Octans constellation is located in the southern celestial hemisphere. It was named after the octant, a navigational instrument. Its name denotes the eighth part of a circle in Latin. Due to its location in the far southern sky, the constellation is invisible to observers in the northern hemisphere.
Octans was introduced by the French astronomer Nicolas Louis de Lacaille in the 18th century. It does not have any bright stars or any deep sky objects that are bright enough for small telescopes.
Octans contains the south celestial pole. It is home to the South Star, Sigma Octantis (Polaris Australis), which is too faint to be a useful marker of true south. The constellation also hosts Polarissima Australis (NGC 2573), the nearest New General Catalogue object to the southern celestial pole.
Facts, location and map
Octans is the 50th constellation in size, occupying an area of 291 square degrees of the far southern sky. It lies in the fourth quadrant of the southern hemisphere (SQ4). The entire constellation is visible from locations between the latitudes between +0° and -90°. The neighboring constellations are Apus, Chamaeleon, Hydrus, Indus, Mensa, Pavo and Tucana.
The constellation name Octans is pronounced /ˈɒktænz/. In English, the constellation is known as the Octant. The genitive form of Octans, used in star names, is Octantis (pronunciation: /ɒkˈtæntɪs/). The three-letter abbreviation, adopted by the International Astronomical Union (IAU) in 1922, is Oct.
Octans belongs to the Lacaille family of constellations, along with Antlia, Caelum, Circinus, Fornax, Horologium, Mensa, Microscopium, Norma, Pictor, Reticulum, Sculptor, and Telescopium.
Nu Octantis, the brightest star in the constellation, is an orange subgiant that shines at magnitude 3.73 from a distance of 73.5 light-years.
The nearest star in Octans, Gliese 877, is a red dwarf located 28.041 light-years away. It is the only star in the constellation that lies within 10 parsecs of the Sun.
Octans contains at least four stars with known planets and does not have any Messier objects. There are no meteor showers associated with the constellation.
The constellation hosts one formally named star. The star name approved by the International Astronomical Union (IAU) is Polaris Australis (Sigma Octantis).
Octans constellation map by IAU and Sky&Telescope magazine (Roger Sinnott & Rick Fienberg) (CC BY 3.0)
Story
The constellation Octans was created by the French astronomer Nicolas Louis de Lacaille in 1752. In the 1750s, Lacaille spent a year studying the southern night sky from the Cape of Good Hope in South Africa. He observed nearly 10,000 stars and created 14 new constellations, including Octans. His catalogue of the southern skies, Coelum Australe Stelliferum, was published in 1763.
Lacaille presented his map of the southern constellations to the French Royal Academy of Sciences in 1754, and his constellations soon became widely adopted. Most of them were named after scientific instruments associated with the Age of Enlightenment. There are no myths associated with them.
Lacaille created Octans out of dim circumpolar stars around the south celestial pole and originally named the constellation l’Octans de Reflexion, or “the reflecting octant,” which was the precursor to the modern sextant. The French astronomer described the octant as “the main instrument of navigators for observing the altitude of the pole.”
When he created the constellation, Lacaille used several stars from the neighbouring constellations Hydrus and Apus, introduced by Dutch navigators in the late 16th century. He first depicted Octans on a star chart published in 1756.
In Europe, the constellation was known as Octans Hadleianus, after John Hadley, the English mathematician who invented the octant in 1730. The German astronomer Johann Elert Bode called the constellation Octans Nautica in his star atlas Uranographia of 1801.
Octans stars
Octans contains around 60 visible stars (brighter than magnitude 6.5), 22 of which have Bayer designations.
Nu Octantis, the constellation’s lucida, is the only star in Octans brighter than magnitude 4.0. It forms an elongated triangle with Beta and Delta Octantis.
ν Octantis (Nu Octantis)
Nu Octantis (ν Oct) is a spectroscopic binary system composed of an orange subgiant (K1IV) and a white dwarf. It lies 73.5 light-years away. With an apparent magnitude of 3.73, it is the brightest point of light in Octans. Even though it has the Bayer designation Nu Octantis, it is more than a magnitude brighter than Alpha Octantis.
Nu Octantis A and B orbit each other with a period of 1050.74 days at a separation of 2.61 astronomical units.
The primary component has a mass of 1.57 solar masses and a radius 5.04 times that of the Sun. It shines with a luminosity of 13.2 Suns with a surface temperature of 4,811 K. The star is much younger than the Sun, with an estimated age of 2.70 billion years.
