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Vathorz Posterior

Theta Carinae

One of a pair of stars in Carina that share the name Vathorz, the other being Upsilon Carinae or Vathorz Prior. The two stars are distinguished as 'Prior' and 'Posterior' because Vathorz Prior lies somewhat to the west of Vathorz Posterior, and therefore rises and sets earlier. Apart from their shared name, and the fact that they form an east-west line through Carina, the stars are not related to one another.

Vathorz Posterior is by far the brightest member of an open cluster of stars designated Caldwell 102, also called the Southern Pleiades or sometimes the Theta Carinae Cluster after their brightest member (Theta Carinae being Vathorz Posterior's Bayer designation). Seen from Earth, Vathorz Posterior appears to lie near the centre of the cluster, though in fact it is on the nearer edge, at a distance of about 460 light years from the Solar System.

This star is something of a curiosity, as it appears to be rather younger than most of its fellow members of the Southern Pleiades. The reason for this is not entirely clear, but one possibility is that it was formed some thirty million years ago by the merging of two other stars within the cluster.

Vathorz Posterior is a hot blue star, rather larger than the Sun and very considerably more luminous. It shows some small variability in its brightness, which is thought to be due to variations on the star's surface, probably caused by areas unusually rich in silicon.

The etymology of the name Vathorz is curious and unusual. It is generally credited as being from Old Norse, the language of the Vikings, or actually from a hybrid of Old Norse and Greek: vatn meaning 'water' and orizont 'level' or 'line', hence 'waterline'. Since the stars with this name form a line within the constellation of Carina the Keel, this derivation does make some sense.

It is a little perplexing, however, to find a name derived from the language of the Vikings so far south in the sky, since neither of the stars named Vathorz is visible from the northern hemisphere. This suggests that the name may be a relatively modern coinage, or perhaps that it might have an alternative derivation (say from Greek vathos, 'depth') though all sources seem to agree on an Old Norse origin for the name.


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