Sextans Constellation


Sextans constellation lies in the southern sky, near the celestial equator. It represents the astronomical sextant. It is located in a dim region of the sky between the constellations Hydra, Crater, and Leo.

Sextans was created by the Polish astronomer Johannes Hevelius in the 17th century. The constellation is a rather faint one, with only one star brighter than fifth magnitude.

Sextans contains several notable deep sky objects, among them the Spindle Galaxy (NGC 3115), the spiral galaxies NGC 3166 and NGC 3169, and the irregular galaxies Sextans A and Sextans B.

FACTS, LOCATION & MAP

sextans constellation,sextans stars,sextans star map,sextans location

Sextans Constellation Map, by IAU and Sky&Telescope magazine

Sextans is the 47th constellation in size, occupying an area of 314 square degrees.

It is located in the second quadrant of the southern hemisphere (SQ2) and can be seen at latitudes between +80° and -90°.

The neighboring constellations are Crater, Hydra and Leo.

Sextans has five stars with known planets and contains no Messier objects.

The brightest star in the constellation is Alpha Sextantis, with an apparent visual magnitude of 4.49.

There is one meteor shower associated with the constellation; the Sextantids.

Sextans belongs to the Hercules family of constellations, along with along with Aquila, Ara, Centaurus, Corona Australis, Corvus, Crater, Crux, Cygnus, Hercules, Hydra, Lupus, Lyra, Ophiuchus, Sagitta, Scutum, Serpens, Triangulum Australe and Vulpecula.


STORY

Sextans constellation is not associated with any myths. It was introduced by the Polish astronomer Johannes Hevelius in 1687.

He originally named the constellation Sextans Uraniae after the instrument he had used to measure star positions until it was destroyed in a fire at his observatory in 1679.

Even though telescopes were available to him, Hevelius preferred to use the sextans for naked-eye sightings, and continued to do so throughout his life.

MAJOR STARS IN SEXTANS

Sextans constellation, image: Till Credner

Sextans constellation, image: Till Credner

α Sextantis (Alpha Sextantis)

Alpha Sextantis is a white giant star with the stellar classification A0III. It has an apparent magnitude of 4.48 and is approximately 287 light years distant from Earth. It is the brightest star in Sextans. It is 122 times more luminous than the Sun and has a mass three times solar. The star is believed to be about 300 million years old.

Alpha Sextantis is informally considered to be an “equator star,” currently located less than a quarter of a degree south of the celestial equator. In 1900, it was 7 arcminutes north of the equator, but crossed over to the southern hemisphere in December 1923. The star lies almost exactly south of the bright star Regulus in Leo constellation, and only 0.4 arcminutes to the west.

γ Sextantis (Gamma Sextantis)

Gamma Sextantis is a triple star system in Sextans constellation. It has an apparent visual magnitude of 5.07 and is approximately 262 light years distant.

The system consists of a close binary star with the stellar classification A1. The two stars are separated by 0.38 arcseconds and have visual magnitudes of 5.8 and 6.2. They orbit each other with a period of 77.6 years.

A 12th magnitude companion orbits the binary star from a distance of 36 arcseconds.

β Sextantis (Beta Sextantis)

Beta Sextantis is a blue-white main sequence dwarf with the stellar classification B6V. It has an apparent visual magnitude of 5.0 to 5.1 and is approximately 345 light years distant.

Beta Sextantis is classified as an Alpha-2 Canum Venaticorum type variable star. It has a period of variability of around 15.4 days.

δ Sextantis (Delta Sextantis)

Delta Sextantis is a blue-white main sequence dwarf with the stellar classification of B9.5V. It has an apparent visual magnitude of 5.19 and is approximately 300 light years distant from the solar system.

ε Sextantis (Epsilon Sextantis)

Epsilon Sextantis is a yellow-white giant star belonging to the stellar class F2 III. It has an apparent magnitude of 5.25 and is approximately 183 light years distant from the Sun.

24 Sextantis

24 Sextantis is a yellow subgiant star belonging to the stellar class G5 IV. It has an apparent visual magnitude of 6.61 and is approximately 253 light years distant. The star is believed to be about 2.8 billion years old. It has 54 percent more mass than the Sun.

Two giant extrasolar planets were discovered orbiting the star in July 2010. The inner planet has twice the mass of Jupiter and orbits the star every 453 days. The outer planet has 5/6 the mass of Jupiter and orbits the star every 883 days. The planets are in a 2:1 resonance: the outer planet orbits the star once every time the inner planet completes two orbits.

LHS 292

LHS 292 is a red dwarf star in Sextans. It has the stellar classification of M6.5 V. It has an apparent visual magnitude of 15.73 and is only 14.8 light years distant from Earth. In spite of its proximity, the star cannot be seen without at least a large amateur telescope.

LHS 292 is a flare star, and its brightness can suddenly increase over short periods of time.

HD 92788

HD 92788 is a class G5 star in Sextans. It has a visual magnitude of 4.72 and is 107.1 light years distant. It is slightly smaller than the Sun and more massive. An extrasolar planet was discovered orbiting the star in 2001. It has a mass at least 3.67 times that of Jupiter and it orbits the star every 325.81 days.

