400|0.010}}

| single_temperature=

| mean_motion={{Deg2DMS|0.18869|sup=ms}} / day

| orbit_ref={{Cite web |url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=221;cad=1 |archive-url=https://web.archive.org/web/20200913164306/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=221;cad=1 |url-status=dead |archive-date=13 September 2020 |title=221 Eos |work=JPL Small-Body Database |publisher=NASA/Jet Propulsion Laboratory |access-date=12 May 2016}}

| observation_arc=130.21 yr (47561 d)

| uncertainty=0

}}

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.

The asteroid is orbiting the Sun with a semimajor axis of {{Val|3.01|ul=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, 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. The spectral properties of the asteroid suggest it may have come from a partially differentiated parent body.