The white dwarf companion has a mass of 0.57 solar masses. It was originally the more massive of the two stars and evolved faster due to its higher mass.
Nu Octantis A hosts an orbiting exoplanet, Nu Octantis Ab. First reported by David J. Ramm in 2004, the planet was later disputed but ultimately confirmed in 2025. It is a gas giant with a mass of 2.19 Jupiter masses that orbits the parent star with a period of 402.4 days at a distance of 1.24 AU.
Nu Octantis Ab has an unusual orbit, which lies halfway between Nu Octantis A and B.
β Octantis (Beta Octantis)
Beta Octantis (β Oct) is the second brightest star in Octans. It has the spectral class A9IV-V, indicating a bluish white star that shows characteristics of both a main sequence and a subgiant star.
The star shines at magnitude 4.13 from an approximate distance of 149 light-years. It has 2.27 times the Sun’s mass and a radius of 3.2 solar radii. With an effective temperature of 8,006 K, it is 42 times more luminous than the Sun. The star is believed to be 496 million years old.
δ Octantis (Delta Octantis)
Delta Octantis (δ Oct) is an orange giant star of the spectral type K2III. It has an apparent magnitude of 4.31 and is approximately 299 light years distant from the solar system.
The star has a mass 1.06 times that of the Sun and a radius 25 times solar. It has an estimated age of 4.3 billion years, similar to the Sun’s.
Delta Octantis is notable for being the southern pole star of Saturn.
θ Octantis (Theta Octantis)
Theta Octantis (θ Oct) is a red clump giant with the stellar classification K3III. It has an apparent magnitude of 4.78 and is approximately 217 light years distant from the Sun.
The star has a mass 120% that of the Sun. As it evolved away from the main sequence, it has expanded to a size of 15.84 solar radii. It shines with 79.2 solar luminosities and has a surface temperature of 4,325 K.
ε Octantis (Epsilon Octantis)
Epsilon Octantis (ε Oct) is a faint red giant on the asymptotic giant branch (AGB). With an effective temperature of 3,560 K, it has the spectral type M5III. It lies 291 light-years away.
The star has a mass of 1.34 solar masses and an energy output of 1,819 Suns. It has a radius of around 112 solar radii.
Epsilon Octantis is classified as a semiregular variable star. It shines at magnitude 5 and its brightness has been observed to vary from magnitude 4.58 to 5.30.
γ Octantis (Gamma Octantis)
Three stars share the Bayer designation Gamma Octantis (γ Oct). These stars appear in the same line of sight but are not physically related. All three are visible to the unaided eye in good conditions, away from light pollution.
γ1 Octantis (Gamma1 Octantis)
Gamma1 Octantis is a yellow giant with an apparent magnitude of 5.10, located 268 light years away. It is a red clump star. It has undergone a helium flash and is now fusing helium at its core. It has a mass of 1.81 solar masses, a radius 10.3 times that of the Sun, and a luminosity of 60 Suns.
γ2 Octantis (Gamma2 Octantis)
Gamma2 Octantis is an orange giant located 320 light years away. It shines at magnitude 5.72. Like Gamma1, it is a red clump giant. It has 115% of the Sun’s mass and has expanded to a size of around 10.54 solar radii. It shines with 52.6 solar luminosities.
γ3 Octantis (Gamma3 Octantis)
Gamma3 Octantis is an orange giant located 264 light years away. With an apparent magnitude of 5.28, it is brighter than Gamma2 but fainter than Gamma1 Octantis. The evolved star is currently on the horizontal branch (HB). Its main source of energy is helium fusion in the core and hydrogen fusion in a shell around the core.
Gamma3 Octantis is the smallest and most massive of the three Gamma stars. It has 2.23 times the Sun’s mass and a radius of just under 10 solar radii. It is 50.5 times more luminous than the Sun.
The three Gamma Octantis stars, image credit: ESO/Digitized Sky Survey 2 (CC BY 4.0)
α Octantis (Alpha Octantis)
Alpha Octantis (α Oct) is a double-lined spectroscopic binary star system composed of two yellow-white F-type giant stars located 145 light-years away. The system has an apparent magnitude of 5.13. The components have the spectral types F4III and F5III. They have an orbital period of 9.073 days.
