What is the Southern Cross constellation?
The South Cross (Crux or Crux Australis), in contrast to the Northern Cross, is the smallest of the 88 modern constellations, but also one of the most famous. It is located touching the constellation Centaurus, while to its south we find Musca.
Southern Cross: Main Stars
Acrux (α Raw)
Acrux (α Raw) is the brightest star in the constellation. With an apparent magnitude of 0.77, it is the 22nd star in luminosity, and the southernmost first magnitude star.
Acrux It is a binary star, made up of two hot blue supergiants, α 1 Crude (magnitude 1.4) and α 2 Crude (magnitude 1.9). Distant 320 light years), they are 25,000 and 16,000 times brighter than the Sun and circle each other in 1,500 years, separated by 420 AU.
α 1 Crudo is a double star, but the two stars that form it are inseparable by the telescope. They are only known to orbit in 76 days, a little less than one AU (astronomical unit) away.
A last comet seems to accompany the other three, but perhaps this is an optical effect and its distance from Earth is difficult to calculate, since it is very dim.
Acrux It is a little too far south to receive a name from the astronomers of ancient Mediterranean times. Consequently, its name is the juxtaposition of the first letter of the alphabet with the Latin name of the constellation.
Mimosa (β Crucis)
Mimosa (Crude β), of magnitude 1.25, is a blue giant that radiates mainly in the ultraviolet. It is a variable star of the Beta Cephei class, which varies from magnitude 1.23 to 1.31, according to multiple periods, the shortest being 5.68 days.
Mimosa It is probably a double star. The two stars orbit each other in about 5 years and cannot be separated by telescope.
Like Acrux, Mimosa (sometimes called Becrux following the same scheme) did not have its own name in ancient times. Its current name, therefore, is recent but its origin is unknown.
Gacrux (γ Crucis)
Gacrux (γ Crude) -of magnitude 1.59- is a red giant, 113 times larger than the Sun; It is the 24th brightest star in the sky. It is slightly variable, irregular in character and, perhaps, has a companion, since its barium-enriched spectrum shows possible contamination by another star. Its name has been built according to the same logic as Acrux.
δ Crude (of magnitude 2.79) and ε Crude (magnitude 3.59) are the other two brightest stars in this constellation.
Notable features of the Southern Cross constellation
With the lack of a major pole star in the southern hemisphere (δ Octantis is close to the pole, but is too faint to be used to mark it), two stars of Crux (Alpha and Gamma) are used to mark south. Following the line thus defined by two stars, approximately 4.5 times the distance between them, we arrive very close to the south celestial pole.
If a line is constructed perpendicular to the segment defined by α Centauri and β Centauri, the point of intersection with the line mentioned above marks the south celestial pole.
As there is nothing opposite to Ursa Major, in tropical regions both the Southern Cross and Ursa Major (low in the north) can be seen during April-June. It is opposite Cassiopeia in the sky and therefore cannot be seen at the same time. In places located further south than 34° latitude, it is always completely visible in the sky.
Notable Deep Sky Objects of the Southern Cross
The Coalsack nebula It is the most prominent absorption nebula in the heavens, clearly visible to the naked eye as a black trail in the southern Milky Way.
Another deep sky object in the Southern Cross is the open cluster NGC 4755also know as Kappa Crucis cluster, discovered by Nicolas Louis de Lacaille in 1751-1752. This cluster is about 7,500 light years away, with about 100 stars spanning about 20 light years.
History of the Southern Cross constellation
Due to the precession of the equinox, Crux It was visible from the Mediterranean area in ancient times; Therefore, these stars were known to Greek astronomers. Be that as it may, these stars were not considered a constellation, but rather a part of Centaurus.
The creation of Crux as a separate constellation is generally attributed to the French astronomer Augustin Royer, in 1679.
Flags with the Southern Cross constellation
The five brightest stars of Crux (α, β, γ, δ and ε Crucis) are shown on the flags of Australia, Brazil, New Zealand, Papua, New Guinea and Samoa, and the Australian states and territories of Victoria, the territory of the capital of Australia, the Northern Territory of Australia and also the flag of the Magallanes region of Chile and the province of Tierra del Fuego, Antarctica and the South Atlantic Islands, in Argentina. The Mercosur flag features the four stars. Crux It also appears on the coat of arms of Brazil. A stylized version of the Southern Cross is also shown on the Eureka Flag.