Spica (also known as 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.
Spica is believed to be the star that provided Hipparchus
with the data which enabled him to discover precession
of the equinoxes
. 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. Nicolaus Copernicus
made many observations of Spica with his home-made triquetrum
for his researches on precession.
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
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
. The next occultation will occur September 2
, 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").
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
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