5 Astraea

5 Astraea
	Lightcurve-based 3D-model of Astraea
Discovery
Discovered by	K. L. Hencke
Discovery site	Driesen Obs.
Discovery date	8 December 1845
Designations
MPC designation	(5) Astraea
Pronunciation	/æˈstriːə/
Named after	Astraea (Greek goddess)
Alternative designations	1969 SE
Minor planet category	main-belt · (middle); Astraea
Adjectives	Astraean
Symbol	(historical astronomical), (modern astrological)
Orbital characteristics
	Epoch 23 March 2018 (JD 2458200.5)
	Uncertainty parameter 0
Observation arc	171.93 yr (62,799 d)
Aphelion	3.0659 AU
Perihelion	2.0810 AU
Semi-major axis	2.5735 AU
Eccentricity	0.1914
Orbital period (sidereal)	4.13 yr (1,508 d) 4.13 yr (1,508 d)
Mean anomaly	186.83°
Mean motion	0° 14m 19.32s / day
Inclination	5.3677°
Longitude of ascending node	141.58°
Argument of perihelion	358.75°
Proper orbital elements
Proper semi-major axis	2.5761849 AU
Proper eccentricity	0.1980486
Proper inclination	4.5118628°
Proper mean motion	87.046396 deg / yr
Proper orbital period	4.13573 yr; (1510.574 d)
Precession of perihelion	52.210903 arcsec / yr
Precession of the ascending node	−57.357951 arcsec / yr
Physical characteristics
Dimensions	169 km × 125 km × 83 km
Mean diameter	125 km
Surface area	48 900 km2
Volume	920 000 km3
Mass	(2.716 ± 0.326/0.45)×1018 kg
Mean density	3.501 ± 0.420/0.581 g/cm3
Synodic rotation period	0.700 04 d (16.801 h)
Equatorial rotation velocity	6.49 m/s
North pole right ascension	115°/310° ± 5°
North pole declination	55° ± 5°
Geometric albedo	0.227
Spectral type	S
Apparent magnitude	8.74 to 12.89
Absolute magnitude (H)	6.85
Angular diameter	0.15" 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.^[4]

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.^[10]

Hencke's symbol for Astraea is an inverted anchor, in the pipeline for Unicode 17.0 as U+1F778 🝸 (),^[11]^[12] though given Astraea's role with justice and precision, it is perhaps a stylized set of scales, or a typographic substitute for one.^[13]^[14] This symbol is no longer used. The astrological symbol is a percent sign, encoded specifically at U+2BD9 ⯙.^[15] 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.^[16] 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 demotion of the four original asteroids (which were regarded as planets at the time)^[16] 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.

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.^[17]

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.

Notes

^ ^a ^b ^c Calculated based on the known parameters
^ Assuming a diameter of 114 ± 4 km.

References

^ ^a ^b "5 Astraea". Minor Planet Center. Retrieved 1 June 2018.
^ "Astraea". Lexico UK English Dictionary. Oxford University Press. Archived from the original on 22 March 2020.
^ 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.
^ ^a ^b ^c "JPL Small-Body Database Browser: 5 Astraea" (2017-11-22 last obs.). Jet Propulsion Laboratory. Retrieved 1 June 2018.
^ "Asteroid (5) Astraea – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 25 May 2018.
^ "AstDyS-2 Astraea Synthetic Proper Orbital Elements". Department of Mathematics, University of Pisa, Italy. Retrieved 1 October 2011.
^ ^a ^b ^c ^d 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.
^ ^a ^b 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.
^ 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.
^ "Dawn Community". NASA. Archived from the original on 21 May 2009. Retrieved 17 April 2009.
^ Bala, Gavin Jared; Miller, Kirk (18 September 2023). "Unicode request for historical asteroid symbols" (PDF). unicode.org. Unicode. Retrieved 26 September 2023.
^ Unicode. "Proposed New Characters: The Pipeline". unicode.org. The Unicode Consortium. Retrieved 6 November 2023.
^ 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.
^ Schmadel, Lutz D. (2003). Dictionary of Minor Planet Names. Springer. pp. 15–18. ISBN 978-0-354-06174-2.
^ Faulks, David (28 May 2016). "L2/16-080: Additional Symbols for Astrology" (PDF).
^ ^a ^b "The Planet Hygea". spaceweather.com. 1849. Archived from the original on 9 April 2008. Retrieved 18 April 2008.
^ 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.