Zeta Sagittarii
Encyclopedia
Zeta Sagittarii is the third brightest star system
in the constellation
Sagittarius
. It has the traditional name Ascella from a Late Latin
word meaning armpit.
Ascella is a binary star
, consisting of a spectral class A2 giant
with an apparent magnitude
of +3.26, and an A4 subgiant with apparent magnitude of +3.37. The orbital period
of the binary system is 21 years. The two stars have a mean separation of 13.4 astronomical units (AU)
and the eccentricity of their orbit is 0.205. Ascella has a faint, 10th magnitude companion, Zeta Sagittarii C, separated from the primary by a distance of 75 arcseconds.
Ascella is 90 light years from Earth
. The combined apparent magnitude
of the star system is +2.60.
In ancient Chinese astronomy, it is the 6th star of 6 stars in the Dipper
or 'South Dipper' mansion of the Black Tortoise of the North.
was a United States Navy
Crater class cargo ship
named after the star.
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 has the traditional name Ascella from a Late Latin
Late Latin
Late Latin is the scholarly name for the written Latin of Late Antiquity. The English dictionary definition of Late Latin dates this period from the 3rd to the 6th centuries AD extending in Spain to the 7th. This somewhat ambiguously defined period fits between Classical Latin and Medieval Latin...
word meaning armpit.
Ascella is a binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
, consisting of a spectral class A2 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...
with an 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 +3.26, and an A4 subgiant with apparent magnitude of +3.37. 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 system is 21 years. The two stars have a mean separation of 13.4 astronomical units (AU)
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
and the eccentricity of their orbit is 0.205. Ascella has a faint, 10th magnitude companion, Zeta Sagittarii C, separated from the primary by a distance of 75 arcseconds.
Ascella is 90 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 combined 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 the star system is +2.60.
In ancient Chinese astronomy, it is the 6th star 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.
Namesakes
USS Ascella (AK-137)USS Ascella (AK-137)
USS Ascella was an Crater-class cargo ship commissioned by the U.S. Navy for service in World War II, named after Ascella, a star in the constellation Sagittarius. She was responsible for delivering troops, goods and equipment to locations in the war zone.SS George C. Yount was laid down on 7...
was a United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
Crater class cargo ship
Crater class cargo ship
Crater-class cargo ship is a category of freighter that was constructed for use by the United States Navy during World War II under Maritime Commission EC2-S-C1 type....
named after the star.