4797 Ako

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4797 Ako
Discovery [1]
Discovered by T. Nomura
K. Kawanishi
Discovery site Minami-Oda Obs.
Discovery date 30 September 1989
MPC designation 4797 Ako
Named after
Akō, Hyōgo
(Japanese city)[2]
1989 SJ · 1978 VY9
1985 QB4
main-belt · Nysa[3]
Orbital characteristics[1]
Epoch 27 June 2015 (JD 2457200.5)
Uncertainty parameter 0
Observation arc 37.02 yr (13,523 days)
Aphelion 2.8552 AU
Perihelion 1.9693 AU
2.4123 AU
Eccentricity 0.1836
3.75 yr (1,369 days)
Inclination 1.8127°
Physical characteristics
Dimensions 6.000±0.496 km[4]
4.19 km (calculated)[3]
4.085 h[5]
0.21 (assumed)[3]

4797 Ako, provisional designation 1989 SJ, is a stony asteroid from the inner regions of the asteroid belt, about 6 kilometers in diameter. It was discovered by the Japanese astronomers Toshiro Nomura and Kōyō Kawanishi at the Minami-Oda Observatory, Japan, on 30 September 1989.[6]

The asteroid orbits the Sun at a distance of 2.0–2.9 AU once every 3 years and 9 months (1,369 days). Its orbit shows an eccentricity of 0.18 and is tilted by 2 degrees to the plane of the ecliptic. It has a rotation period of 4.1 hours[5] and an albedo of 0.11, according to the U.S. Wide-field Infrared Survey Explorer survey with its subsequent NEOWISE mission.[4] However, the Collaborative Asteroid Lightcurve Link (CALL) assumes a higher albedo of 0.21, which is typical for a stony asteroid with a S-type spectrum. As a consequence, CALL calculates that the asteroid measures only 4 kilometers in diameter, as the higher the body's albedo (reflectivity), the lower its diameter for a given absolute magnitude (brightness).[1]

The minor planet was named after the city of Akō in the Hyōgo Prefecture, Japan, and its ancient castle on the Seto Inland Sea. Ako is famous for its salt production and the story of "Chushin-Gura", which shows the loyalty of samurais to their local lord. Three centuries ago 47 loyal samurais committed seppuku after avenging their master. The second discoverer, Kōyō Kawanishi, is an amateur astronomer and by profession a dentist, lives in Ako, where his private Minami-Oda observatory is located, and observes comets and minor planets.[2]


  1. ^ a b c d "JPL Small-Body Database Browser: 4797 Ako (1989 SJ)" (2015-11-14 last obs.). Jet Propulsion Laboratory. Retrieved December 2015. 
  2. ^ a b Schmadel, Lutz D. (2003). Dictionary of Minor Planet Names – (4797) Ako. Springer Berlin Heidelberg. p. 414. ISBN 978-3-540-29925-7. Retrieved December 2015. 
  3. ^ a b c d "LCDB Data for (4797) Ako". Asteroid Lightcurve Database (LCDB). Retrieved December 2015. 
  4. ^ a b c Mainzer, A.; Grav, T.; Masiero, J.; Hand, E.; Bauer, J.; Tholen, D.; et al. (November 2011). "NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results". The Astrophysical Journal 741 (2): 25. arXiv:1109.6407. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90. Retrieved December 2015. 
  5. ^ a b Bennefeld, Craig; Bass, Stephen; Blair, Ricco; Cunningham, Kendrick; Hill, Da'quia; McHenry, Michael; Maxwell, Lerone (October 2009). "Asteroid Lightcurve Analysis at Ricky Observatory". Bulletin of the Minor Planets (Section of the Association of Lunar and Planetary Observers) 36 (4): 147–148. Bibcode:2009MPBu...36..147B. ISSN 1052-8091. Retrieved December 2015. 
  6. ^ "4797 Ako (1989 SJ)". Minor Planet Center. Retrieved December 2015. 

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