Mu Sagittarii
Encyclopedia
Mu Sagittarii is a star system
in the constellation
Sagittarius
. It also has the traditional name Polis, from a Coptic
word meaning foal. In ancient Chinese astronomy, it is the 1st of 6 stars in the Dipper
or 'South Dipper' mansion of the Black Tortoise of the North.
The star
s in the Polis system are designated Polis A through Polis E. Polis is more than 3000 light years from Earth
.
The primary component in this system, Polis A, is a type B giant star
with a total luminosity
of 180,000 times that of the Sun
and a radius of 115 times solar. Its mass is 23 times the solar mass
while it has a surface temperature of 11,100 kelvin
s.
Polis A is an eclipsing binary, bringing the total of stars in the system to six. The primary component is a spectral type
B8 supergiant
and the companion is a type B2 giant
. The orbital period
of the binary is 180.55 days. Due to occultation
of the primary by the companion, the apparent magnitude
of Polis A varies between +3.84 and +3.96.
The remaining components are very weakly bound to the Polis system.
Star system
A star system or stellar system is a small number of stars which orbit each other, bound by gravitational attraction. A large number of stars bound by gravitation is generally called a star cluster or galaxy, although, broadly speaking, they are also star systems.-Binary star systems:A stellar...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Sagittarius
Sagittarius (constellation)
Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...
. It also has the traditional name Polis, from a Coptic
Coptic language
Coptic or Coptic Egyptian is the current stage of the Egyptian language, a northern Afro-Asiatic language spoken in Egypt until at least the 17th century. Egyptian began to be written using the Greek alphabet in the 1st century...
word meaning foal. In ancient Chinese astronomy, it is the 1st of 6 stars in the Dipper
Dipper (Chinese constellation)
The 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.
The star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s in the Polis system are designated Polis A through Polis E. Polis is more than 3000 light years from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
.
The primary component in this system, Polis A, is a type B giant star
Giant star
A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same surface temperature. Typically, giant stars have radii between 10 and 100 solar radii and luminosities between 10 and 1,000 times that of the Sun. Stars still more luminous than giants are...
with a total luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
of 180,000 times that of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
and a radius of 115 times solar. Its mass is 23 times the solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
while it has a surface temperature of 11,100 kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
s.
Polis A is an eclipsing binary, bringing the total of stars in the system to six. The primary component is a spectral type
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
B8 supergiant
Supergiant
Supergiants are among the most massive stars. They occupy the top region of the Hertzsprung-Russell diagram. In the Yerkes spectral classification, supergiants are class Ia or Ib . They typically have bolometric absolute magnitudes between -5 and -12...
and the companion is a type B2 giant
Giant star
A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same surface temperature. Typically, giant stars have radii between 10 and 100 solar radii and luminosities between 10 and 1,000 times that of the Sun. Stars still more luminous than giants are...
. The orbital period
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
of the binary is 180.55 days. Due to occultation
Occultation
An 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 . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
of the primary by the companion, the apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of Polis A varies between +3.84 and +3.96.
The remaining components are very weakly bound to the Polis system.
| Component | Apparent Magnitude Apparent magnitude The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere... |
Separation from Polis A |
Minimum distance from Polis A |
|---|---|---|---|
| Polis A | +3.84 | - | - |
| Polis B | +11.5 | 16.9 arcseconds | 42 200 AU or 0.67 ly Light Years Light Years is the seventh studio album by Australian recording artist Kylie Minogue. It was released on 25 September 2000 by Parlophone and Mushroom Records. The album's style was indicative of her return to "mainstream pop dance tunes".... |
| Polis C | +13.5 | 25.8 arcseconds | 64 500 AU or 1.02 ly |
| Polis D | +9.9 | 48.5 arcseconds | 121 200 AU or 1.92 ly |
| Polis E | +9.4 | 50.0 arcseconds | 125 000 AU or 1.98 ly |