Zeta Sagittarii (ζ Sagittarii, abbreviated Zeta Sgr, ζ Sgr) is a triple

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speak ...

and the third-brightest

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

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 origins of the e ...

of Sagittarius. Based upon

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, it is about from the Sun. The three components are designated Zeta Sagittarii A (officially named Ascella , the traditional name for the entire system) and B, themselves forming a binary pair, and a smaller companion star, C.

Nomenclature

''ζ Sagittarii'' ( Latinised to ''Zeta Sagittarii'') is the system'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. ...

. The designations of the two components as ''ζ Sagittarii A'', ''B'' and ''C'' derive from the convention used by the Washington Multiplicity Catalog (WMC) for

multiple star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speaki ...

s, and adopted by the International Astronomical Union (IAU). It bore the traditional name ''Ascella'', from a Late Latin word meaning ''armpit''. In the catalogue of stars in the ''Calendarium'' of Al Achsasi al Mouakket, this star was designated ''Thalath al Sadirah'', which was translated into Latin as ''Tertia τού al Sadirah'', meaning ''third returning ostrich''. In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name ''Ascella'' for the component Zeta Sagittarii A on 12 September 2016 and it is now so included in the List of IAU-approved Star Names. This star, together with

Gamma Sagittarii The Bayer designation γ Sagittarii (Gamma Sagittarii) is shared by two stars 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, ...

, Delta Sagittarii, Epsilon Sagittarii, Lambda Sagittarii,

Sigma Sagittarii Sigma Sagittarii, Latinized from σ Sagittarii; formally named Nunki , is the second-brightest star in the constellation of Sagittarius. It has an apparent magnitude of +2.05, making it readily visible to the naked eye. The distanc ...

, Tau Sagittarii and

Phi Sagittarii Phi Sagittarii, Latinized from φ Sagittarii, is a star in the southern constellation of Sagittarius. With an apparent visual magnitude of 3.17, it is the ninth-brightest star in the constellation and is readily visible to the nak ...

comprise the '' Teapot'' asterism. In Chinese, (), meaning '' Dipper'', refers to an asterism consisting of Zeta Sagittarii, Phi Sagittarii, Lambda Sagittarii, Mu Sagittarii, Sigma Sagittarii and Tau Sagittarii. Consequently, the Chinese name for Zeta Sagittarii itself is (, en, the First Star of Dipper).AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日
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Properties

Zeta Sagittarii has a combined apparent visual magnitude of +2.59. It is moving away from the Solar System with 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 temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

of 22 km s⁻¹, and some 1.0–1.4 million years ago, came within of the Sun. The two components Zeta Sagittarii A and B orbit each other over a period of 21 years at an eccentricity of 0.211. The combined mass of the binary pair is 5.26 ± 0.37 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 ...

and their blended

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 ...

is A2.5 Va. A is a spectral class A2 giant with an apparent magnitude of +3.27, and B is an A4 subgiant with apparent magnitude of +3.48. The pair have a mean separation of 13.4 AU. The binary pair have a faint, 10th-magnitude companion, C, separated from them by a distance of 75

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

s. Zeta Sagittarii was the brightest star in the night sky around 1.2 million years ago, – based on computations from

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 ...

data. (The calculations exclude stars whose distance or

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

is uncertain.) tp://tlgleonid.asuscomm.com/HITACHI/BOOK_ASTRO/S&T/SkyandTelescope_1998%20-%20astronomy/04/199804059063.pdf PDF/ref> peaking with an apparent magnitude of -2.74.

References

{{DEFAULTSORT:Zeta Sagittarii Sagittarii, Zeta Sagittarius (constellation) Binary stars A-type giants A-type subgiants

Ascella Zeta Sagittarii (ζ Sagittarii, abbreviated Zeta Sgr, ζ Sgr) is a triple star system and the third-brightest star in the constellation of Sagittarius. Based upon parallax measurements, it is about from the Sun. The thr ...

Sagittarii, 38 093506 7194 176687 Durchmusterung objects A-type main-sequence stars