5 Astraea

From Wikipedia, the free encyclopedia
Jump to: navigation, search
5 Astraea Astronomical symbol for 5 Astraea
Discovery
Discovered by Karl Ludwig Hencke
Discovery time December 8, 1845
Names
Other names 1969 SE
Group Main belt
Orbit
Reference date November 26, 2005 (JD 2453700.5)
Longest distance from the Sun 459.202 Gm (3.070 AU)
Shortest distance from the Sun 310.688 Gm (2.077 AU)
Longest distance from the center of its orbital path
("semi-major axis")
384.945 Gm (2.573 AU)
How egg-shaped its orbit is
("eccentricity")
0.193
How long it takes to complete an orbit 1507.676 d (4.13 a)
Average speed 18.39 km/s
Mean anomaly 194.442°
Angle above the reference plane
("inclination")
5.369°
Longitude of where it comes up through the reference plane 141.690°
Angle between its shortest distance from what it orbits around and where it comes up through the reference plane
("argument of periapsis")
357.530°
Size and Other Qualities
Measures 167×123×82 km[1][2]
Mass ~2.4×1018 kg
Average density ~2.7 g/cm³[3]
Gravity at its surface ~0.023 m/s²
Slowest speed able to escape into space
("escape velocity")
~0.062 km/s
How long it takes to turn around one time 0.700 03 d (16.801 h)[2]
How much light it reflects 0.227 (geometric)[1]
Avg. surface temp. ~167 K
max: 263 K (-10 °C)
Light-band group
("spectral type")
S-type asteroid
Seeming brightness
("apparent magnitude")
8.7 to 12.92
True brightness
("absolute magnitude")
6.85
Seeming size
("angular diameter")
0.15" to 0.041"

5 Astraea (written Astræa in the early literature) is a big main belt asteroid. Its surface is very reflective (bright) and what it's made of is probably a mixture of nickel-iron with magnesium- and iron-silicates. The adjectival form of the name, although unused, would be Astraean (which also designates a genus of star corals).

Size comparison: the first 10 asteroids profiled against Earth's Moon. Astrea is the fifth from the left.

Astraea was the fifth asteroid found, on December 8, 1845 by K. L. Hencke. It was his first of two asteroid discoveries. The second was 6 Hebe. An amateur astronomer and post office employee, Hencke was looking for 4 Vesta when he stumbled on Astraea. The King of Prussia awarded him with an annual pension of 300 US$ (1968 dollars) for the discovery.[4]

Photometry indicates prograde rotation, that the north pole points in the direction of right ascension 9 h 52 min, declination 73° with a 5° uncertainty.[2] This gives an axial tilt of about 33°.

Astrea is physically unremarkable but notable mainly because for 38 years (after the discovery of Vesta in 1807) it had been thought that there were only four asteroids. In terms of maximum brightness, it is indeed only the seventeenth brightest main belt asteroid, being fainter than 192 Nausikaa and even, at rare near-perihelion oppositions, the highly eccentric carbonaceous 324 Bamberga.

After the discovery of Astraea, thousands of other asteroids would follow. Indeed, the discovery of Astrea 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 biggest of a whole new type of celestial body.

There has been only one seen stellar occultation by Astraea (February 2, 1991).

References[change | change source]

  1. 1.0 1.1 Supplemental IRAS Minor Planet Survey
  2. 2.0 2.1 2.2 M. J. López-Gonzáles & E. Rodríguez Lightcurves and poles of seven asteroids, Planetary and Space Science, Vol. 53, p. 1147 (2005).
  3. G. A. Krasinsky et al. Hidden Mass in the Asteroid Belt, Icarus, Vol. 158, p. 98 (2002).
  4. "DAWN: A Journey to the Beginning of the Solar System". NASA: Jet Propulsion Laboratory; California Institute of Technology. http://dawn.jpl.nasa.gov/DawnCommunity/flashbacks/fb_09.asp. Retrieved 20 July 2013.

Other websites[change | change source]