Spica is the brightest object in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Virgo Virgo may refer to: Arts and entertainment * Virgo (film), a 1970 Egyptian film * Virgo (character), several Marvel Comics characters * Virgo Asmita, a character in the manga ''Saint Seiya: The Lost Canvas'' * ''Virgo'' (album), by Virgo Four, ...

and one of the 20 brightest 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 include moonlig ...

. It has the

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

α Virginis, which is Latinised to Alpha Virginis and abbreviated Alpha Vir or α Vir. Analysis of its

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

shows that it is located 250

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s from the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

. It is a spectroscopic

binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

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 systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

of the Beta Cephei type. Spica, along with

Arcturus , - bgcolor="#FFFAFA" , Note (category: variability): , , H and K emission vary. Arcturus is a red giant star in the Northern celestial hemisphere, northern constellation of Boötes, and the brightest star in the constellation. It ha ...

and Denebola—or

Regulus Regulus is the brightest object in the constellation Leo (constellation), Leo and one of the List of brightest stars, brightest stars in the night sky. It has the Bayer designation designated α Leonis, which is Latinisation of names, ...

, depending on the source—forms the

Spring Triangle The Spring Triangle is an asterism_(astronomy), astronomical asterism involving an imaginary triangle drawn upon the celestial sphere, with its defining vertices at Arcturus, Spica, and Regulus. This triangle connects the constellations of Boötes ...

asterism, and, by extension, is also part of the Great Diamond together with the star Cor Caroli.

Nomenclature

In 2016, the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

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 proper names for stars for the international astronomical community. It operates under Division C – Education ...

(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 languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

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

heat In thermodynamics, heat is energy in transfer between a thermodynamic system and its surroundings by such mechanisms as thermal conduction, electromagnetic radiation, and friction, which are microscopic in nature, involving sub-atomic, ato ...

grain". It was also anglicized as ''Virgin's Spike''. ''α Virginis'' ( Latinised to ''Alpha Virginis'') is the system's

Johann Bayer Johann Bayer (; 1572 – 7 March 1625) was a German lawyer and uranographer (celestial cartographer). He was born in Rain in 1572. In 1592, aged 20, he began his study of philosophy and law at the University of Ingolstadt, after which he ...

cited the name ''Arista''. Other traditional names are ''Azimech'' , from

Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...

السماك الأعزل ''al-simāk al-ʼaʽzal'' 'the unarmed ''simāk'' (of unknown meaning, cf. Eta Boötis); ''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 Horn may refer to: Common uses * Horn (acoustic), a tapered sound guide ** Horn antenna ** Horn loudspeaker ** Vehicle horn ** Train horn *Horn (anatomy), a pointed, bony projection on the head of various animals * Horn (instrument), a family ...

(asterism)'', refers to an asterism consisting of Spica and ζ Virginis. Consequently, the

Chinese name Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethni ...

for Spica is (, ). In

Hindu astronomy Astronomy has a long history in the Indian subcontinent, stretching from pre-historic to modern times. Some of the earliest roots of Indian astronomy can be dated to the period of Indus Valley civilisation or earlier. Astronomy later develope ...

, Spica corresponds to the

Nakshatra Nakshatra () is the term for Lunar mansion in Hindu astrology and Buddhist astrology. A nakshatra is one of 27 (sometimes also 28) sectors along the ecliptic. Their names are related to a prominent star or asterisms in or near the respective s ...

''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 (; , ; BC) was a Ancient Greek astronomy, 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 equinoxes. Hippar ...

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 Rotation around a fixed axis, rotational axis. In the absence of precession, the astronomical body's orbit would show ...

. A

temple A temple (from the Latin ) is a place of worship, a building used for spiritual rituals and activities such as prayer and sacrifice. By convention, the specially built places of worship of some religions are commonly called "temples" in Engli ...

Menat In ancient Egyptian religion, a menat (, ) was a necklace closely associated with the goddess Hathor. Operation The menat was held in the hand by its counterpoise and used as a Rattle (percussion instrument), rattle by Hathor's priestesses. It ...

(an early

Hathor Hathor (, , , Meroitic language, Meroitic: ') was a major ancient Egyptian deities, 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 god Horus and the sun god R ...

) 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 (19 February 1473 – 24 May 1543) was a Renaissance polymath who formulated a mathematical model, model of Celestial spheres#Renaissance, the universe that placed heliocentrism, the Sun rather than Earth at its cen ...

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 Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

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 f ...

by the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

and sometimes by

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

s. The last planetary occultation of Spica occurred when

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

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 Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

) 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 The heliacal rising ( ) of a star or a planet occurs annually when it becomes visible above the eastern horizon at dawn just before sunrise (thus becoming "the Morning Star (disambiguation)#Astronomy, morning star"). A heliacal rising marks the ti ...

