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Vela

The Sail

Constellation of the southern sky

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Originally part of the 'superconstellation' of Argo Navis, which was divided into three for practical purposes. Vela forms the northeastern part of Argo, with Puppis lying to the west and Carina to the south. This subdivision has had the unusual consequence of leaving Vela without an Alpha or Beta star on the Bayer system.

Map of Vela Map of Vela

The entirety of the old Argo Navis lies along the Milky Way, but Vela encompasses some of its richest and densest parts. The constellation of Vela can be located in the sky from brilliant Sirius in Canis Major, by looking southward and eastward along the band of the Milky Way beyoond the stars of Puppis (Puppis marked the Stern of Argo, while Vela was its Sail).

In the southern parts of Vela, a small asterism straddles its border with Carina. Two of Vela's stars, Alsephina and Markeb, combine with two in Carina to create the approximate shape of a cross. This shape forms a slightly fainter mirror of the more famous Southern Cross some distance to the east, and is known as the False Cross.

Stars

Vela is dense with stars across its entire area, but the main body of the Sail is formed from a quadrangle of four second-magnitude stars in the western segment of the constellation. The brightest of these is the westernmost, Suhail al Muhlif, with the red-orange Suhail falling to the north, and the pair of Alsephina and Markeb forming the Sail's southen edge.

Suhail al Muhlif is a complex system, with the heart of the system comprising two binary pairs, with other stars in more distant orbits. Most notable among the members of the system are the Gamma2 Velorum pair, which consist of a supergiant and a Wof-Rayet star. Wolf-Rayet stars (highly luminous stars rich in metals, evolving towarda a supernova eruption) are comparatively rare, and this component is the nearest and most visible such star to an observer on Earth.

Southward from Suhail al Muhlif, Vela's second brightest star is Delta Velorum, also called Alsephina or Alsafinah. Like Suhail al Muhlif, this is a complex system, with a close binary star being orbited by a third member of the same system. Another nearby binary pair is sometimes designated Delta Velorum C and D, but in fact it seems to be rather more distant than the other stars, and thus not a physical part of the Alsephina system.

Eastward of Alsephina is Vela's second member of the False Cross, the blue star Kappa Velorum or Markeb, a very close binary pair in which the stars are closer to one another than Earth's orbital distance from the Sun. The last of the four main Sail stars is red-orange Suhail or Alsuhail (Lambda Velorum, not to be confused with Suhail al Muhlif), northward of the other three. This is an immense supergiant in the later stages of its life, with a diameter some two hundred times that of the Sun.

Northward from Alsephina is a blue subgiant star designated Omicron Velorum. The star itself is only fourth magnitude, but it stands out as the brightest of an extensive open cluster, the Omicron Velorum Cluster or C85. The entire cluster contains about thirty young blue stars, spread across an area of sky some fifty arcminutes in diameter (or nearly twice the apparent diameter of the Moon's disc). The cluster has a composite magnitude of +2.6, approaching that of the star Markeb.

Vela contains several stars around which exoplanetary systems have been detected. Two of these have been allocated official names: Kalausi (HD 83443) and Natasha (HD 85390). Each of these is an orange dwarf star, and each has one known gas giant in orbit (and there are unconfirmed indications that Kalausi may also have a second planet). The confirmed gas giant planets have also received official names: Kalausi b is Buru, while Natasha b is Madalitso.

In the far east of the constellation lies an object designated Luhman 16. With a visual magnitude of +16.2, this is far, far too faint to be seen with the naked eye. The system consists of a pair of brown dwarfs, faint and cool substellar objects orbiting one another at a distance of about 3 AU. This binary system is notable as being just 6.5 light years from the Solar System, making it the third closest known system to the Sun after Alpha Centauri and Barnard's Star.

Deep Sky Objects

Most prominent among the star clusters of Vela is the Omicron Velorum Cluster mentioned above, but the constellation plays host to a range of other clusters and nebulae. Among its open clusters are those designated NGC 2547 and NGC 2670, both of which lie relatively close to the Omicron Velorum Cluster in the sky. Further eastward across the constellation is the globular cluster C79, a huge ball of stars travelling rapidly across the disc of the Galaxy. C79 is notable in that it appears to contain a black hole within its core, which is highly unusual for a cluster of this kind.

In the far north of Vela, almost exactly on its border with neighbouring Antlia, is a distinctive planetary nebula. This is C74, known as the Eight-Burst Nebula from its structure, and also the Southern Ring Nebula for its similarity to the Ring Nebula in the northern sky. The nebula is expanding out from one of a pair of central stars, and lies about 2,000 light years from the Solar System.

Centred on a point in the west of the constellation is the Gum Nebula or Gum 12. This is a faint and roughly ring-shaped patch of nebulosity, indistinct against the background of the Milky Way, but covering a wide area of the sky. The nebula is the expanding remnant of a supernova that erupted some 11,000 years ago. At its heart, the exploding star that created the nebula can still be detected as the Vela Pulsar, PSR B0833-45, an object spinning so rapidly that it flashes with beams of light and radio waves more than eleven times each second.

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