Gamma Crucis
Encyclopedia
Gamma Crucis often called Gacrux, is a red giant
star
approximately 88 light-year
s away in the constellation
of Crux
. Among Portuguese-speaking peoples it is also named "Rubídea" (or Ruby-like), in reference to its color. The star is the third-brightest star in Crux (the Southern Cross) and one of the brightest stars in the night sky. A line from the two "Pointers", Alpha Centauri
through Beta Centauri
, leads to within a few degrees of this star.
, 88 light years distant from Earth. The main star is of apparent magnitude
+1.6 and spectral classification M4 III. Its +6.4 magnitude white companion star (spectral classification A3) lies about 2 arcminutes away at an angle of 128 degrees from the main star, and can be observed with binoculars
. But it is only an optical companion, which is about 400 light years distant from Earth. The colour of Gamma Crucis A is a prominent reddish-orange, well in keeping with its spectral classification.
Gacrux has evolved off of the main sequence
to become a red giant
star, and may even be evolving past the helium
-burning stage. It is also semi-variable with a period of about 90 days. The atmosphere is enriched with barium
, which is likely due to neutron emission from an undetected white dwarf
companion.
, it is only visible south of the Tropic of Cancer
and so lacks an ancient name.
In Chinese
, , meaning Cross, refers to an asterism consisting of γ Crucis, α Crucis
, β Crucis
and δ Crucis. Consequently, γ Crucis itself is known as .
The people of Aranda
and Luritja
tribe around Hermannsburg
, Central Australia
named Iritjinga, "The Eagle-hawk", a quadrangular arrangement comprising this star, δ Cru (Palida), γ Cen
(Muhilfain) and δ Cen
(Ma Wei).
, New Zealand
and Papua New Guinea
as one of five stars which comprise the Southern Cross. It is also featured in the flag of Brazil
, along with 26 other stars, each of which represents a state. γ Cru represents the State of Bahia
.
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
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...
approximately 88 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away 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....
of Crux
Crux
Crux is the smallest of the 88 modern constellations, but is one of the most distinctive. Its name is Latin for cross, and it is dominated by a cross-shaped asterism that is commonly known as the Southern Cross.-Visibility:...
. Among Portuguese-speaking peoples it is also named "Rubídea" (or Ruby-like), in reference to its color. The star is the third-brightest star in Crux (the Southern Cross) and one of the brightest stars in the night sky. A line from the two "Pointers", Alpha Centauri
Alpha Centauri
Alpha Centauri is the brightest star in the southern constellation of Centaurus...
through Beta Centauri
Beta Centauri
Beta Centauri , also known as Hadar or Agena, is the second brightest star in the constellation Centaurus and the tenth brightest star in the night sky. Beta Centauri is a B1 III blue-white giant star that the astrometric Hipparcos satellite calculates as about 161 parsecs or 525 light-years from...
, leads to within a few degrees of this star.
Physical properties
Gamma Crucis is a double starDouble star
In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary star, i.e...
, 88 light years distant from Earth. The main star is of 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...
+1.6 and spectral classification M4 III. Its +6.4 magnitude white companion star (spectral classification A3) lies about 2 arcminutes away at an angle of 128 degrees from the main star, and can be observed with binoculars
Binoculars
Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
. But it is only an optical companion, which is about 400 light years distant from Earth. The colour of Gamma Crucis A is a prominent reddish-orange, well in keeping with its spectral classification.
Gacrux has evolved off of the main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
to become a red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
star, and may even be evolving past the helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which 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...
-burning stage. It is also semi-variable with a period of about 90 days. The atmosphere is enriched with barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
, which is likely due to neutron emission from an undetected white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
companion.
Etymology
Since Gamma Crucis, "Gacrux", is at roughly −60° declinationDeclination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
, it is only visible south of the Tropic of Cancer
Tropic of Cancer
The Tropic of Cancer, also referred to as the Northern tropic, is the circle of latitude on the Earth that marks the most northerly position at which the Sun may appear directly overhead at its zenith...
and so lacks an ancient name.
In Chinese
Chinese language
The Chinese language is a language or language family consisting of varieties which are mutually intelligible to varying degrees. Originally the indigenous languages spoken by the Han Chinese in China, it forms one of the branches of Sino-Tibetan family of languages...
, , meaning Cross, refers to an asterism consisting of γ Crucis, α Crucis
Alpha Crucis
Acrux is the brightest star in the constellation Crux, the Southern Cross, and, at a combined visual magnitude 0.77, is the twelfth brightest star in the night sky...
, β Crucis
Beta Crucis
Mimosa or Becrux is the second brightest star in the constellation Crux and is one of the brightest stars in the night sky....
and δ Crucis. Consequently, γ Crucis itself is known as .
The people of Aranda
Aranda
-Places and events:*Aranda de Duero, a Spanish town located in Burgos province, the site of the Council of Aranda*Aranda , see Comarcas of Aragon*Aranda, Australian Capital Territory, a Canberra suburb named after the Arrernte people...
and Luritja
Luritja
Luritja is a name used to refer to several dialects of the Indigenous Australian Western Desert Language, and thereby also to the people who speak these varieties, and their traditional lands.-Origin and meaning of Luritja:...
tribe around Hermannsburg
Hermannsburg
Hermannsburg is a municipality in the Celle district, in Lower Saxony, Germany. It is situated at the River Örtze, approx. 15 kilometers east of Bergen and 30 kilometers north of Celle.-Division of the municipality:...
, Central Australia
Central Australia
Central Australia/Alice Springs Region is one of the five regions in the Northern Territory. The term Central Australia is used to describe an area centred on Alice Springs in Australia. It is sometimes referred to as Centralia; likewise the people of the area are sometimes called Centralians...
named Iritjinga, "The Eagle-hawk", a quadrangular arrangement comprising this star, δ Cru (Palida), γ Cen
Gamma Centauri
Gamma Centauri is a star in the constellation Centaurus. It has the proper name Muhlifain, not to be confused with Muliphein, which is γ Canis Majoris; both names derive from the same Arabic root....
(Muhilfain) and δ Cen
Delta Centauri
Delta Centauri is a star in the constellation Centaurus.It is the B type third-magnitude star. It is classified as a Gamma Cassiopeiae type variable star and its brightness varies from magnitude +2.51 to +2.65....
(Ma Wei).
Modern legacy
γ Cru is represented in the flags of AustraliaFlag of Australia
The flag of Australia is a defaced Blue Ensign: a blue field with the Union Flag in the canton , and a large white seven-pointed star known as the Commonwealth Star in the lower hoist quarter...
, New Zealand
Flag of New Zealand
The flag of New Zealand is a defaced Blue Ensign with the Union Flag in the canton, and four red stars with white borders to the right. The stars represent the constellation of Crux, the Southern Cross....
and Papua New Guinea
Flag of Papua New Guinea
The flag of Papua New Guinea was adopted on July 1, 1971. In the hoist, it depicts the Southern Cross; in the fly, a raggiana bird of paradise is silhouetted. The designer of the flag was 15 year old schoolgirl Susan Huhume who won a nationwide competition for a new flag design in 1971.Red and...
as one of five stars which comprise the Southern Cross. It is also featured in the flag of Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, along with 26 other stars, each of which represents a state. γ Cru represents the State of Bahia
Bahia
Bahia is one of the 26 states of Brazil, and is located in the northeastern part of the country on the Atlantic coast. It is the fourth most populous Brazilian state after São Paulo, Minas Gerais and Rio de Janeiro, and the fifth-largest in size...
.