Astronomy:5 Astraea

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5 Astraea The historic planetary symbol for 5 Astraea (historical astronomical), The modern astrological symbol for 5 Astraea (modern astrological)
Images of 5 Astraea (bottom) compared with 3D models based on lightcurve data (top)
Discovery[1]
Discovered byK. L. Hencke
Discovery siteDriesen Obs.
Discovery date8 December 1845
Designations
(5) Astraea
Pronunciation/æˈstriːə/[5]
Named afterAstraea (Greek goddess)[2]
1969 SE
Minor planet categorymain-belt[1][3] · (middle)
Astraea[4]
AdjectivesAstraean
Orbital characteristics[3]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc171.93 yr (62,799 d)
|{{{apsis}}}|helion}}3.0659 AU
|{{{apsis}}}|helion}}2.0810 AU
2.5735 AU
Eccentricity0.1914
Orbital period4.13 yr (1,508 d)
Mean anomaly186.83°
Mean motion0° 14m 19.32s / day
Inclination5.3677°
Longitude of ascending node141.58°
358.75°
Proper orbital elements[6]
Proper semi-major axis2.5761849 AU
Proper eccentricity0.1980486
Proper inclination4.5118628°
Proper mean motion87.046396 deg / yr
4.13573 yr
(1510.574 d)
Precession of perihelion52.210903 arcsec / yr
Precession of the ascending node−57.357951 arcsec / yr
Physical characteristics
Dimensions169 km × 125 km × 83 km[7]
Mean diameter125 km[7]
Surface area48 900 km2[lower-alpha 1]
Volume920 000 km3[lower-alpha 1]
MassTemplate:Nwr
Mean density3.501 ± 0.420/0.581 g/cm3[8][lower-alpha 2]
Rotation period0.700 04 d (16.801 h)[7]
Equatorial rotation velocity6.49 m/s[lower-alpha 1]
North pole right ascension115°/310° ± 5°
North pole declination55° ± 5°
Geometric albedo0.227[9]
S
Apparent magnitude9.0[10] to 13.0
Absolute magnitude (H)6.85
Angular diameter0.15" to 0.041"


5 Astraea (/æˈstriːə/) is an asteroid in the asteroid belt. This object is orbiting the Sun at a distance of 385 million kilometres (2.5735 AU) with a period of 4.13 yr and an orbital eccentricity of 0.19. The orbital plane is inclined at an angle of 5.37° to the plane of the ecliptic. It is spinning with a period of 16.8 h. The surface of Astraea is highly reflective and its composition is probably a mixture of nickel–iron with silicates of magnesium and iron. It is an S-type asteroid in the Tholen classification system.[3]

Discovery and name

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 1200 marks for the discovery.[11]

Hencke's symbol for Astraea is an inverted anchor, encoded in Unicode 17.0 as U+1F778 🝸 (),[12][13] 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] it is simply shift-5 on the keyboard, because Astraea was the fifth asteroid discovered.[12] 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, 8 more were discovered in the following 5 years, and 24 were found in the 5 years after that. The discovery of Astraea proved to be the starting point for the eventual reclassification of the four original asteroids (which were identified as planets at the time)[17], as it became apparent that these were only the largest of a new type of celestial body with thousands of members.

Characteristics

Photometry indicates prograde rotation, that the north pole points in the direction of right ascension 115° or 310° and declination 55°, with a 5° uncertainty.[7] This gives an axial tilt of about 33°.[citation needed] 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

Notes

  1. ↑ 1.0 1.1 1.2 Calculated based on the known parameters
  2. ↑ Assuming a diameter of 114 ± 4 km.

References

  1. ↑ 1.0 1.1 "5 Astraea". Minor Planet Center. https://www.minorplanetcenter.net/db_search/show_object?object_id=5. 
  2. ↑ 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. 
  3. ↑ 3.0 3.1 3.2 "JPL Small-Body Database Browser: 5 Astraea". Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2000005. 
  4. ↑ "Asteroid (5) Astraea – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. https://newton.spacedys.com/astdys/index.php?n=5&pc=1.1.6. 
  5. ↑ "Astraea". Astraea. Oxford University Press. http://www.lexico.com/definition/Astraea. 
  6. ↑ "AstDyS-2 Astraea Synthetic Proper Orbital Elements". Department of Mathematics, University of Pisa, Italy. https://newton.spacedys.com/astdys/index.php?pc=1.1.6&n=5. 
  7. ↑ 7.0 7.1 7.2 7.3 M. J. López-Gonzáles; E. Rodríguez (2005). "Lightcurves and poles of seven asteroids". Planetary and Space Science 53: 1147. doi:10.1016/j.pss.2005.04.010. https://ui.adsabs.harvard.edu/abs/2005P%26SS...53.1147L/abstract. 
  8. ↑ Fienga, A.; Avdellidou, C.; Hanuš, J. (February 2020). "Asteroid masses obtained with INPOP planetary ephemerides". Monthly Notices of the Royal Astronomical Society 492 (1). doi:10.1093/mnras/stz3407. https://academic.oup.com/mnras/article/492/1/589/5658701. 
  9. ↑ 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. https://sbnarchive.psi.edu/pds3/iras/IRAS_A_FPA_3_RDR_IMPS_V6_0/data/diamalb.tab. Retrieved 22 October 2019. 
  10. ↑ Perihelic opposition
  11. ↑ "Dawn Community". NASA. http://dawn.jpl.nasa.gov/DawnCommunity/flashbacks/fb_09.asp. 
  12. ↑ 12.0 12.1 Bala, Gavin Jared; Miller, Kirk (18 September 2023). "Unicode request for historical asteroid symbols". Unicode. https://www.unicode.org/L2/L2023/23207-historical-asteroids.pdf. 
  13. ↑ "Alchemical Symbols". The Unicode Consortium. 2025. https://www.unicode.org/charts/PDF/U1F700.pdf. 
  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. https://books.google.com/books?id=ZM8DAAAAMAAJ&pg=PA406. "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 (2016-05-28). "L2/16-080: Additional Symbols for Astrology". https://www.unicode.org/L2/L2016/16080r-add-astrology.pdf. 
  17. ↑ 17.0 17.1 "The Planet Hygea". spaceweather.com. 1849. http://spaceweather.com/swpod2006/13sep06/Pollock1.jpg. 
  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". Icarus 214 (2): 652–670. doi:10.1016/j.icarus.2011.03.016. Bibcode: 2011Icar..214..652D. http://astro.troja.mff.cuni.cz/projects/asteroids3D/download/durech_et_al_2011_occ_paper.pdf. Retrieved 26 January 2012. 



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