Epsilon Boötis (ε Boötis, abbreviated Epsilon Boo, ε Boo), officially named Izar , is a

binary star A binary star 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 using a telescope as separate stars, in wh ...

in the northern

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 origins of the e ...

Boötes Boötes ( ) is a constellation in the northern sky, located between 0° and +60° declination, and 13 and 16 hours of right ascension on the celestial sphere. The name comes from la, Boōtēs, which comes from grc-gre, Βοώτης, Boṓtēs ...

. The star system can be viewed with the unaided eye at night, but resolving the pair with a small telescope is challenging; an

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An opt ...

of or greater is required.

Nomenclature

''ε Boötis'' ( Latinised to ''Epsilon Boötis'') is the star's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...

. It bore the traditional names ''Izar'', ''Mirak'' and ''Mizar'', and was named by

Friedrich Georg Wilhelm von Struve Friedrich Georg Wilhelm von Struve (russian: link=no, Василий Яковлевич Струве, trans. ''Vasily Yakovlevich Struve''; 15 April 1793 – ) was a Baltic German astronomer and geodesist from the famous Struve family. He is bes ...

. ''Izar'', ''Mirak'' and ''Mizar'' are from the ar, إزار, rtl=yes ('veil') and ('the loins'); is

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 of the ...

for 'loveliest'. 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, outreac ...

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 catalogue and standardize proper names for stars. The WGSN approved the name ''Izar'' for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names. In the catalogue of stars in the ''Calendarium of Al Achsasi Al Mouakket'', this star was designated ( ), which was translated into

as , meaning 'belt of barker'. Genghe

Chinese astronomy Astronomy in China has a long history stretching from the Shang dynasty, being refined over a period of more than 3,000 years. The ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categorized in the twe ...

, (' Celestial Lance'), refers to an asterism consisting of Epsilon Boötis, Sigma Boötis and

Rho Boötis Rho Boötis, Latinisation of names, Latinised from ρ Boötis, is a single, orange-hued star in the Northern celestial hemisphere, northern constellation of Boötes. It is visible to the naked eye with an apparent visual magnitude of 3.59. Ba ...

. 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 often a ...

for Epsilon Boötis itself is ('the First Star of Celestial Lance').

Properties

Epsilon Boötis consists of a pair of stars with an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

of at a

position angle In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the north celestial pole (NCP), turning positive into the d ...

of . The brighter component (A) has an

apparent visual 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 lig ...

of 2.37, making it readily visible to the naked eye at night. The fainter component (B) is at magnitude 5.12, which by itself would also be visible to the naked eye.

Parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

measurements from the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

astrometry satellite put the system at a distance of about from the

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 surfa ...

. This means the pair has a

projected separation This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outsid ...

of 185

Astronomical Unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits t ...

s, and they orbit each other with a period of at least 1,000 years. The brighter member 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 grati ...

of K0 II-III, which means it is a fairly late-stage star well into its

stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is cons ...

, having already exhausted its supply of

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

fuel at the core. With more than four times the

mass of the Sun The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

, it has expanded to about 33 times the Sun's radius and is emitting 501 times the

luminosity of the Sun The solar luminosity (), is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

. This energy is being radiated from its outer envelope at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 4,550 K, giving it the orange hue of a

K-type star 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 the ...

. The companion star has a classification of A2 V, so it is a

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

star that is generating energy through the

thermonuclear fusion Thermonuclear fusion is the process of atomic nuclei combining or “fusing” using high temperatures to drive them close enough together for this to become possible. There are two forms of thermonuclear fusion: ''uncontrolled'', in which the re ...

of hydrogen at its core. This star is rotating rapidly, with a projected

rotational velocity In physics, angular velocity or rotational velocity ( or ), also known as angular frequency vector,(UP1) is a pseudovector representation of how fast the angular position or orientation of an object changes with time (i.e. how quickly an objec ...

of . It has a surface temperature of about and a radius nearly three times the Sun, leading to a

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

45 times that of the Sun. By the time the smaller main sequence star reaches the current point of the primary in its evolution, the larger star will have lost much of its mass in a

planetary nebula A planetary nebula (PN, plural PNe) is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to ...

and will have evolved into a

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes fro ...

. The pair will have essentially changed roles: the brighter star becoming the dim dwarf, while the lesser companion will shine as a

giant star A giant star is a star with substantially larger radius and luminosity than a main sequence, main-sequence (or ''dwarf'') star of the same effective temperature, surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moo ...

In culture

In 1973, the Scottish astronomer and science fiction writer

Duncan Lunan Duncan Alasdair Lunan, born October 1945, is a Scottish people, Scottish author with emphasis on astronomy, spaceflight and science fiction, undertaking a wide range of writing and speaking on those and other topics as a researcher, tutor, critic, ...

claimed to have managed to interpret a message caught in the 1920s by two

Norwegian Norwegian, Norwayan, or Norsk may refer to: *Something of, from, or related to Norway, a country in northwestern Europe *Norwegians, both a nation and an ethnic group native to Norway *Demographics of Norway *The Norwegian language, including the ...

physicists that, according to his theory, came from a 13,000 year old satellite polar orbiting the Earth known as the

Black Knight The black knight is a literary stock character who masks his identity and that of his liege by not displaying heraldry. Black knights are usually portrayed as villainous figures who use this anonymity for misdeeds. They are often contrasted with t ...

and sent there by the inhabitants of a planet orbiting Epsilon Boötis. The story was even reported in ''

Time Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to ...

'' magazine. Lunan later withdrew his Epsilon Boötis theory, presenting proofs against it and clarifying why he was brought to formulate it in the first place, but later revoked his withdrawal.

References

External links

Information page for HR 5506 (Izar) on VizieR

Information page for HR 5505 (ε Boötes B) on VizieR

Information page for CCDM J14449+2704 (all component stars) on VizieR

Image of Epsilon Boötis

Izar star chart with viewing information on in-the-sky.org

ε Boötes B star chart with viewing information on in-the-sky.org
{{DEFAULTSORT:Epsilon Bootis Binary stars Bootis, 36 129988 9 072105 Bootis, Epsilon Boötes K-type bright giants K-type giants A-type main-sequence stars

Izar Navantia is a Spanish state-owned shipbuilding company, which offers its services to both military and civil sectors. It is the fifth-largest shipbuilder in Europe and the ninth-largest in the world with shipyards around the globe. The heir to ...

5505 6 BD+27 2417