13 Egeria

Template:Short description {{#invoke:other uses|otheruses}} Template:Use dmy dates Template:Infobox planet

13 Egeria is a large main-belt G-type asteroid.<ref name="LPSC98"/> It was discovered by Annibale de Gasparis on 2 November 1850. Egeria was named by Urbain Le Verrier, whose computations led to the discovery of Neptune, after the mythological nymph Egeria of Aricia, Italy, the wife of Numa Pompilius, second king of Rome.<ref name="Schmadel2003"/>

History

Egeria was discovered on the evening of 2 November 1850 by Italian astronomer Annibale de Gasparis at the Astronomical Observatory of Capodimonte.<ref name="deGasparis1850"/><ref name="Hind"/>Template:Rp Whereas de Gasparis's previous two discoveries—10 Hygiea and 11 Parthenope—were identified by comparison with the Berlin Academy star charts, Egeria was identified using his own ecliptic charts intended for finding new celestial objects.<ref name="Airy1851"/>Template:Rp<ref name="Hind"/>Template:Rp Egeria's discovery was announced in December 1850 by astronomer Benjamin A. Gould through the Astronomical Journal.<ref name="Gould1850"/> Following the discovery, de Gasparis delegated the naming rights of the asteroid to Urbain Le Verrier. Le Verrier chose to name the asteroid after Egeria, a mythological nymph and councillor of Numa Pompilius.<ref name="Hind"/>Template:Rp

Upon its discovery, both de Gasparis and Gould labelled Egeria as a new planet.<ref name="deGasparis1850"/><ref name="Gould1850"/> However, by the mid-1800s, the classification and terminology of the asteroids were quickly evolving.<ref name="minorplanets"/> Soon after Egeria's discovery, other astronomers described it as an "asteroid"<ref name="Gould1852"/> or a "minor planet".<ref name="astrovocab"/>Template:Rp Throughout the latter half of the 19th century, the terms "asteroid" and "minor planet" became favored,<ref name="minorplanets"/> although some publications continued to label Egeria and other asteroids as planets.<ref name="minorplanets"/><ref name="Airy1869"/>Template:Rp

In 1851, de Gasparis announced his chosen symbol for Egeria—that of a buckler. However, Gould had apparently not seen the announcement, and in an 1852 table of asteroid symbols he left Egeria's blank.<ref name="astronomy-unicode"/>Template:Rp<ref name="Gould1852"/> No mention of a star was made, though in 1852 John Russell Hind included one in his drawn symbol for Egeria: (U+1CEC6 𜻆 in Unicode 17.0). The symbol is sometimes depicted with a round form (),<ref name="astronomy-unicode"/>Template:Rp though only Hind's form was encoded.<ref name="Unicode-1CEC0">Template:Cite web</ref> As the number of asteroids assigned a symbol grew in number through the mid-1800s, the practicality of assigning each a unique astronomical symbol was questioned. In 1851, astronomer Johann Franz Encke proposed an alternative system of a number—denoting the object's order of discovery—inscribed in a circle. For Egeria, this would be ⑬.<ref name="minorplanets"/><ref name="Gould1852"/> This system was quickly adopted by astronomers, though eventually astronomers switched from an inscribed circle to parentheses and eventually a bare number<ref name="minorplanets"/>—hence (13) Egeria or 13 Egeria in modern notation.<ref name="MPC-object"/><ref name=jpldata/>

Physical properties

OCCULT4 visualization of 13 Egeria occultation event of January 22, 2008

Egeria occulted a star on January 8, 1992. Its disc was determined to be quite circular (217×196 km). On January 22, 2008, it occulted another star, and this occultation was timed by several observers in New Mexico and Arizona, coordinated by the IOTA Asteroid Occultation Program.<ref name=2008a/> The result showed that Egeria presented an approximately circular profile to Earth of 214.8×192 km, well in agreement with the 1992 occultation.Template:Citation needed It has also been studied by radar.<ref name="detected"/>

In 1988 a search for satellites or dust orbiting this asteroid was performed using the UH88 telescope at the Mauna Kea Observatories, but the effort came up empty.<ref name="Gradie1988"/> Spectral analysis of Egeria shows it to be unusually high in water content, 10.5–11.5% water by mass.<ref name="Rivkin2002"/>

File:13Egeria (Lightcurve Inversion).png

A three-dimensional model of 13 Egeria based on its light curve

See also

• Former classification of planets

External links

• Template:Cite web (displays Elong from Sun and V mag for 2011)
• Template:AstDys
• Template:JPL small body