Lambda Sagittarii ( Latinized from λ Sagittarii), formally named Kaus Borealis , is a

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

in the southern

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 ...

of Sagittarius. The star marks the top of the Archer's bow.

Properties

With an

apparent visual magnitude Apparent magnitude () is a measure of the 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 of the object's light ca ...

of +2.81, this is one of the brighter members of the constellation and, according to the

Bortle Dark-Sky Scale The Bortle dark-sky scale (usually referred to as simply the Bortle scale) is a nine-level numeric scale that measures the night sky's sky brightness, brightness of a particular location. It quantifies the astronomy, astronomical observability of ...

, it is readily visible to the naked eye. Based upon

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 ...

measurements, it is 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 ...

. Being 2.1 degrees south of 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 ...

, Lambda Sgr is sometimes

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, rarely, by a

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 ...

. The last planet to pass in front of it was

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 ...

, on 19 November 1984. The previous occasion was 5 December 1865, when it was occulted by Mercury. Kaus Borealis is 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 ...

with 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 K1 IIIb. It has a mass 1.8 times that of the

and a physical size of about 11.2 times the

Sun's radius Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: 1\,R_ = 6.957\ti ...

. This expanded outer envelope is radiating energy 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 4,768 K, causing it to glow with the cool 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 ...

. It appears to be rotating at a leisurely rate, with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bu ...

of .

Observation

On 17 December 2021, it had a close conjunction (geocentric separation <1') with Mercury.

Nomenclature

''λ Sagittarii'' ( Latinised to ''Lambda Sagittarii'') is the star's

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 ...

. It bore the traditional name ''Kaus Borealis'', which derives from the

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 ...

قوس ''qaws'' 'bow' and

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 ...

''boreālis'' 'northern'. 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 ''Kaus Borealis'' for this star. This star, with Gamma Sagittarii, Delta Sagittarii, Epsilon Sagittarii, Zeta Sagittarii, Sigma Sagittarii, Tau Sagittarii and Phi Sagittarii comprises the ''

Teapot A teapot is a vessel used for steeping tea leaves or a herbal mix in boiling or near-boiling water and serving the resulting infusion called tea; usually put in a teacup. It is one of the core components of teaware. Teapots usually have an ...

'' asterism. In the catalogue of stars in the ''Calendarium'' of

Al Achsasi al Mouakket Muḥammad al Achsasi al Mouakket () was a 17th century Egyptian astronomer whose and catalogue of stars, ("''Pearls of brilliance upon the solar operations''"), was written in Cairo in about 1650. Al-Achsasi was a shaykh, a learned elder, of th ...

, this star was designated ''Rai al Naaim'', which was translated into

as ''Pastor Struthionum'', meaning ''keeper of the ostriches''. This star is Al Tizini's ''Rāʽi al Naʽāïm'' (ألراع ٱلنعم), the Keeper of the Naʽams (Ostrich), meaning the "keeper" the two asterisms ''al-Naʽām al-Wārid'' ( النعام الوارد ), "The Going Ostriches" and ''al-Naʽām al-Ṣādir'' (النعم الصادر), "The Returning Ostriches". In Chinese, (), meaning ''

Dipper Dippers are members of the genus ''Cinclus'' in the bird family Cinclidae, so-called because of their bobbing or dipping movements. They are unique among passerines for their ability to dive and swim underwater. Taxonomy The genus ''Cinclus'' ...

'', refers to an asterism consisting of Lambda Sagittarii, Phi Sagittarii, Mu Sagittarii, Sigma Sagittarii, Tau Sagittarii and Zeta Sagittarii. Consequently, Lambda Sagittarii itself is (, .)

References

External links

Kaus Borealis
{{DEFAULTSORT:Lambda Sagittarii K-type giants Sagittarius (constellation) Sagittarii, Lambda Durchmusterung objects Sagittarii, 22 090496 169916 6913

Kaus Borealis Lambda Sagittarii (Romanization of Greek, Latinized from λ Sagittarii), formally named Kaus Borealis , is a star in the southern constellation of Sagittarius (constellation), Sagittarius. The star marks the top of the Archer's bow. ...