The star's name is derived from theLatinspīca virginis "the virgin's ear of [wheat] grain". It was also anglicized asVirgin's Spike.[11] In 2016, theInternational Astronomical Union organized aWorking Group on Star Names (WGSN)[12] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[13] included a table of the first two batches of names approved by the WGSN; which includedSpica for this star. It is now so entered in the IAU Catalog of Star Names.[14]
In the Sumerian Starlist found in Uruk (Iraq), 3200-1500 BC, Spica (or a group of stars in Virgo) is called absinnu or šer'u 𒀊𒉆, "The Seed-Furrow".[15]
Other traditional names areAzimech/ˈæzɪmɛk/, fromArabic السماك الأعزلal-simāk al-ʼaʽzal 'the unarmedsimāk (of unknown meaning, cf.Eta Boötis);Alaraph, Arabic for 'the grape-gatherer' or 'gleaner', andSumbalet (Sombalet,Sembalet and variants), from Arabic سنبلةsunbulah "ear of grain".[11]
InChinese,角宿 (Jué Xiù), meaningHorn (asterism), refers to an asterism consisting of Spica andζ Virginis.[16] Consequently, theChinese name for Spica is角宿一 (Jué Xiù Yī, English:the First Star of Horn).[17]
Spica is the brightest star in the constellation of Virgo (lower left).
As one of the nearest massive binary star systems to the Sun, Spica has been the subject of many observational studies.[19]
Spica is believed to be the star that gaveHipparchus the data that led him to discover theprecession of the equinoxes.[20] Atemple toMenat (an earlyHathor) atThebes was oriented with reference to Spica when it was built in 3200 BC, and, over time, precession slowly but noticeably changed Spica's location relative to the temple.[21]Nicolaus Copernicus made many observations of Spica with his home-madetriquetrum for his researches on precession.[22][23]
Spica is 2.06 degrees from theecliptic[citation needed] and can beocculted by theMoon and sometimes byplanets. The last planetary occultation of Spica occurred whenVenus passed in front of the star (as seen fromEarth) on November 10, 1783. The next occultation will occur on September 2, 2197, when Venus again passes in front of Spica.[24] The Sun passes a little more than 2°north of Spica around October 16 every year, and the star'sheliacal rising occurs about two weeks later. Every 8 years, Venus passes Spica around the time of the star's heliacal rising, as in 2009 when it passed 3.5° north of the star on November 3.[25]
A method of finding Spica is to follow the arc of the handle of theBig Dipper (or Plough) to Arcturus, and then continue on the sameangular distance to Spica. This can be recalled by the mnemonic phrase, "arc to Arcturus and spike to Spica."[26][27]
Stars that can set (not in acircumpolar constellation for the viewer) culminate at midnight—noticeable where viewed away from any polar region experiencingmidnight sun—when atopposition, meaning they can be viewed from dusk until dawn. This applies to α Virginis on 12 April, in the currentastronomical epoch.[28]
Spica is a closebinary star whose components orbit each other every four days. They stay close enough together that they cannot be resolved as two stars through atelescope. The changes in the orbital motion of this pair results in aDoppler shift in theabsorption lines of their respectivespectra, making them a double-lined spectroscopic binary.[29] Initially, the orbital parameters for this system were inferred using spectroscopic measurements. Between 1966 and 1970, theNarrabri Stellar Intensity Interferometer was used to observe the pair and to directly measure the orbital characteristics and the angular diameter of the primary, which was found to be(0.90 ± 0.04) × 10−3 arcseconds, and the angular size of thesemi-major axis of the orbit was found to be only slightly larger at(1.54 ± 0.05) × 10−3 arcseconds.[8]
Spica is arotating ellipsoidal variable, which is a non-eclipsing close binary star system where the stars are mutually distorted through their gravitational interaction. This effect causes theapparent magnitude of the star system to vary by 0.03 over an interval that matches the orbital period. This slight dip in magnitude is barely noticeable visually.[30] Both stars rotate faster than their mutual orbital period. This lack of synchronization and the high ellipticity of their orbit may indicate that this is a young star system. Over time, the mutual tidal interaction of the pair may lead to rotational synchronization andorbit circularization.[31]
Alight curve for Spica, adapted from Tkachenkoet al. (2016)[9]
Spica is a polarimetric variable, first discovered to be such in 2016.[32] The majority of the polarimetric signal is the result of the reflection of the light from one star off the other (and vice versa). The two stars in Spica were the first ever to have their reflectivity (orgeometric albedo) measured. The geometric albedos of Spica A and B are, respectively, 3.61 percent and 1.36 percent,[33] values that are low compared to planets.
