5 Astraea
Large asteroid
From Wikipedia, the free encyclopedia
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]
Images of 5 Astraea (bottom) compared with 3D models based on lightcurve data (top) | |
| Discovery[1] | |
|---|---|
| Discovered by | K. L. Hencke |
| Discovery site | Driesen Obs. |
| Discovery date | 8 December 1845 |
| Designations | |
| (5) Astraea | |
| Pronunciation | /æˈstriːə/[2] |
Named after | Astraea (Greek goddess)[3] |
| 1969 SE | |
| main-belt[1][4] · (middle) Astraea[5] | |
| Adjectives | Astraean |
| Symbol | .svg){kind=small} (historical astronomical),  (modern astrological) |
| Orbital characteristics[4] | |
| 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 |
| 2.5735 AU | |
| Eccentricity | 0.1914 |
| 4.13 yr (1,508 d) | |
| 186.83° | |
| 0° 14m 19.32s / day | |
| Inclination | 5.3677° |
| 141.58° | |
| 358.75° | |
| Proper orbital elements[6] | |
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[7] |
| 125 km[7] | |
| 48 900 km2[a] | |
| Volume | 920 000 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 | |
| 9.0[10] to 13.0 | |
| 6.85 | |
| 0.15" to 0.041" | |
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 (.svg){kind=small}
),[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]
Right: The orbit of 5 Astraea in white compared with those of Earth, Mars and Jupiter.
