Spica
From Wikipedia, the free encyclopedia
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Virgo |
| Pronunciation | /ˈspaɪkə/ |
| Right ascension | 13h 25m 11.6s |
| Declination | −11° 09' 41" |
| Apparent magnitude (V) | +1.04 |
| Characteristics | |
| Spectral type | B1III-IV/B2V |
| U-B color index | −0.93 |
| B-V color index | −0.13[citation needed] |
| Variable type | β Cep, Rotating ellipsoid |
| Astrometry | |
| Radial velocity (Rv) | +1.0 km/s |
| Proper motion (μ) | RA: −42.50 mas/yr Dec.: −31.73 mas/yr |
| Parallax (π) | 12.44 ± 0.86 mas |
| Distance | 260 ± 20 ly (80 ± 6 pc) |
| Absolute magnitude (MV) | −3.55 |
| Details | |
| Mass | 11/7 M☉ |
| Radius | 7.8/4.0 R☉ |
| Luminosity | 13,400/1,700 L☉ |
| Temperature | 22,400/18,500 K |
| Other designations | |
Spica (α Vir / α Virginis / Alpha Virginis) is the brightest star in the constellation Virgo, and the 15th brightest star in the nighttime sky. It is 260 light years distant from Earth. A blue giant, it is a variable of the Beta Cephei type.
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[edit] Observation history
Spica is believed to be the star that provided Hipparchus with the data which enabled him to discover precession of the equinoxes.[1] A temple to Menat (an early Hathor) at Thebes was oriented with reference to Spica when it was constructed in 3200 BC and, over time, precession resulted in a slow but noticeable change in the location of Spica relative to the temple.[2] Nicolaus Copernicus made many observations of Spica with his home-made triquetrum for his researches on precession.[3]
[edit] Characteristics
Spica is the brightest of the rotating ellipsoidal variables. Its apparent magnitude varies between +0.92 and +1.04, with a period of 4.0142 days. This slight dip in magnitude is barely noticeable visually. It is also a variable of the Beta Cephei type. Spica has a luminosity about 2,300 times that of the Sun. Spica is a double star, but the distance between the two stars is so small that it distorts the image, and makes the two stars seem like one, with very slight brightness variations.
[edit] Visibility
Located close to the ecliptic, Spica can be occulted by the Moon and sometimes by the planets. The last planetary occultation of Spica occurred when Venus passed in front of the star (as seen from Earth) on November 10, 1783. The next occultation will occur September 2, 2197, when Venus again passes in front of Spica. The Sun passes a little more than 2º north of Spica around October 16 every year.
An easy way to find Spica is to follow the arc of the handle of the Big Dipper to Arcturus, and then continue on the same distance to Spica ("follow the arc to Arcturus and speed on to Spica").
[edit] Etymology and cultural significance
The name Spica derives from Latin spīca virginis "Virgo's ear of grain" (usually wheat). In Chinese astronomy, the star is known as Jiao Xiu 1 (角宿一) in Jiao Xiu, one of the Chinese constellations. In Hindu astronomy, Spica corresponds to the Nakshatra Chitra. The 17th century German astronomer Bayer and others referred to the star as Arista.
Medieval names include Azimech, from Arabic as-simak al-a'zal "the Undefended", and Alarph, Arabic for "the Grape Gatherer".
In medieval astrology, it was a Behenian fixed star, associated with the emerald and sage. In his De Occulta Philosophia, Cornelius Agrippa attributes its kabbalistic symbol 
to Hermes Trismegistus.
Spica was used in the novel Pushing Ice by Alastair Reynolds as the distant star to which the protagonists are carried by alien technology.
The Japanese manga and series Twin Spica was named after the star. Spica is two stars that circle each other, though from a distance they appear as one, which parallels the series' running theme of friendship.
[edit] References
- ^ Evans, James (1998). The History and Practice of Ancient Astronomy. Oxford University Press. pp. 259. ISBN 0195095391. http://books.google.com.au/books?id=nS51_7qbEWsC&pg=PA259&lpg=PA259&dq=spica+hipparchus&source=bl&ots=c1dkQmjFl8&sig=I1zqqn_pb4V65A5Rlzx7FKA9AuU&hl=en&ei=zMrGSeiaI5iy6wP5rqG6Bw&sa=X&oi=book_result&resnum=6&ct=result.
- ^ Allen, Richard Hinckley (2003). Star Names and Their Meanings. Kessinger Publishing. pp. 468. ISBN 0766140288. http://books.google.com.au/books?id=_GUDis0bETgC&pg=PA468&lpg=PA468&dq=spica+thebes+temple+menat&source=bl&ots=6SYdIUUyKg&sig=f3v7K4DaebtOi1kDByXpczmzhkg&hl=en&ei=bszGSfzYI5iVkAWp2-nNDA&sa=X&oi=book_result&resnum=10&ct=result.
- ^ Rufus, W. Carl (April 1943). "Copernicus, Polish Astronomer, 1473–1543". The Journal of the Royal Astronomical Society of Canada 37 (4): 134. Bibcode: 1943JRASC..37..129R. http://articles.adsabs.harvard.edu//full/1943JRASC..37..129R/0000129.000.html.
[edit] External links
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