5 Astraea

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5 Astraea
Lightcurve-based 3D-model of Astraea
Discovered byK. L. Hencke
Discovery siteDriesen Obs.
Discovery date8 December 1845
(5) Astraea
Named after
Astraea (Greek goddess)[3]
1969 SE
main-belt[1][4] · (middle)
SymbolThe historic planetary symbol for 5 Astraea (historical astronomical), The modern astrological symbol for 5 Astraea (modern astrological)
Orbital characteristics[4]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc171.93 yr (62,799 d)
Aphelion3.0659 AU
Perihelion2.0810 AU
2.5735 AU
4.13 yr (1,508 d)
0° 14m 19.32s / day
Proper orbital elements[6]
2.5761849 AU
87.046396 deg / yr
4.13573 yr
(1510.574 d)
Precession of perihelion
52.210903 arcsec / yr
Precession of the ascending node
−57.357951 arcsec / yr
Physical characteristics
Dimensions167 km × 123 km × 82 km[7]
Mean diameter
119 km[7]
48 300 km2[8]
Volume882 000 km3[8]
Mass2.9×1018 kg[9][10]
Mean density
~3.3 g/cm3
0.700 03 d (16.801 h)[7]
Equatorial rotation velocity
6.44 m/s[8]
8.74 to 12.89
0.15" to 0.041"

Astraea (/æˈstrə/) (minor planet designation: 5 Astraea) is an asteroid in the asteroid belt. Its surface is highly reflective and its composition is probably a mixture of nickeliron with silicates of magnesium and iron. It is an S-type asteroid in the Tholen classification system.[4]

Discovery and name[edit]

Astraea was the fifth asteroid discovered, on 8 December 1845, by Karl Ludwig Hencke and named for Astraea, a Greek goddess of justice named after the stars. It was his first of two asteroid discoveries. The second was 6 Hebe. A German amateur astronomer and post office headmaster, Hencke was looking for 4 Vesta when he stumbled on Astraea. The King of Prussia awarded him an annual pension of 1,200 marks for the discovery.[13]

Hencke's symbol for Astraea is an inverted anchor, U+2BD4 ⯔ (), though given Astraea's role with justice and precision, it is perhaps a stylized set of scales, or a typographic substitute for one.[14][15] This symbol is no longer used. The astrological symbol is a percent sign, encoded specifically at U+2BD9 ⯙.[16] The modern astronomical symbol is a simple encircled 5 (⑤).

For 38 years after the discovery of the fourth known asteroid, Vesta, in 1807, no further asteroids were discovered.[17] After the discovery of Astraea, five more were discovered during the 1840s, and 47 were found during the 1850s. The discovery of Astraea proved to be the starting point for the eventual demotion of the four original asteroids (which were regarded as planets at the time)[17] to their current status, as it became apparent that these four were only the largest of a new type of celestial body with thousands of members.


Photometry indicates prograde rotation, that the north pole points in the direction of right ascension 9 h 52 min, declination 73° with a 5° uncertainty.[7] This gives an axial tilt of about 33°. With an apparent magnitude of 8.7 (on a favorable opposition on 15 February 2016), it is only the seventeenth-brightest main-belt asteroid, and fainter than, for example, 192 Nausikaa or even 324 Bamberga (at rare near-perihelion oppositions).

An stellar occultation on 6 June 2008 allowed Astraea's diameter to be estimated; it was found to be 115 ± 6 km.[18]

Left: A size comparison of the first 10 numbered asteroids profiled against Earth's Moon.
Right: The orbit of 5 Astraea in white compared with those of Earth, Mars and Jupiter.

See also[edit]


  1. ^ a b "5 Astraea". Minor Planet Center. Retrieved 1 June 2018.
  2. ^ "Astraea". Lexico UK English Dictionary. Oxford University Press. Archived from the original on 22 March 2020.
  3. ^ Schmadel, Lutz D. (2007). "(5) Astraea". Dictionary of Minor Planet Names – (5) Astraea. Springer Berlin Heidelberg. p. 15. doi:10.1007/978-3-540-29925-7_6. ISBN 978-3-540-00238-3.
  4. ^ a b c "JPL Small-Body Database Browser: 5 Astraea" (2017-11-22 last obs.). Jet Propulsion Laboratory. Retrieved 1 June 2018.
  5. ^ "Asteroid (5) Astraea – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 25 May 2018.
  6. ^ "AstDyS-2 Astraea Synthetic Proper Orbital Elements". Department of Mathematics, University of Pisa, Italy. Retrieved 1 October 2011.
  7. ^ a b c d M. J. López-Gonzáles & E. Rodríguez Lightcurves and poles of seven asteroids, Planetary and Space Science, Vol. 53, p. 1147 (2005).
  8. ^ a b c Calculated based on the known parameters
  9. ^ Michalak, G. (2001). "Determination of asteroid masses". Astronomy & Astrophysics. 374 (2): 703–711. Bibcode:2001A&A...374..703M. doi:10.1051/0004-6361:20010731.
  10. ^ (Mass estimate of Astra 0.015 / Mass of Ceres 4.75) * Mass of Ceres 9.43E+20 = 2.977E+18
  11. ^ Michalak2001 (Table 6) assumed masses of perturbing asteroids used in calculations of perturbations of the test asteroids.
  12. ^ Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System. 12: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode:2004PDSS...12.....T. Retrieved 22 October 2019.
  13. ^ "Dawn Community". NASA. Archived from the original on 21 May 2009. Retrieved 17 April 2009.
  14. ^ Bericht über die zur Bekanntmachung geeigneten Verhandlungen der Königl. Preuss. Akademie der Wissenschaften zu Berlin. Deutsche Akademie der Wissenschaften zu Berlin; Königlich Preussische Akademie der Wissenschaften zu Berlin. 1845. p. 406. Der Planet hat mit Einwilligung des Entdeckers den Namen Astraea erhalten, und sein Zeichen wird nach dem Wunsche des Hr. Hencke ein umgekehrter Anker sein.
  15. ^ Schmadel, Lutz D. (2003). Dictionary of Minor Planet Names. Springer. pp. 15–18. ISBN 978-0-354-06174-2.
  16. ^ Faulks, David (28 May 2016). "L2/16-080: Additional Symbols for Astrology" (PDF).
  17. ^ a b "The Planet Hygea". spaceweather.com. 1849. Archived from the original on 9 April 2008. Retrieved 18 April 2008.
  18. ^ Ďurech, Josef; Kaasalainen, Mikko; Herald, David; Dunham, David; Timerson, Brad; Hanuš, Josef; et al. (2011). "Combining asteroid models derived by lightcurve inversion with asteroidal occultation silhouettes" (PDF). Icarus. 214 (2): 652–670. arXiv:1104.4227. Bibcode:2011Icar..214..652D. doi:10.1016/j.icarus.2011.03.016. Archived from the original (PDF) on 3 March 2016. Retrieved 26 January 2012.

External links[edit]