HD 86081

HD 86081 is a yellow-white main sequence dwarf star with the stellar classification of F8V. It has a visual magnitude of 8.74 and is approximately 297 light years distant from Earth. The star has a luminosity 1.75 solar. A planet with at least 1.50 times the mass of Jupiter orbits the star every 2.1375 days.

lenticular galaxy,sextans

NGC 3115 – Using the Chandra image, the flow of hot gas toward the supermassive black hole in the center of this galaxy has been imaged. This is the first time that clear evidence for such a flow has been observed in any black hole. The Chandra data are shown in blue and the optical data from the VLT are colored gold. The point sources in the X-ray image are mostly binary stars containing gas that is being pulled from a star to a stellar-mass black hole or a neutron star. The inset features the central portion of the Chandra image, with the black hole located in the middle. No point source is seen at the position of the black hole, but instead a plateau of X-ray emission coming from both hot gas and the combined X-ray emission from unresolved binary stars is found. To detect the black hole’s effects, astronomers subtracted the X-ray signal from binary stars from that of the hot gas in the galaxy’s center. Then, by studying the hot gas at different distances from the black hole, astronomers observed a critical threshold: where the motion of gas first becomes dominated by the supermassive black hole’s gravity and falls inwards. The distance from the black hole where this occurs is known as the “Bondi radius.” As gas flows toward a black hole it becomes squeezed, making it hotter and brighter, a signature now confirmed by the X-ray observations. The researchers found the rise in gas temperature begins at about 700 light years from the black hole, giving the location of the Bondi radius. This suggests that the black hole in the center of NGC 3115 has a mass of about two billion times that of the Sun, supporting previous results from optical observations. This would make NGC 3115 the nearest billion-solar-mass black hole to Earth. NGC 3115 is located about 32 million light years from Earth and is classified as a so-called lenticular galaxy because it contains a disk and a central bulge of stars, but without a detectable spiral pattern. Image – X-ray: NASA, CXC, Univ. of Alabama, K. Wong et al; Optical: ESO, VLT

BD-08°2823

BD-08°2823 is an orange main sequence dwarf belonging to the stellar class K3V. It has an apparent visual magnitude of 9.86 and is approximately 137 light years distant from Earth. The star is smaller, less massive and cooler than the Sun.

Two gas giants were discovered orbiting the star in 2009. The inner planet completes an orbit every 5.60 days, and the outer one orbits the star every 237.6 days.

WASP-43

WASP-43 is an orange dwarf with the stellar classification of K7V. It has an apparent magnitude of 12.4. The star has about half the mass (58 percent) of the Sun and 0.598 times the radius. A planet, a Hot Jupiter, was discovered orbiting the star in April 2011. At the time, it was the most closely orbiting Hot Jupiter discovered.

The planet, WASP-43b, has 1.78 times the mass of Jupiter and 0.93 times Jupiter’s radius. It completes an orbit around the star every 0.813475 days.

DEEP SKY OBJECTS IN SEXTANS

Spindle Galaxy – NGC 3115 (Caldwell 53)

The Spindle Galaxy is a lenticular galaxy in Sextans.

It has an apparent visual magnitude of 9.9 and is approximately 31.6 million light years distant from Earth.

The galaxy appears almost exactly edge-on.

It is several times bigger than the Milky Way. It has a supermassive black hole at its centre.

NGC 3115 is the nearest galaxy with a billion-solar-mass black hole to Earth.

The galaxy was discovered by William Herschel on February 22, 1787.

Most of the stars in it are pretty old, and the galaxy does not have must dust and gas left for new star formation to take place.

NGC 3115 is not to be confused with Messier 102 (NGC 5866) in Draco constellation, which is also called the Spindle Galaxy.

interacting galaxies

This image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile captures the pair of galaxies NGC 3169 (left) and NGC 3166 (right). These adjacent galaxies display some curious features, demonstrating that each member of the duo is close enough to feel the distorting gravitational influence of the other. The gravitational tug of war has warped the spiral shape of one galaxy, NGC 3169, and fragmented the dust lanes in its companion NGC 3166. Image: ESO, Igor Chekalin

NGC 3169

NGC 3169 is a spiral galaxy in Sextans.

It has an apparent visual magnitude of 10.3 and is approximately 70 million light years distant.

It can be found just under the bright star Regulus in Leo constellation.

The galaxy has a distorted shape as a result of gravitational interaction with nearby galaxy NGC 3166.

Both galaxies were discovered by William Herschel in 1783.

A supernova, SN 2003cg, was discovered in the galaxy in 2003.

NGC 3166

NGC 3166 is also a spiral galaxy. It lies about 50,000 light years from NGC 3169.

The two galaxies will eventually merge into one larger galaxy.

dwarf irregular galaxy

A member of the local group of galaxies which includes the massive spirals Andromeda and our own Milky Way, Sextans A is about 4 million light years distant. The bright Milky Way foreground stars appear yellowish in this view. Beyond them lie the stars of Sextans A with young blue star clusters clearly visible. Image: D. Hunter (Lowell Observatory), Z. Levay (STScI)

Sextans A (UGCA 205)

Sextans A is a small dwarf irregular galaxy in Sextans.

It is only about 5,000 light years across.

It has a visual magnitude of 11.9 and is approximately 4.31 million light years distant from Earth.

The galaxy is located within the Local Group of galaxies.

Sextans B (UGC 5373)

Sextans B is an irregular galaxy with an apparent magnitude of 11.9.

It is approximately 4.44 million light years distant.

irregular galaxy

Sextans B, image: Hubble Space Telescope, NASA

The galaxy is located either within the Local Group or just beyond it.

Five planetary nebulae have been discovered in Sextans B.

It is one of the smallest galaxies in which planetary nebulae have been found.

Sextans B forms a pair with its neighbour Sextans A.

It might also be gravitationally associated with the galaxies NGC 3109 in Hydra constellation and the Antlia Dwarf in Antlia.