Octans () is a faint constellation located in the deep

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

. Its name is

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power ...

for the eighth part of a circle, but it is named after the octant, a

navigational instrument Navigational instruments are instruments used by nautical navigators and pilots as tools of their trade. The purpose of navigation is to ascertain the present position and to determine the speed, direction, etc. to arrive at the port or point of d ...

. Devised by French

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either o ...

Nicolas Louis de Lacaille Abbé Nicolas-Louis de Lacaille (; 15 March 171321 March 1762), formerly sometimes spelled de la Caille, was a French astronomer and geodesist who named 14 out of the 88 constellations. From 1750 to 1754, he studied the sky at the Cape of Good ...

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 celestial sphere, sky, bordered by arcs of right ascension and declination. Together they cover the ...

. 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 a ...

is located within the boundaries of Octans.

History and mythology

Octans was one of 14 constellations created by French astronomer

during his expedition to the

Cape of Good Hope The Cape of Good Hope ( af, Kaap die Goeie Hoop ) ;''Kaap'' in isolation: pt, Cabo da Boa Esperança is a rocky headland on the Atlantic coast of the Cape Peninsula in South Africa. A common misconception is that the Cape of Good Hope is ...

, 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 half of the celestial sphere; that is, it lies south of the celestial equator. This arbitrary sphere, on which seemingly fixed stars form constellations, appear ...

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

Age of Enlightenment The Age of Enlightenment or the Enlightenment; german: Aufklärung, "Enlightenment"; it, L'Illuminismo, "Enlightenment"; pl, Oświecenie, "Enlightenment"; pt, Iluminismo, "Enlightenment"; es, La Ilustración, "Enlightenment" was an intel ...

. 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 English usually refers to: * English language * English people English may also refer to: Peoples, culture, and language * ''English'', an adjective for something of, from, or related to England ** English national id ...

mathematician

John Hadley John Hadley (16 April 1682 – 14 February 1744) was an English mathematician, and laid claim to the invention of the octant, two years after Thomas Godfrey claimed the same. Biography He was born in Bloomsbury, London the eldest son of ...

, 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 very faint constellation; its brightest member is Nu Octantis, a

spectral class In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting th ...

K1 III

giant star A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...

with an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

3.73. It is 63.3 ± 0.8

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 101 ...

s distant from Earth.

Beta Octantis Beta Octantis, Latinized from β Octantis, is a probable astrometric binary star system in the southern circumpolar constellation of Octans. It is faintly visible to the naked eye with an apparent visual magnitude of 4.13. Based upon an ...

is the second brightest star in the constellation.

Sigma Octantis Sigma Octantis is a solitary star in the Octans constellation that forms the pole star of the Southern Hemisphere. Its name is also written as σ Octantis, abbreviated as Sigma Oct or σ Oct, and it is officially named Polaris Australi ...

, the southern

pole star A pole star or polar star is a star, preferably bright, nearly aligned with the axis of a rotating astronomical body. Currently, Earth's pole stars are Polaris (Alpha Ursae Minoris), a bright magnitude-2 star aligned approximately with its ...

, 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. Conveniently for navigators, there are other, much easier methods for locating the southern celestial pole. For example, the constellation

Crux Crux () is a constellation of the southern sky that is centred on four bright stars in a cross-shaped asterism commonly known as the Southern Cross. It lies on the southern end of the Milky Way's visible band. The name ''Crux'' is Latin for ...

, the Southern Cross, currently points toward the south celestial pole, if one draws a line from

Gamma Crucis Gacrux it is the third-brightest star in the southern constellation of Crux, the Southern Cross. It has the Bayer designation Gamma Crucis, which is Latinised from γ Crucis and abbreviated Gamma Cru or γ Cru. With an apparent visual ma ...

Alpha Crucis Acrux is the brightest star in the southern constellation of Crux. It has the Bayer designation α Crucis, which is Latinised to Alpha Crucis and abbreviated Alpha Cru or α Cru. With a combined visual magnitude of +0.76, it is the 1 ...

. Another method includes an asterism made up of Sigma,

Chi Chi or CHI may refer to: Greek *Chi (letter), the Greek letter (uppercase Χ, lowercase χ); Chinese * ''Chi'' (length) (尺), a traditional unit of length, about ⅓ meter * Chi (mythology) (螭), a dragon * Chi (surname) (池, pinyin: ''chí ...

Tau Tau (uppercase Τ, lowercase τ, or \boldsymbol\tau; el, ταυ ) is the 19th letter of the Greek alphabet, representing the voiceless dental or alveolar plosive . In the system of Greek numerals, it has a value of 300. The name in English ...

, and Upsilon Octantis, which form a distinctive

trapezoid A quadrilateral with at least one pair of parallel sides is called a trapezoid () in American and Canadian English. In British and other forms of English, it is called a trapezium (). A trapezoid is necessarily a convex quadrilateral in Eucli ...

shape. 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 nine and a half times that of Earth. It has only one-eighth the average density of Earth; ...

, which is the magnitude 4.3

Delta Octantis δ Octantis, Latinised as Delta Octantis, has the distinction of being Saturn's southern pole star. An orange giant of class K2III, it has 1.2 times the mass of the Sun and about 25 times the Sun's radius. This star is about 4.3 billion ...

. The

Astronomical Society of Southern Africa The Astronomical Society of Southern Africa (ASSA), formed in 1922, is a widespread body consisting of both amateur and professional astronomers. There are eight autonomous centres throughout Southern Africa. History The Cape Astronomical Associ ...

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 T, or t, is the twentieth letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''tee'' (pronounced ), plural ''tees''. It is der ...

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

HD 142022 HD 142022 is a binary star system located in the southernmost constellation of Octans. It is too faint to be visible to the naked eye, having an apparent visual magnitude of 7.70. The distance to this system is based on parallax, but it ...

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 but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere temp ...

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, and generally affect both the motions of stars and interstellar gas within spiral galaxies ...

that happens to be the closest

NGC object The ''New General Catalogue of Nebulae and Clusters of Stars'' (abbreviated NGC) is an astronomical catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, including galaxies, star clusters and ...

to the

south 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 ...

. 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 up 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 maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

during

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

Notes

References

;Citations ;References * *

External links

The Deep Photographic Guide to the Constellations: Octans

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