The Alpha Octantis system is classified as a Beta Lyrae-type eclipsing binary system. It is a close binary system that varies in brightness because the components block each other’s light as they orbit around the common centre of mass. The primary eclipse causes a decrease in brightness by 0.04 magnitudes. Beta Lyrae-type stars are usually in such close orbit that their shapes are distorted by each other’s gravitational forces, and they typically have ellipsoidal shapes.
λ Octantis (Lambda Octantis)
Lambda Octantis (λ Oct) is a faint binary star located 398 light years away. It has an apparent magnitude of 5.27. Individually, the two components shine at magnitudes 5.64 and 7.25.
The primary component, Lambda Octantis A, is a giant star of the spectral type G8-K0III and the fainter companion, Lambda Octantis B, is a chemically peculiar Am star at a separation of 3.233 arcseconds from the component A. The system has an estimated age of 200 million years.
Polaris Australis – σ Octantis (Sigma Octantis)
Polaris Australis, Sigma Octantis (σ Oct), is currently the South Star, the nearest visible star to the southern celestial pole. Its northern counterpart, Polaris (the North Star), lies in Ursa Minor.
Unlike Polaris, which is easily visible even from light-polluted areas, Polaris Australis is too dim to be used in navigation. With an apparent magnitude of 5.47, it is barely visible even in good conditions. For this reason, the star is not commonly used to find true south. Instead, the position of the south celestial pole can be determined using the bright stars of the Southern Cross, or Hadar and Achernar.
Sigma Octantis is an evolved star larger and more massive than the Sun. It is a yellow-white subgiant or giant star located approximately 294 light-years away. It has a mass of 1.59 solar masses and a radius 4.4 times that of the Sun. With a surface temperature of 7,415 K, it shines with 44 solar luminosities. It has an estimated age of 912 million years.
The star is classified as a Delta Scuti variable. Its brightness varies by 0.03 magnitudes with a period of 2.33 hours. The variations are caused by both radial and non-radial pulsations of its surface.
Delta Scuti stars follow a period-luminosity relation. Their luminosity is linked to their pulsation period. This makes them useful as standard candles for determining the distances to deep sky objects such as globular and open star clusters and the Galactic Centre.
A trapezoidal asterism within the constellation Octans, useful for locating Sigma Octantis. Image credit: Conrad Leviston (PD)
μ2 Octantis (Mu2 Octantis)
Mu2 Octantis (μ2 Oct) is a binary system composed of two Sun-like yellow dwarfs located approximately 130 light-years away. The two components are separated by 932 astronomical units. They have apparent magnitudes of 6.5 and 7.2. Both stars are slightly larger and more massive than the Sun.
The primary component, Mu2 Octantis A, hosts a system of two orbiting exoplanets, discovered in 2012 and 2025 using the radial velocity method. The inner planet, HD 196067 c, has a mass of 10.4 Earth masses and orbits the host star with a period of 4.6 days. The outer planet, HD 196067 b, has a mass of 11.4 Jupiter masses and an orbital period of 3413.7 days.
HD 142022
HD 142022 is a binary system located 111.70 light-years away. The primary component is a main sequence or subgiant star of the spectral type G9IV-V, and the companion is a red dwarf with the stellar classification M1V. The stars have apparent magnitudes of 7.70 and 11.19, making them invisible to the unaided eye.
The primary star has 97.2% of the Sun’s mass and a radius of 1.028 solar radii. It is much older than the Sun, with an estimated age of 7.667 billion years. It has a planetary companion, discovered in 2005. The planet has a mass of at least 4.5 Jupiter masses and orbits the star at a distance of almost 3 astronomical units.
The secondary component has a mass of 0.60 solar masses and a radius of 0.56 solar radii. It shines with only 6.3 percent of the Sun’s luminosity.
HD 212301
HD 212301 is a binary star composed of a yellow-white main sequence star of the spectral type F8V and a red dwarf with the spectral class M3V. The system lies 177.2 light-years away.
The primary component hosts an orbiting hot Jupiter candidate, discovered in 2005. The planet orbits the star with a period of 2.25 days at a distance of 0.0341 AU. It has a minimum mass of 0.45 Jupiter masses.
LHS 475
LHS 475 is a red dwarf located 40.71 light-years away. With an apparent magnitude of 12.69, it is well below unaided eye visibility. It has only about 27 percent of the Sun’s mass and a radius of 0.2789 solar radii.
