5 Astraea

5 Astraea (Template:IPAc-en) is an asteroid in the asteroid belt. This object is orbiting the Sun at a distance of Template:Convert with a period of Template:Cvt 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.<ref name="jpldata" />

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.<ref>Template:Cite web</ref>

Hencke's symbol for Astraea is an inverted anchor, encoded in Unicode 17.0 as U+1F778 🝸 (File:Astraea symbol (fixed width).svg),<ref name=astunicode>Template:Cite web</ref><ref name="Unicode-1F700">Template:Cite web</ref> though given Astraea's role with justice and precision, it is perhaps a stylized set of scales, or a typographic substitute for one.<ref name=berlin-1845> Template:Cite book</ref><ref name=schmadel>Template:Cite book</ref> This symbol is no longer used. The astrological symbol is a percent sign, encoded specifically at U+2BD9 ⯙:<ref name="L216080">Template:Cite web</ref> it is simply shift-5 on the keyboard, because Astraea was the fifth asteroid discovered.<ref name=astunicode/> 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.<ref name=18planets>Template:Cite web</ref> 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)<ref name=18planets/>, 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.<ref name=Lopez-Gonzales /> This gives an axial tilt of about 33°.Template:Cn 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 Template:Nowrap.<ref name="Ďurech2011">Template:Cite journal</ref>

See also

• Former classification of planets

Notes

<references group="lower-alpha" />

External links

• 2 Telescope images of 5 Astraea
• MNRAS 7 (1846) 27
• Physical characteristics of (5) Astraea at the Small Bodies Data Ferret
• Discovery Circumstances: Numbered Minor Planets (1)-(5000) – Minor Planet Center
• Dictionary of Minor Planet Names, Google books
• Template:AstDys
• Template:JPL small body