Octans is a faint

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

located in the deep Southern Sky. Its name is

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

for the eighth part of a circle, but it is named after the octant, a navigational instrument. Devised by French

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

Nicolas Louis de Lacaille in 1752, Octans remains one of the

88 modern constellations In contemporary astronomy, 88 constellations are recognized by the International Astronomical Union (IAU). Each constellation is a region of the sky bordered by arcs of right ascension and declination, together covering the entire celestial sph ...

. The southern

celestial pole The north and south celestial poles are the two points in the sky where Earth's axis of rotation, indefinitely extended, intersects the celestial sphere. The north and south celestial poles appear permanently directly overhead to observers at ...

is located within the boundaries of Octans.

History and mythology

Octans was one of 14 constellations created by French astronomer Nicolas Louis de Lacaille during his expedition to the

Cape of Good Hope The Cape of Good Hope ( ) is a rocky headland on the Atlantic Ocean, Atlantic coast of the Cape Peninsula in South Africa. A List of common misconceptions#Geography, common misconception is that the Cape of Good Hope is the southern tip of Afri ...

, and was originally named ''l’Octans de Reflexion'' (“the reflecting octant”) in 1752, after he had observed and catalogued almost 10,000 southern stars during a two-year stay at the

. He devised fourteen new constellations in uncharted regions of the

Southern Celestial Hemisphere The southern celestial hemisphere, also called the Southern Sky, is the Southern Hemisphere, southern half of the celestial sphere; that is, it lies south of the celestial equator. This arbitrary sphere, on which seemingly fixed stars form cons ...

not visible from Europe. All but one honoured instruments that symbolised the

Age of Enlightenment The Age of Enlightenment (also the Age of Reason and the Enlightenment) was a Europe, European Intellect, intellectual and Philosophy, philosophical movement active from the late 17th to early 19th century. Chiefly valuing knowledge gained th ...

. It was part of his catalogue of the southern sky, the ''Coelum Australe Stelliferum'', which was published posthumously in 1763. In Europe, it became more widely known as ''Octans Hadleianus'', in honor of English mathematician

John Hadley John Hadley (16 April 1682 – 14 February 1744) was an England, English mathematician, and laid claim to the invention of the octant (instrument), octant, two years after Thomas Godfrey (inventor), Thomas Godfrey claimed the same. Biograp ...

, who invented the octant in 1730. There is no real mythology related to Octans, partially due to its faintness and relative recentness, but mostly because of its extreme southerly latitude.

Notable features

Stars

Octans is a generally inconspicuous constellation with only one star brighter than magnitude 4; its brightest member is

Nu Octantis ν Octantis, Romanization of Greek, Latinised as Nu Octantis, is a binary star in the constellation of Octans. Unusually for having such a late greek letter in its name, it is the brightest star in this faint constellation at apparent ma ...

, a spectral class K1 III

giant star A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsp ...

with an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

3.73. It is 63.3 ± 0.8

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s distant from Earth. Beta Octantis is the second brightest star in the constellation. Polaris Australis (Sigma Octantis), the southern

pole star A pole star is a visible star that is approximately aligned with the axis of rotation of an astronomical body; that is, a star whose apparent position is close to one of the celestial poles. On Earth, a pole star would lie directly overhead when ...

, is a magnitude 5.4 star just over 1 degree away from the true south celestial pole. Its relative faintness means that it is not practical for navigation. BQ Octantis is a fainter, magnitude 6.82 star located much closer to the South Pole (at less than a degree) than Sigma. In addition to having the current southern pole star of Earth, Octans also contains the southern pole star of the planet

Saturn Saturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant, with an average radius of about 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 tim ...

, which is the magnitude 4.3 Delta Octantis. The Astronomical Society of Southern Africa in 2003 reported that observations of the

Mira variable Mira variables (named for the prototype star Mira) are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wave ...

stars R and T Octantis were urgently needed. Four star systems are known to have planets. Mu² Octantis is a binary star system, the brighter component of which has a planet.

A also has a planet orbiting. HD 142022 is a binary system, a component of which is a sunlike star with a massive planet with an orbital period of 1928 ± 46 days. HD 212301 is a yellow-white main sequence star with a

hot jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter (i.e. Jupiter analogue, Jupiter analogues) but that have very short orbital periods (). The close proximity to t ...

that completes an orbit every 2.2 days.

Deep sky objects

NGC 2573 (also known as Polarissima Australis) is a faint

barred spiral galaxy A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies in the local universe, and generally affect both the motions of stars and interstellar gas ...

that happens to be the closest NGC object to the south celestial pole. NGC 7095 and NGC 7098 are two barred spiral galaxies that are 115 million and 95 million light-years distant from Earth respectively. The sparse

open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

Collinder 411 is also located in the constellation.

Namesakes

was a stores ship used by the

United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

during

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

Notes

References

;Citations ;References * *

External links

The Deep Photographic Guide to the Constellations: Octans

{{DEFAULTSORT:Constellation, Octans Southern constellations Constellations listed by Lacaille