5 Astraea

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This article is about the asteroid. For other uses, see Astraea (disambiguation).
5 Astraea
File:5 Astraea.png
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/[2]
Named after
Astraea (Greek goddess)[3]
1969 SE
main-belt[1][4] · (middle)
Astraea[5]
AdjectivesAstraean
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
Eccentricity0.1914
4.13 yr (1,508 d)
186.83°
0° 14m 19.32s / day
Inclination5.3677°
141.58°
358.75°
Proper orbital elements[6]
2.5761849 AU
0.1980486
4.5118628°
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
Dimensions169 km × 125 km × 83 km[7]
125 km[7]
48 900 km2[a]
Volume920 000 km3[a]
Mass(2.716 ± 0.326/0.45)×1018 kg[8]
Mean density
3.501 ± 0.420/0.581 g/cm3[8][b]
0.700 04 d (16.801 h)[7]
Equatorial rotation velocity
6.49 m/s[a]
North pole right ascension
115°/310° ± 5°
North pole declination
55° ± 5°
0.227[9]
S
8.74 to 12.89
6.85
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

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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, encoded in Unicode 17.0 as U+1F778 🝸 (File:Astraea symbol (fixed width).svg),[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] it is simply shift-5 on the keyboard, because Astraea was the fifth asteroid discovered.[11] 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 reclassification of the four original asteroids (which were identified as planets at the time)[16], as it became apparent that these were only the largest of a new type of celestial body with thousands of members.

Characteristics

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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]

File:Moon and Asteroids 1 to 10.svg
File:AstraeaOrbit.png
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

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Notes

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

References

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