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The Altar

Constellation of the southern sky

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Constellation FamilyHercules
Celestial QuadrantPrimarily SQ3, extending into SQ4
Right Ascension16h37m to 18h12m
Declination-67.7° to -45.7°
Area (sq deg)237
Brightest StarBeta Arae
Optimum VisibilityJune / July (Usually visible from southern latitudes)
NotesA group of stars lying on the band of the Milky Way, southward of the tail of Scorpius the Scorpion. Ara contains several notable star clusters, including the nebulous open cluster C82. The Sun-like star Mu Arae is known as Cervantes, and is known to host a system of at least four planets.
Map of Ara Map of Ara


Relative Galactic Position of Ara

The constellation of Ara describes a region towards the centre of our galaxy, and somewhat 'below' the galactic plane.

As a far southern constellation, Ara is today almost invisible from Europe at any time of the year. Between 2,000 and 3,000 years ago, though, it was clearly visible from southern Europe and northern Africa during the summer months. The Greeks of that time called it Thytérion or Thysiastérion, the Altar of Sacrifice, perhaps because it rose in the sky at a propitious time of the year. This tradition was inherited by the Romans, who gave the constellation the name we know today: 'Ara' is the Latin word for 'Altar'.


There are few bright stars in this region of the sky. The two brightest, Alpha and Beta Arae, are coincidentally almost exactly the same magnitude of +2.8. Though the Beta star is almost 400 light years beyond the Alpha, it is much more luminous.

Some of Ara's stars are very distant: both Gamma Arae and Theta Arae lie more than 1,000 light years away, but both of these stars are brilliant supergiants, and so are clearly visible to the naked eye of an observer on Earth.

Star Clusters

The most notable cluster in Ara is a Globular group that lies somewhat 'below' the plane of the galactic disc. C86 is a fairly loose ball of stars lying approximately 7,000 light years (about 2,000 parsecs) from Earth's Solar System.

A little nearer to Earth, at about 4,500 light years distance, is an open star cluster, C82 or NGC 6193. This is quite a young cluster on a cosmic timescale, and still surrounded by much of its original nebulous material.


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