5 Astraea () is an

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

in the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...

. This object is orbiting the Sun at a distance of with a period of and an

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values be ...

of 0.19. The

orbital plane The orbital plane of a revolving body is the geometric plane in which its orbit lies. Three non-collinear points in space suffice to determine an orbital plane. A common example would be the positions of the centers of a massive body (host) a ...

is inclined at an angle of 5.37° to the

plane of the ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. From the perspe ...

. 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 Nickel is a chemical element; it has 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 slo ...

–

iron Iron is a chemical element; it has symbol Fe () 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, forming much of Earth's o ...

with

silicates 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 also used for an ...

magnesium Magnesium is a chemical element; it has Symbol (chemistry), 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 ...

and

. It is an S-type asteroid in the Tholen classification 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 astronomers, German astronomer. Biography Hencke was born ...

and named for

Astraea In ancient Greek religion and mythology, Astraea (; ), also spelled Astrea or Astria, is a daughter of Astraeus and Eos. She is the virgin goddess of justice, innocence, purity, and precision. She is closely associated with the Greek goddess of ...

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

6 Hebe 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), Hebe does not rank among the top twenty asteroids by volume. This high bu ...

. 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 (mytho ...

when he stumbled on Astraea. The King of

Prussia Prussia (; ; Old Prussian: ''Prūsija'') was a Germans, German state centred on the North European Plain that originated from the 1525 secularization of the Prussia (region), Prussian part of the State of the Teutonic Order. For centuries, ...

awarded him an annual pension of 1200

marks Marks may refer to: Business * Mark's, a Canadian retail chain * Marks & Spencer, a British retail chain * Collective trade marks A collective trademark, collective trade mark, or collective mark is a trademark owned by an organization (such ...

for the discovery. Hencke's symbol for Astraea is an inverted anchor, in the pipeline for Unicode 17.0 as U+1F778 🝸 (), 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 a percent sign, encoded specifically at U+2BD9 ⯙: it is simply shift-5 on the keyboard, because Astraea was the fifth asteroid discovered. 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, 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) 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 equinox (celestial coordinates), March equinox to the (hour circle of the) point in questio ...

115° or 310° and

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. The declination angle is measured north (positive) or ...

55°, 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 orbita ...

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), ''Stellar'' (magazine), an Irish lifestyle and fashion magazine * Stellar Loussier, a character fro ...

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

Notes

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

Notes

References

External links