Spica is the brightest object in the constellation of Virgo and one of the 20

brightest stars This is a list of stars arranged by their apparent magnitude – their brightness as observed from Earth. It includes all stars brighter than magnitude +2.50 in visible light, measured using a ''V''-band filter in the UBV photometric system. Stars ...

in the

night sky The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon. Natural light sources in a night sky inc ...

. It has the Bayer designation α Virginis, which is Latinised to Alpha Virginis and abbreviated Alpha Vir or α Vir. Analysis of its parallax shows that it is located 250

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 101 ...

s from the Sun. It is a

spectroscopic Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter ...

binary star and rotating ellipsoidal variable; a system whose two stars are so close together they are egg-shaped rather than spherical, and can only be separated by their spectra. The primary is a blue giant and a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

of the Beta Cephei type. Spica, along with Arcturus and Denebola—or Regulus, depending on the source—forms the Spring Triangle asterism, and, by extension, is also part of the

Great Diamond The Great Diamond is an asterism. Astronomy popularizer Hans A. Rey called it the Virgin's Diamond. (In fact, long before mentioned in R. Hinckley-Allen's "Star-Names and Their Meanings", 1899, p.259, as "the celebrated Diamond of Virgo"; see ...

together with the star Cor Caroli.

Nomenclature

In 2016, the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize List of proper names of stars, proper names for stars for the international astronomical community. It operates under ...

(WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included ''Spica'' for this star. It is now so entered in the IAU Catalog of Star Names. The name is derived from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power ...

''spīca virginis'' "the virgin's ear of

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

grain". It was also anglicized as ''Virgin's Spike''. ''α Virginis'' ( Latinised to ''Alpha Virginis'') is the system's Bayer designation. Johann Bayer cited the name ''Arista''. Other traditional names are ''Azimech'' , from

Arabic Arabic (, ' ; , ' or ) is a Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C. E.Watson; Walte ...

السماك الأعزل ''al-simāk al-ʼaʽzal'' 'the unarmed ''simāk'' (of unknown meaning, cf.

Eta Boötis Eta Boötis (η Boötis, abbreviated Eta Boo, η Boo) is a binary star in the constellation of Boötes. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 37 light-years (11 parsecs) distant from th ...

); ''Alarph'', Arabic for 'the grape-gatherer' or 'gleaner', and ''Sumbalet'' (''Sombalet'', ''Sembalet'' and variants), from Arabic سنبلة ''sunbulah'' "ear of grain". In Chinese, (), meaning '' Horn (asterism)'', refers to an asterism consisting of Spica and

ζ Virginis Zeta Virginis (ζ Virginis, abbreviated Zeta Vir, ζ Vir) is a binary star in the zodiac constellation of Virgo. It is visible to the naked eye with an apparent visual magnitude of +3.376 and is located about a half degree south of the ...

. Consequently, the

Chinese name Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are oft ...

for Spica is (, en, the First Star of Horn). In Hindu astronomy, Spica corresponds to the

Nakshatra Nakshatra ( sa, नक्षत्रम्, translit=Nakṣatram) is the term for lunar mansion in Hindu astrology and Indian Astronomy. A nakshatra is one of 27 (sometimes also 28) sectors along the ecliptic. Their names are related to ...

''Chitrā''.

Observational history

As one of the nearest massive binary star systems to the Sun, Spica has been the subject of many observational studies. Spica is believed to be the star that gave

Hipparchus Hipparchus (; el, Ἵππαρχος, ''Hipparkhos''; BC) was a Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry, but is most famous for his incidental discovery of the precession of the equ ...

the data that led him to discover the

precession of the equinoxes In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In particu ...

. A

temple A temple (from the Latin ) is a building reserved for spiritual rituals and activities such as prayer and sacrifice. Religions which erect temples include Christianity (whose temples are typically called church (building), churches), Hindui ...

to Menat (an early

Hathor Hathor ( egy, ḥwt-ḥr, lit=House of Horus, grc, Ἁθώρ , cop, ϩⲁⲑⲱⲣ, Meroitic: ) was a major goddess in ancient Egyptian religion who played a wide variety of roles. As a sky deity, she was the mother or consort of the sky ...

) at Thebes 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.

Nicolaus Copernicus Nicolaus Copernicus (; pl, Mikołaj Kopernik; gml, Niklas Koppernigk, german: Nikolaus Kopernikus; 19 February 1473 – 24 May 1543) was a Renaissance polymath, active as a mathematician, astronomer, and Catholic canon, who formulat ...

made many observations of Spica with his home-made triquetrum for his researches on precession.

Observation

Spica is 2.06 degrees from the

ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agai ...

and can be

occulted An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...

by the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width ...

and sometimes by

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a ...

s. The last planetary occultation of Spica occurred when

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...

passed in front of the star (as seen from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...