The small, faint star hosts the first planet confirmed by the James Webb Space Telescope (JWST). The planet was initially detected by the Transiting Exoplanet Survey Satellite (TESS), and Webb captured its transmission spectrum in August 2022.
LHS 475 b is a terrestrial planet with 91% of the Earth’s mass and a radius of 0.99 Earth radii. It takes around 2 days to complete an orbit around its host star. Astronomers believe that it is likely tidally locked, which is to say that it always faces LHS 475 with the same side.
This illustration reflects that exoplanet LHS 475 b is rocky and almost precisely the same size as Earth based on new evidence from NASA’s James Webb Space Telescope. The planet is only a few hundred degrees warmer than our home planet. The planet whips around its star in just two days, far faster than any planet in the solar system, but its red dwarf star is less than half the temperature of the Sun. Image credit: NASA, ESA, CSA, Leah Hustak (STScI) (PD)
Deep sky objects in Octans
Octans does not contain any bright deep sky objects listed in the Messier, Caldwell and Herschel 400 catalogues. It hosts several faint galaxies listed in the New General Catalogue (NGC).
NGC 7098
NGC 7098 is a double barred spiral galaxy with an apparent magnitude of 11.3, located 95 million light years away. With an apparent size of 4 by 2.6 arcminutes, it may be spotted in larger amateur telescopes.
With a diameter of 152,400 light-years, NGC 7098 is similar in size to the Andromeda Galaxy. It was discovered by the British astronomer John Herschel from South Africa on September 22, 1835.
Approximately 95 million light-years away, in the southern constellation of Octans (The Octant), lies NGC 7098 — an intriguing spiral galaxy with numerous sets of double features. The first of NGC 7098’s double features is a duo of distinct ring-like structures that loop around the galaxy’s hazy heart. These are NGC 7098’s spiral arms, which have wound themselves around the galaxy’s luminous core. This central region hosts a second double feature: a double bar. Image credit: ESO (CC BY 4.0)
NGC 7095
NGC 7095 is a barred spiral galaxy located 114.5 million light-years away. It has an apparent magnitude of 12.23 and an angular size of 2.8 by 2.7 arcminutes. It appears within the elongated triangle formed by Nu, Beta, and Delta Octantis, just north of Beta Octantis.
The galaxy was discovered by John Herschel on September 21, 1837.
NGC 7095, credit: Legacy Surveys / D.Lang (Perimeter Institute) & Meli Thev (CC BY 4.0)
NGC 7637
NGC 7637 is a spiral galaxy located 178.5 million light years away. It has an apparent magnitude of 13 and an apparent size of 2.1 by 1.9 arcminutes. John Herschel discovered it on October 17, 1835.
The galaxy hosted three supernovae observed in the last several decades: SN 1992ao (Type II) in 1992, SN 2012ah (Type Ia) in 2012, and SN 2022iwt (Type II) in 2022.
NGC 7637, credit: Legacy Surveys / D.Lang (Perimeter Institute) & Meli Thev (CC BY 4.0)
LEDA 10922
LEDA 10922 (PGC 10922) is a faint lenticular galaxy located at a distance of 200 million light years. It was captured by Hubble in 2013.
The NASA/ESA Hubble Space Telescope has captured this image of PGC 10922, an example of a lenticular galaxy — a galaxy type that lies on the border between ellipticals and spirals. Seen face-on, the image shows the disc and tightly-wound spiral structures of dark dust encircling the bright centre of the galaxy. There is also a remarkable outer halo of faint wide arcs or shells extending outwards, covering much of the picture. These are likely to have been formed by a gravitational encounter or even a merger with another galaxy. Some dust also appears to have escaped from the central structure and has spread out across the inner shells.
An extraordinarily rich background of more remote galaxies can also be seen in the image. Image credit: ESA/Hubble & NASA; Acknowledgement: Judy Schmidt (PD)
Polarissima Australis (NGC 2573)
NGC 2573 is a barred spiral galaxy approximately 84 million light-years away. With a diameter of 77,800 light-years, it is smaller than the Milky Way. As the nearest NGC object to the southern celestial pole, the galaxy has been nicknamed Polarissima Australis. It was discovered by John Herschel on March 29, 1837.
The galaxy has a northern counterpart, Polarissima Borealis (NGC 3172), a faint lenticular galaxy that appears near Polaris in Ursa Minor.