Minorplanet: | yes |
5 Astraea | |
Symbol: | (historical astronomical), (modern astrological) |
Background: |
|
Discovered: | 8 December 1845 |
Mpc Name: | (5) Astraea |
Alt Names: | 1969 SE |
Pronounced: | [1] |
Adjectives: | Astraean |
Epoch: | 23 March 2018 (JD 2458200.5) |
Uncertainty: | 0 |
Observation Arc: | 171.93 yr (62,799 d) |
Perihelion: | 2.0810 AU |
Semimajor: | 2.5735 AU |
Eccentricity: | 0.1914 |
Period: | 4.13 yr (1,508 d) |
Mean Motion: | / day |
Inclination: | 5.3677° |
Asc Node: | 141.58° |
Arg Peri: | 358.75° |
P Orbit Ref: | [2] |
P Semimajor: | 2.5761849 |
P Eccentricity: | 0.1980486 |
P Inclination: | 4.5118628° |
P Mean Motion: | 87.046396 |
Perihelion Rate: | 52.210903 |
Node Rate: | −57.357951 |
Dimensions: | [3] |
Mean Diameter: | 125 km |
Surface Area: | 48 900 km2 |
Volume: | 920 000 km3 |
Density: | 3.501 ± 0.420/0.581 g/cm |
Rotation: | 0.700 04 d (16.801 h) |
Rot Velocity: | 6.49 m/s |
Right Asc North Pole: | 115°/310° ± 5° |
Declination: | 55° ± 5° |
Spectral Type: | S |
Magnitude: | 8.74 to 12.89 |
Abs Magnitude: | 6.85 |
Albedo: | 0.227 |
Angular Size: | 0.15" to 0.041" |
5 Astraea is an asteroid in the asteroid belt. This object is orbiting the Sun at a distance of 2.57350NaN0 with a period of 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.
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.[4]
Hencke's symbol for Astraea is an inverted anchor, in the pipeline for Unicode 17.0 as U+1F778,[5] [6] though given Astraea's role with justice and precision, it is perhaps a stylized set of scales, or a typographic substitute for one.[7] [8] This symbol is no longer used. The astrological symbol is a percent sign, encoded specifically at U+2BD9 ⯙.[9] 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.[10] 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)[10] 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 115° or 310° and declination 55°, with a 5° uncertainty. 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 .[11]