61 Danaë

61 Danaë (/ˈdæneɪ.iː/) is a stony (S-type) asteroid in the outer asteroid belt's background population, approximately 84 kilometer in diameter. It was discovered by French astronomer Hermann Goldschmidt on 9 September 1860, from his balcony in Paris, France.^[17] Goldschmidt was ill when asked to name the asteroid, and requested his fellow asteroid-hunter Robert Luther to name it instead. Luther chose to name it after Danaë, the mother of Perseus in Greek mythology.^[3] Danaë was the first asteroid to have a diacritical character in its official name.

61 Danaë

Discovery[1]
Discovered by	H. Goldschmidt
Discovery site	Paris
Discovery date	9 September 1860
Designations
MPC designation	(61) Danaë
Pronunciation	/ˈdæneɪ.iː/[2]
Named after	Danaë (Greek mythology)[3]
Alternative designations	1953 RL1 · A917 SM
Minor planet category	main-belt · (outer)[4] background[5]
Adjectives	Danaëan /dæneɪˈiːən/[6]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc	151.67 yr (55,398 days)
Aphelion	3.4798 AU
Perihelion	2.4840 AU
Semi-major axis	2.9819 AU
Eccentricity	0.1670
Orbital period (sidereal)	5.15 yr (1,881 days)
Mean anomaly	157.11°
Mean motion	0° 11m 29.04s / day
Inclination	18.212°
Longitude of ascending node	333.72°
Argument of perihelion	12.695°
Physical characteristics
Dimensions	82.04±4.3 km[7] 82.52±2.73 km[8] 83.56±1.02 km[9] 85.125±1.962 km[10] 85.937±2.151 km[11] 91.00±3.50 km[12]
Mass	(2.89±2.78)×1018 kg[8]
Mean density	9.81±9.49 g/cm3[8]
Synodic rotation period	11.45 h[13] 11.547±0.001 h[14]
Geometric albedo	0.181±0.034[12] 0.203±0.014[11] 0.2065±0.0472[10] 0.216±0.006[9] 0.2224±0.025[7]
Spectral type	Tholen = S[1] SMASS = S[1][4] B–V = 0.852[1] U–B = 0.402[1]
Absolute magnitude (H)	7.56±0.10[15] · 7.68[1][4][7][9][10][12] · 7.78±0.25[16]

The asteroid is orbiting the Sun with a period of 5.15 years and is rotating on its axis once every 11.45 hours. In 1985, a study of lightcurve data suggested that Danaë may have a moon. If so, the main body would be an ellipsoid measuring 85 km × 80 km × 75 km (53 mi × 50 mi × 47 mi), and the moon would orbit 101 kilometres (63 mi) away, measuring 55 km × 30 km × 30 km (34 mi × 19 mi × 19 mi). The density of both would be 1.1 g/cm³.^[18]