Astraea () (

minor planet designation A formal minor-planet designation is, in its final form, a number–name combination given to a minor planet (asteroid, centaur, trans-Neptunian object and dwarf planet but not comet). Such designation always features a leading number (catalog or ...

: 5 Astraea) is an

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

in the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...

. Its surface is highly reflective and its composition is probably a mixture of

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...

–

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

with

silicates In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

and

. It is an

S-type asteroid S-type asteroids are asteroids with a spectral type that is indicative of a siliceous (i.e. stony) mineralogical composition, hence the name. They have relatively high density. Approximately 17% of asteroids are of this type, making it the second ...

in the

Tholen classification An asteroid spectral type is assigned to asteroids based on their emission spectrum, color, and sometimes albedo. These types are thought to correspond to an asteroid's surface composition. For small bodies that are not internally differentiated ...

system.

Discovery and name

Astraea was the fifth asteroid discovered, on 8 December 1845, by

Karl Ludwig Hencke Karl Ludwig Hencke (8 April 1793 – 21 September 1866) was a German amateur astronomer and discoverer of minor planets. He is sometimes confused with Johann Franz Encke, another German astronomer. Biography Hencke was born in Driesen, Branden ...

and named for

Astraea Astraea, Astrea or Astria ( grc, Ἀστραία, Astraía; "star-maiden" or "starry night"), in ancient Greek religion, is a daughter of Astraeus and Eos. She is the virgin goddess of justice, innocence, purity and precision. She is closely asso ...

, a Greek goddess of justice named after the stars. It was his first of two asteroid discoveries. The second was

6 Hebe Hebe (minor planet designation: 6 Hebe) is a large main-belt asteroid, containing around 0.5% of the mass of the belt. However, due to its apparently high bulk density (greater than that of the Moon or even Mars), Hebe does not rank among the to ...

. A German amateur astronomer and post office headmaster, Hencke was looking for

4 Vesta Vesta (minor-planet designation: 4 Vesta) is one of the largest objects in the asteroid belt, with a mean diameter of . It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, the ...

when he stumbled on Astraea. The King of

Prussia Prussia, , Old Prussian: ''Prūsa'' or ''Prūsija'' was a German state on the southeast coast of the Baltic Sea. It formed the German Empire under Prussian rule when it united the German states in 1871. It was ''de facto'' dissolved by an em ...

awarded him an annual pension of 1,200

marks Marks may refer to: Business * Mark's, a Canadian retail chain * Marks & Spencer, a British retail chain * Collective trade marks, trademarks owned by an organisation for the benefit of its members * Marks & Co, the inspiration for the novel '' ...

for the discovery. Hencke's symbol for Astraea is an inverted anchor, though given Astraea's role with justice and precision, it is perhaps a stylized set of scales, or a typographic substitute for one. This symbol is no longer used. The astrological symbol is U+2BD9 ⯙ ( Astraea symbol (astrology)

), a stylized

percent sign The percent sign (sometimes per cent sign in British English) is the symbol used to indicate a percentage, a number or ratio as a fraction of 100. Related signs include the permille (per thousand) sign and the permyriad (per ten thousand) s ...

. 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. After the discovery of Astraea, five more were discovered during the 1840s, and 47 were found during the 1850s. 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) 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 Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point in question above the earth. When paired w ...

9 h 52 min,

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the ...

73° with a 5° uncertainty. This gives an

axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbi ...

of about 33°. With an apparent

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

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 Stellar means anything related to one or more stars (''stella''). The term may also refer to: Arts, entertainment, and media * ''Stellar'' (magazine), an Irish lifestyle and fashion magazine * Stellar Loussier, a character from ''Mobile Suit Gu ...

on 6 June 2008 allowed Astraea's diameter to be estimated; it was found to be .

References

External links

2 Telescope images of 5 Astraea

Physical characteristics of (5) Astraea
at the Small Bodies Data Ferret

– Minor Planet Center
Dictionary of Minor Planet Names
Google books * * {{DEFAULTSORT:000005 Astraea asteroids

S-type asteroids (SMASS) S-type asteroids (Tholen) 18451208

Discovery and name

Characteristics

See also

References

External links