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Constellations: Antlia 'the Air Pump'

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The shield of the Science, Mathematics and Engineering faculty of the h2g2 University.Constellations: Overview | Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Boötes | Caelum
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Name:Antlia (Latin: 'air pump')
Short form:Ant
Area:239 sq deg
Co-ordinates1:Right Ascension 10h, Declination −35°

Antlia, the Air Pump is a Southern Hemisphere constellation found south of the straggling constellation Hydra which bounds its complete northern side. To its southern edge lies Vela, part of the earlier, much larger constellation Argo, which has now been split into three to form other constellations. There is no distinctive pattern to Antlia and it takes considerable imagination to see anything resembling a 'pump' here. None of Antlia's stars are brighter than +4.25 magnitude.

Antlia is one of 13 southern hemisphere constellations that remain in use today which were created and named by Abbé Nicholas Louis de la Caille (Lacaille). He mapped the far southern hemisphere skies between 1751 and 1753 from the Cape of Good Hope, Africa, and created a number of new constellations to fill in sparsely star-populated areas of sky. La Caille's constellations celebrated contemporary objects and 18th-Century wonders of the scientific world. Antlia commemorated the Air Pump devised by physicist Robert Boyle, and La Caille's name 'Antlia Pneumatica' has now become more conveniently shortened by astronomers to 'Antlia'.

Principal Stars

Due to its far south position in the sky near to the southern celestial pole, the stars of Antlia were not seen by ancient astronomers. Consequently none of its stars were ever given proper names and are therefore known only by their attributed Greek letter classification.

Despite being close to the galactic equator and adjacent to the edge of the Milky Way, Antlia covers a relatively barren part of the sky which presents few objects of interest to observers using amateur equipment. Alpha Ant is an orange giant of magnitude +4.25 at 277 light years distance. La Caille's beta Ant has now been lost to the neighbouring constellation of Hydra, while zeta Ant is a widely spaced double star, with a primary of +5.8 and a secondary of +5.9 magnitude. They are easily seen with binoculars.

The Stars of Antlia

StarNameMagnitudeDistance (light years)Remarks
α Antalpha Ant+4.25277Orange Giant
η Anteta Ant+5.2110Double: +5.2 and +12
ζ Antzeta Ant+6.0373Wide spaced binary: +5.8 and +5.9 mag

Galaxies and a Nebula

Antlia contains a number of spiral galaxies, but all are faint. One notable planetary nebula, NGC 3132 the 'Southern Ring', lies on the border with the adjacent constellation of Vela, and is more usually assigned to it. Like all planetary nebula, this is a result of a star in its dying throes expelling a shell of gas as it reduces to a 'white dwarf'. The gas is being ejected at a speed of some nine miles per second and the shell is now nearly half a light year in diameter. Remarkably there is at its centre a dark lane of gas which remains along its major axis which has only recently been revealed by photographs from the Hubble Space telescope. There is also what appears to be a binary star system at its centre, but this is a line-of-sight effect and the pair are not associated with the nebula.

In 1997 an unusual dwarf spheroidal galaxy, the Antlia Galaxy, was discovered within Antlia's borders. It is about 3.75 million light years away and is one of a small number of dwarf galaxies that are part of our local group of galaxies which includes the Andromeda Galaxy. The Antlia Galaxy is believed to be between 4,000 to 6,000 light years in diameter, but contains only about one million stars. It is unusual in that it is in a relatively isolated position from the other known dwarf galaxies, and has not been distorted by the gravity of its more massive neighbours. Another anomaly is that it does not appear to contain any hot, blue, newly-formed stars, despite an abundance of hydrogen which should provide an environment suitable for their formation.

Galaxies and Nebula Table

Catalogue NoNameTypeMagnitudeDistance (light years)
NGC 3132Southern Ring NebulaPlanetary Nebula+82,000
NGC 2997 Spiral Galaxy+1055 million
PGC 29194Antlia Dwarf GalaxyDwarf Spheroidal Galaxy+163.75 million

Extrasolar Planets

There are two extrasolar planets detected orbiting stars belonging to the Antlia constellation. HD 93083 b is a gas giant which was discovered in 2005. WASP-66 b was detected by the transit method in 2011.

1Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (−) for southern ones.

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