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Octans, a constellation for August and all months

Contributed by Paul Rodmell, Southland Astronomical Society

OCTANS, the OCTANT, Pronounced OCK-tanz

Chart showing the constellations.

Octans (originally Octans Hadleianus) was established by Nicolas Louis de Lacaille in 1752 to commemorate the invention of the octant (a navigational instrument before the sextant) by John Hadley in 1730. It occupies the rather barren region around the south celestial pole - the point in the sky about which the stars appear to rotate. The stars are not designated in magnitude sequence, for the brightest is the magnitude 3.8 orange-yellow ν Octantis, while α Oct is only magnitude 5.1.

Unlike the northern hemisphere, there is no bright star like Polaris to mark the present position of the south Celestial Pole. The nearest star is the dim magnitude 5.5 σ Octantis, which is just over 1° from the pole.

To find Octans look towards the south half way up the sky. Octans is about half way from the Pointers to the Southern Cross and Achernar (the bright star that the Cross appears to point to). Or alternatively extent the long arm of the Cross about three times.

Chart showing Octans, and Constellations round the S Pole - as seen about 9.00 pm mid August.

Octans. 10.6 kb

Constellation Grus Constellation Indus Constellation Pavo Triangulum Australe Constellation Apus Constellation Circinus Constellation Centaurus Constellation Crux Constellation Musca Constellation Vela Constellation Carina Constellation Volans Constellation Chamaeleon Constellation Mensa Constellation Dorado Constellation Hydrus Constellation Horologium Constellation Reticulum Constellation Eridanus Constellation Tucana Constellation Phoenix

Some stars in the Constellation

α Octantis is a magnitude 5.1 white star 148 light years away.

β Oct is a magnitude 4.2 white star 140 light years away.

δ Oct is a magnitude 4.3 orange giant star 112 light years away.

θ Oct is a magnitude 4.8 orange giant star 221 light years away.

λ Oct is a pair of stars 36 light years away shining at magnitudes 5.5 and 7.6, individually visible in small telescopes. It appears to be a long period binary, with the only change being slow retrograde motion since John Herschel's measures in 1836. The system lies 435 light years away.

ν Oct is a magnitude 3.8 orange giant star 69 light years away. It is the brightest star in the constellation.

σ Oct (Polaris Australis) with a magnitude 5.4 is the rather faint Pole Star for Southern skies.

Visibility

Being the pole constellation, Octans is visible all year in the Southern hemisphere. Its orientation in the sky will gradually rotate throughout the year. The main part of the constellation is highest in mid evening during August and September.


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