Lambda Sagittarii (λ Sgr / λ Sagittarii) is a
starA star is a massive, luminous ball of plasma that is held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun...
within the
constellationIn modern astronomy, a constellation is an area of the celestial sphere, defined by exact boundaries.The term "constellation" can also be used loosely to refer to just the more prominent visible stars that seem to form a pattern in that area.-Definitions:...
SagittariusSagittarius is one of the constellations of the zodiac. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...
. The star marks the top of the Archer's bow, whence its traditional name
Kaus Borealis. It also marks the top of the lid of the so-called "Teapot"
asterismIn astronomy, an asterism is a pattern of stars seen in Earth's sky which is not an official constellation. Like constellations, they are composed of stars which, while they are in the same general direction, are not physically related, often being at significantly different distances from Earth....
. In ancient Chinese astronomy, it is the 2nd of 6 stars in the
DipperThe Dipper mansion is one of the Twenty-eight mansions of the Chinese constellations. It is one of the northern mansions of the Black Tortoise.- Asterisms :- Stars :* ζ Sgr* τ Sgr* σ Sgr* φ Sgr* λ Sgr* μ Sgr...
or 'South Dipper' mansion of the Black Tortoise of the North.
Kaus Borealis is a
spectral classIn astronomy, stellar classification is a classification of stars based on its spectral characteristics. The spectral class of a star, is a designation of a class to a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective...
K orange giant star. It is currently fusing
heliumHelium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...
into
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
and
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
in its core. Kaus Borealis is 77 light years from us, with a mass 2.3 times that of the
SunThe solar mass , , is a standard way to express mass in astronomy, used to describe the masses of other stars and galaxies. It is equal to the mass of the Sun, about two nonillion kilograms or about 332,950 times the mass of the Earth or 1,048 times the mass of Jupiter.The solar mass can be...
It is 52 times more luminous than the
SunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
and has a radius of some 11 Suns.
Being near the
eclipticThe ecliptic is the apparent path that the Sun traces out in the sky during the year, appearing to move eastwards on an imaginary spherical surface, the celestial sphere, relative to the fixed stars. More accurately, it is the intersection of the celestial sphere with the ecliptic plane, which is...
, Lambda Sgr is sometimes
occultedAn occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy and can also be used in a general sense to describe when an object in the foreground occults objects in the background...
by the
MoonThe Moon is Earth's only natural satellite and the fifth largest satellite in the Solar System. The average centre-to-centre distance from the Earth to the Moon is , about thirty times the diameter of the Earth. The common centre of mass of the system is located at about —a quarter the Earth's...
and , more rarely by a
planetA planet , is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
. The last planet to pass in front of it was
VenusVenus is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6...
, on 19 November 1984. The previous occasion was on 5 December 1865, when it was occulted by the planet
MercuryFor the liquid metallic element, see Mercury .Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three...
.
Etymology
The name Kaus Australis comes from the
ArabicArabic is a Central Semitic language, thus related to and classified alongside other Semitic languages such as Hebrew and the Neo-Aramaic languages. In terms of speakers, the Arabic macrolanguage is the largest member of the Semitic language family. It is spoken by more than 280 million people as...
قوس
qaws 'bow' and
LatinLatin is an Italic language originally spoken in Latium and Ancient Rome. Through the Roman conquest, Latin spread throughout the Mediterranean and a large part of Europe...
boreālis 'northern'. To the south of it lie the other stars of the bow, Kaus Media and Kaus Australis.