Ara is a small constellation located in the southern sky. Its name means “the altar” in Latin.
The constellation represents the altar used by Zeus and other Greek gods to swear a vow of allegiance before they went to war against Cronus and the Titans. In another Greek myth, Ara represents the altar of King Lycaon of Arcadia. Ara was one of the 88 constellations listed by the Greek astronomer Ptolemy in the 2nd century.
The constellation contains several notable deep sky objects: the Stingray Nebula, the open cluster NGC 6193 and the globular cluster NGC 6397.
FACTS, LOCATION & MAP
Ara is among the smaller constellations (63rd in size), occupying an area of 237 square degrees. It lies in the third quadrant of the southern hemisphere (SQ3) and can be seen at latitudes between +25° and -90°. The neighboring constellations are Apus, Corona Australis, Norma, Pavo, Scorpius, Telescopium, and Triangulum Australe.
The constellation Ara has seven stars with known planets and no Messier objects. The brightest star in the constellation is Beta Arae. There are no meteor showers linked to this constellation.
Ara belongs to the Hercules family of constellations, together with Aquila, Centaurus, Corona Australis, Corvus, Crater, Crux, Cygnus, Hercules, Hydra, Lupus, Lyra, Ophiuchus, Sagitta, Scutum, Serpens, Sextans, Triangulum Australe, and Vulpecula.
There are several myths associated with the constellation. In one of them, Ara represents the altar on which Zeus and other gods vowed to defeat the Titans and overthrow Cronus, who ruled the universe. Cronus was one of the 12 Titans who had deposed his father Uranus, the previous ruler.
When a prophecy said that the same fate would befall Cronus and he would be defeated by one of his own children, to prevent it from happening, he swallowed all his children – Hestia, Demeter, Hera, Hades, and Poseidon – all of them future gods and goddesses. When the youngest child, Zeus, was born, his mother Rhea hid him in Crete and gave Cronus a stone to swallow, telling him the stone was Zeus.
When Zeus grew up, he made Cronus vomit his brothers and sisters. Once freed, they swore to overthrow Cronus and the Titans. The war between the gods and the Titans lasted a decade and the gods won in the end. Zeus became the god of the sky, ruling from Olympus, Poseidon became the god of the sea, and Hades the ruler of the underworld. Zeus placed the altar among the stars to commemorate the gods’ victory.
In another story, Ara represents the altar of Lycaon, the king of Arcadia who decided to test Zeus by serving him a meal of a dismembered child, and later tried to kill the god while he slept. Zeus, enraged, transformed Lycaon into a wolf and killed his 50 sons with lightning bolts. In one version of the tale, the sacrificed child was Arcas, the son of Zeus and Lycaon’s daughter Callisto.
MAJOR STARS IN ARA
β Arae (Beta Arae)
Beta Arae is an orange K-type bright giant (possibly supergiant), approximately 603 light years distant. With an apparent magnitude of 2.84, it is the brightest star in the Ara constellation.
α Arae (Alpha Arae)
Alpha Arae, the second brightest star in Ara, is a variable Be star, a B-type star with prominent emission lines of hydrogen in its spectrum. Its apparent magnitude varies between 2.76 and 2.90.
Alpha Arae is approximately 240 light years from Earth.
It rotates very quickly (estimated speed at the equator is 470 km/s) and, as a result of this, the star is surrounded by an equatorial disk of ejected material.
γ Arae (Gamma Arae)
Gamma Arae is a blue-white B-type supergiant, approximately 1140 light years distant. It has a visual companion 17.9 arcseconds away. The companion is a white A-type main sequence dwarf. Gamma Arae has an apparent magnitude of 3.5.
ζ Arae (Zeta Arae)
Zeta Arae is another orange K-type giant, about 574 light years distant. It has an apparent magnitude of 3.12.
μ Arae (Mu Arae)
Mu Arae (HD 160691) is a main sequence G-type star that has four known planets in its orbit. It is approximately 50 light years distant and has an apparent magnitude of 5.12. Three of the four planets in the star’s orbit have masses similar to that of Jupiter.
ε Arae (Epsilon Arae)
Epsilon Arae is a binary star system. Epsilon-1 Arae has an apparent magnitude of 4.06 and is about 300 light years distant. It is an orange K-type giant.
Epsilon-2 Arae is a binary star, 85.9 light years away, with an apparent magnitude of 5.27. The primary component is a yellow-white F-type main sequence dwarf. The closer companion star is only 0.6 arcseconds away and has an apparent magnitude of 8.6. The system has a third component, a 13th magnitude star that lies 25 arcseconds away from the primary star.
DEEP SKY OBJECTS IN ARA
NGC 6193 is a large open cluster that contains 27 stars, many of them binaries. The cluster lies eight degrees west and one degree north of Alpha Arae. Its estimated age is 3 million years.
The two hottest stars in the cluster are responsible for the illumination of NGC 6188, an emission nebula also located in Ara constellation.
NGC 6193 has a visual magnitude of 5.2, is 15′ in diameter, and lies approximately 4,300 light years from Earth.
NGC 6379 is a bright globular star cluster located three degrees to the northeast of Beta Arae. It contains about 400,000 stars.
The cluster is approximately 7,200 light years distant, which makes it one of the nearest globular clusters to us.
It was first discovered in the mid-18th century by the French astronomer Nicolas Lacaille.
The cluster is notable for the number of blue stragglers it contains. (Blue stragglers are main sequence stars that are bluer, two to three times more massive, and a few magnitudes above the stars at the main sequence turn-off point for the cluster.)
The Stingray Nebula (Hen 3-1357)
The Stingray Nebula is a planetary nebula approximately 18,000 light years from Earth. It is the youngest planetary nebula known.
The central star is a white dwarf that has a companion 0.3 arcseconds away. The nebula has an apparent magnitude of 10.75.
Even though it is significantly smaller than most other planetary nebulae discovered so far, the Stingray Nebula is 130 times larger than our solar system.
NGC 6362The globular cluster NGC 6362 has an apparent magnitude of 8.3 and lies at a distance of about 24,800 light years from Earth. It is located near the border with the constellation Apus.
NGC 6362 was discovered by the British astronomer James Dunlop on June 30, 1826.
The cluster is estimated to be 13.57 billion years old and composed mostly of evolved red giant stars. It also contains a number of blue stragglers, stars that appear younger than they really are. These stars are bluer and more luminous than their neighbours either because they were formed in collisions of two old stars or because they have stolen mass from their companions.