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 (American English, US, Canadian English, Canada) or the Plough (British English, UK, Hiberno-English, Ireland) is an asterism (astronomy), asterism consisting of seven bright stars of the constellation Ursa Major; six of them ar ...

(or Plough) to Arcturus, and then continue on the same

angular distance Angular distance or angular separation is the measure of the angle between the orientation (geometry), orientation of two straight lines, ray (geometry), rays, or vector (geometry), vectors in three-dimensional space, or the central angle subtende ...

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 A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets below the horizon due to its apparent proximity to one of the celestial poles. Circumpolar stars are therefore visible from said location toward the nearest p ...

for the viewer) culminate at midnight—noticeable where viewed away from any polar region experiencing

midnight sun Midnight sun, also known as polar day, 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 midnight sun is see ...

—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 In astronomy, an epoch or reference epoch is a moment in time used as a reference point for some time-varying astronomical quantity. It is useful for the celestial coordinates or orbital elements of a celestial body, as they are subject to pert ...

Physical properties

Spica is a close

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 (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...

. The changes in the orbital motion of this pair results in a

Doppler shift The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described t ...

in the

absorption line Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption (electromagnetic radiation), absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. Th ...

s 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 In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the longe ...

of the orbit was found to be only slightly larger at . 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 Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

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. AlphaVirLightCurve

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 In astronomy, the geometric albedo of a celestial body is the ratio of its actual brightness as seen from the light source (i.e. at zero phase angle (astronomy), phase angle) to that of an ''idealized'' flat, fully reflecting, diffuse reflection, d ...

) 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 ''Spectral'' is a 2016 Hungarian-American military science fiction action film co-written and directed by Nic Mathieu. Written with Ian Fried & George Nolfi, the film stars James Badge Dale as DARPA research scientist Mark Clyne, with Max M ...

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 The Bright Star Catalogue, also known as the Yale Catalogue of Bright Stars, Yale Bright Star Catalogue, or just YBS, is a star catalogue that lists all stars of stellar magnitude 6.5 or brighter, which is roughly every star visible to the na ...

listed a spectral class of B1III-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 stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

of B1III-IV. The

luminosity class In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

matches the spectrum of a star that is midway between a

subgiant A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...

and a

giant star A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsp ...

, and it is no longer a

main-sequence star In astronomy, the main sequence is a classification of stars which appear on plots of stellar color versus brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or dwarf stars, and positions of 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 The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies a ...

and seven times its radius. The

bolometric luminosity Luminosity is an absolute measure of radiated electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electromagnetic energy emitted per ...

of the primary is about 20,500 times that of the

, 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 A Type II supernova or SNII (plural: ''supernovae'') results from the rapid collapse and violent explosion of a massive star. A star must have at least eight times, but no more than 40 to 50 times, the mass of the Sun () to undergo this type ...

explosion. 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 a

Beta Cephei Beta Cephei (β Cephei, abbreviated Beta Cep, β Cep) is a triple star system of the third magnitude in the constellation of Cepheus. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 690 light-y ...

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

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative 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 the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

. 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 weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission (electromagnetic radiation), emission or absorption (electromagnetic radiation), absorption of light in a narrow frequency ...

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 A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...

from the primary scattering the light from secondary when it is receding. This star is smaller than the primary, with about 4 times the mass of the Sun and 3.6 times the Sun's radius. Its stellar classification is B4-7 V, making this a

In culture

Both a rocket and crew capsule designed and under development by

Copenhagen Suborbitals Copenhagen Suborbitals is a crowd-funded human space program. It has flown six home-built rockets and capsules since 2011. The organization successfully launched its Nexø II rocket in the summer of 2018. Its stated goal is to have one of its me ...

, 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 List of human spaceflight programs, human spaceflight program to serve as a commander or crew member of a spa ...

to space after Russia, the US and China. Spica is one of the Behenian fixed stars. In his ''

Three Books of Occult Philosophy ''Three Books of Occult Philosophy'' (''De Occulta Philosophia libri III'') is Heinrich Cornelius Agrippa's study of occult philosophy, acknowledged as a significant contribution to the Renaissance philosophical discussion concerning the powe ...

'', Cornelius Agrippa attributes Spica's

kabbalistic Kabbalah or Qabalah ( ; , ; ) is an esoteric method, discipline and school of thought in Jewish mysticism. It forms the foundation of mystical religious interpretations within Judaism. A traditional Kabbalist is called a Mekubbal (). Jewi ...

symbol to

Hermes Trismegistus Hermes Trismegistus (from , "Hermes the Thrice-Greatest") is a legendary Hellenistic period figure that originated as a syncretic combination of the Greek god Hermes and the Egyptian god Thoth.A survey of the literary and archaeological eviden ...

References