5 Astraea

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5 Astraea Astronomical symbol for 5 Astraea
Discovered byKarl Ludwig Hencke
Discovery dateDecember 8, 1845
Other names1969 SE
CategoryMain belt
Reference date November 26, 2005 (JD 2453700.5)
Longest distance from the Sun459.202 Gm (3.070 AU)
Shortest distance from the Sun310.688 Gm (2.077 AU)
Longest distance from the center of its orbital path
("semi-major axis")
384.945 Gm (2.573 AU)
How long it takes to complete an orbit1507.676 d (4.13 a)
Average speed18.39 km/s
Mean anomaly194.442°
Angle above the reference plane
Size and other qualities
Measurements167×123×82 km[1][2]
Mass~2.4×1018 kg
Average density~2.7 g/cm³[3]
Surface gravity~0.023 m/s²
Escape velocity~0.062 km/s
Rotation period0.700 03 d (16.801 h)[2]
How much light it reflects0.227 (geometric)[1]
Avg. surface temp.~167 K
max: 263 K (-10 °C)
Spectral typeS-type asteroid
Seeming brightness
("apparent magnitude")
8.7 to 12.92
True brightness
("absolute magnitude")

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]

  • Yeomans, Donald K. "Horizons system". NASA JPL. Retrieved 2007-03-20. — Horizons can be used to obtain a current ephemeris
  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. Retrieved 20 July 2013.

Other websites[change | change source]