The MKspectral classification of Spica is typically considered to be an earlyB-type main-sequence star.[34] Individual spectral types for the two components are difficult to assign accurately, especially for the secondary due to theStruve–Sahade effect. TheBright Star Catalogue listed a spectral class of B1III-IV for the primary and B2V for the secondary,[35] but later studies have given various different values.[36][37]
The primary star has astellar classification of B1III-IV.[6] Theluminosity class matches the spectrum of a star that is midway between asubgiant and agiant star, and it is no longer amain-sequence star. The evolutionary stage has been calculated to be near or slightly past the end of the main-sequence phase.[37] This is a massive star with more than 10 times themass of the Sun and seven timesits radius. Thebolometric luminosity of the primary is about 20,500 times that of theSun, and nine times the luminosity of its companion.[9] The primary is one of the nearest stars to the Sun that has enough mass to end its life in aType II supernova explosion.[38][39] Since Spica has only recently left the main sequence, this event is not likely to occur for several more million years.
The primary is classified as aBeta Cepheivariable star that varies in brightness over a 0.1738-day period. The spectrum shows aradial velocity variation with the same period, indicating that the surface of the star is regularly pulsating outward and then contracting. This star is rotating rapidly, with a rotational velocity of 199 km/s along theequator.[29]
The secondary member of this system is one of the few stars whose spectrum is affected by the Struve–Sahade effect. This is an anomalous change in the strength of thespectral lines over the course of an orbit, where the lines become weaker as the star is moving away from the observer.[19] It may be caused by a strongstellar wind from the primary scattering the light from secondary when it is receding.[40] This star is smaller than the primary, with about 4 times the mass of the Sun and 3.6 times the Sun's radius.[29] Its stellar classification is B4-7 V, making this amain-sequence star.[6]
Both a rocket and crew capsule designed and under development byCopenhagen Suborbitals, a crowd-funded space program, is named Spica. Spica aims to make Denmark the first country to launch its ownastronaut to space after Russia, the US and China.[41]
^abcDucati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system".CDS/ADC Collection of Electronic Catalogues.2237: 0.Bibcode:2002yCat.2237....0D.
^abRuban, E. V.; Alekseeva, G. A.; Arkharov, A. A.; Hagen-Thorn, E. I.; Galkin, V. D.; Nikanorova, I. N.; Novikov, V. V.; Pakhomov, V. P.; Puzakova, T. Yu. (2006). "Spectrophotometric observations of variable stars".Astronomy Letters.32 (9): 604.Bibcode:2006AstL...32..604R.doi:10.1134/S1063773706090052.S2CID121747360.
^Wilson, Ralph Elmer (1953). "General Catalogue of Stellar Radial Velocities".Carnegie Institute Washington D.C. Publication. Washington: Carnegie Institution of Washington.Bibcode:1953GCRV..C......0W.
^Moesgaard, Kristian P. (1973)."Copernican influence on Tycho Brahe". In Jerzy Dobrzycki (ed.).The reception of Copernicus' heliocentric theory: proceedings of a symposium organized by the Nicolas Copernicus Committee of the International Union of the History and Philosophy of Science. Toruń, Poland: Studia Copernicana, Springer.ISBN90-277-0311-6.
^Johnson, H. L; Morgan, W. W (1953). "Fundamental stellar photometry for standards of spectral type on the Revised System of the Yerkes Spectral Atlas".The Astrophysical Journal.117: 313.Bibcode:1953ApJ...117..313J.doi:10.1086/145697.
^Hoffleit, D.; Warren, W. H., Jr. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised ed. (Hoffleit+, 1991)".Vizier Online Data Catalog.Bibcode:1995yCat.5050....0H.{{cite journal}}: CS1 maint: multiple names: authors list (link)