) on November 10, 1783. The next occultation will occur on September 2, 2197, when Venus again passes in front of Spica. The Sun passes a little more than 2° north of Spica around October 16 every year, and the star's heliacal 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. A method of finding Spica is to follow the arc of the handle of the

Big Dipper The Big Dipper ( US, Canada) or the Plough ( UK, Ireland) is a large asterism consisting of seven bright stars of the constellation Ursa Major; six of them are of second magnitude and one, Megrez (δ), of third magnitude. Four define a "bowl ...

(or Plough) to Arcturus, and then continue on the same angular distance to Spica. This can be recalled by the mnemonic phrase, "arc to Arcturus and spike to Spica." Stars that can set (not in a circumpolar constellation for the viewer) culminate at midnight—noticeable where viewed away from any polar region experiencing

midnight sun The midnight sun is a natural phenomenon that occurs in the summer months in places north of the Arctic Circle or south of the Antarctic Circle, when the Sun remains visible at the local midnight. When the midnight sun is seen in the Arctic, ...

—when at opposition, meaning they can be viewed from dusk until dawn. This applies to α Virginis on 12 April, in the current astronomical epoch.

Physical properties

Spica is a close binary star whose components orbit each other every four days. They stay close enough together that they cannot be resolved as two stars through a

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...

. The changes in the orbital motion of this pair results in a Doppler shift in the absorption lines of their respective spectra, making them a double-lined spectroscopic binary. Initially, the orbital parameters for this system were inferred using spectroscopic measurements. Between 1966 and 1970, the Narrabri 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 , and the angular size of the semi-major axis of the orbit was found to be only slightly larger at . AlphaVirLightCurve

Spica is a rotating ellipsoidal variable, which is a non-eclipsing close binary star system where the stars are mutually distorted through their gravitational interaction. This effect causes the

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

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. 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 and orbit circularization. Spica is a polarimetric variable, first discovered to be such in 2016. 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 (or geometric albedo) measured. The geometric albedos of Spica A and B are, respectively, 3.61 percent and 1.36 percent, values that are low compared to planets. The MK spectral classification of Spica is typically considered to be an early B-type main-sequence star. Individual spectral types for the two components are difficult to assign accurately, especially for the secondary due to the Struve–Sahade effect. The Bright Star Catalogue derived a spectral class of B1 III-IV for the primary and B2V for the secondary, but later studies have given various different values. The primary star has a

stellar classification In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting t ...

of B1 III–IV. The luminosity class matches the spectrum of a star that is midway between a subgiant and a

giant star A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...

, and it is no longer a main-sequence star. The evolutionary stage has been calculated to be near or slightly past the end of the main-sequence phase. This is a massive star with more than 10 times the mass of the Sun and seven times its radius. The bolometric luminosity of the primary is about 20,500 times that of the Sun, and nine times the luminosity of its companion. The primary is one of the nearest stars to the Sun that has enough mass to end its life in a Type II supernova explosion. However, since Spica has recently left the main sequence, this event is not likely to occur for several more million years. The primary is classified as a Beta Cephei

that varies in brightness over a 0.1738-day period. The spectrum shows a

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...

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 the

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can al ...

. 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 the

spectral line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

s over the course of an orbit, where the lines become weaker as the star is moving away from the observer. It may be caused by a strong stellar wind from the primary scattering the light from secondary when it is receding. This star is smaller than the primary, with about 7 times the mass of the Sun and 3.6 times the Sun's radius. Its stellar classification is B2 V, making this a main-sequence star.

In culture

Both American ships USS ''Spica'' (AK-16) and USNS ''Spica'' (T-AFS-9) were named after this star while USS ''Azimech'' (AK-124), a ''Crater''-class cargo ship, was given one of the star's medieval names. Both a rocket and crew capsule designed and under development by Copenhagen Suborbitals, a crowd-funded space program, is named Spica. Spica aims to make Denmark the first country to launch its own

astronaut An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally r ...

to space after Russia, the US and China. A blue star represents Spica on the

flag A flag is a piece of fabric (most often rectangular or quadrilateral) with a distinctive design and colours. It is used as a symbol, a signalling device, or for decoration. The term ''flag'' is also used to refer to the graphic design emp ...

of the Brazilian state of Pará. Spica is also the star representing Pará on the Brazilian flag. In his '' Three Books of Occult Philosophy'', Cornelius Agrippa attributes Spica's

Kabbalistic Kabbalah ( he, קַבָּלָה ''Qabbālā'', literally "reception, tradition") is an esoteric method, discipline and school of thought in Jewish mysticism. A traditional Kabbalist is called a Mekubbal ( ''Məqūbbāl'' "receiver"). The defin ...

symbol to

Hermes Trismegistus Hermes Trismegistus (from grc, Ἑρμῆς ὁ Τρισμέγιστος, "Hermes the Thrice-Greatest"; Classical Latin: la, label=none, Mercurius ter Maximus) is a legendary Hellenistic figure that originated as a syncretic combination of t ...

References