Circinus is a small, 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 ...
in the
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, appears ...
, first defined in 1756 by the French astronomer
Nicolas-Louis de Lacaille
Abbé Nicolas-Louis de Lacaille (; 15 March 171321 March 1762), formerly sometimes spelled de la Caille, was a kingdom of France, French astronomer and geodesist who named 14 out of the IAU designated constellations, 88 constellations. From 1750 ...
. 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
compass
A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with No ...
, referring to the
drafting tool used for drawing circles (it should not be confused with
Pyxis
Pyxis is a small and faint constellation in the southern sky. Abbreviated from Pyxis Nautica, its name is Latin for a mariner's compass (contrasting with Circinus, which represents a draftsman's compasses). Pyxis was introduced by Nicolas-Louis ...
, a constellation that represents a
mariner's compass which points north). Its brightest star is
Alpha Circini, 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), ...
of 3.19. Slightly
variable, it is the brightest
rapidly oscillating Ap star Rapidly oscillating Ap stars (roAp stars) are a subtype of the Ap star class that exhibit short-timescale rapid photometric or radial velocity variations. The known periods range between 5 and 23 minutes. They lie in the δ Scuti instability stri ...
in the night sky.
AX Circini is a
Cepheid variable
A Cepheid variable () is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period (typically 1–100 days) and amplitude. Cepheids are important cosmi ...
visible with the unaided eye, and
BX Circini is a faint star thought to have been formed from the merger of two
white dwarf
A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
s. Two sun-like stars have planetary systems:
HD 134060 has two small planets, and
HD 129445 has a
Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...
-like planet.
Supernova
A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
SN 185
SN 185 was a transient astronomical event observed in the year AD 185, likely a supernova
A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolut ...
appeared in Circinus in 185 AD and was recorded by Chinese observers. Two
nova
A nova ( novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", Latin for "new") that slowly fades over weeks or months. All observed novae involve white ...
e have been observed more recently, in the 20th century.
The
Milky Way
The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
runs through the constellation, featuring prominent objects such as the
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 ...
NGC 5823 and the
planetary nebula
A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives.
The term "planetary nebula" is a misnomer because they are unrelated to planets. The ...
NGC 5315. Circinus hosts a notable
spiral galaxy
Spiral galaxies form a galaxy morphological classification, class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae'' , the
Circinus Galaxy, discovered in 1977; it is the closest
Seyfert galaxy
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasar host galaxies. They have quasar-like nuclei (very luminous sources of electromagnetic radiation that are outside of our own galaxy) with very high surface ...
to the Milky Way. The
Alpha Circinids (ACI), a
meteor shower
A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at ext ...
also discovered in 1977, radiate from this constellation.
History
In 1756, French astronomer
Nicolas-Louis de Lacaille
Abbé Nicolas-Louis de Lacaille (; 15 March 171321 March 1762), formerly sometimes spelled de la Caille, was a kingdom of France, French astronomer and geodesist who named 14 out of the IAU designated constellations, 88 constellations. From 1750 ...
introduced the
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 ...
of Circinus with the French name ''le Compas'', representing a pair of dividing
compass
A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with No ...
es, on a chart of the southern sky.
On that chart, Lacaille portrayed the constellations of
Norma Norma may refer to:
* Norma (given name), a given name (including a list of people with the name)
** Norma Lizbeth Ramos, a Mexican bullying victim
Astronomy
*Norma (constellation)
* 555 Norma, a minor asteroid
* Cygnus Arm or Norma Arm, a spiral ...
, Circinus, and
Triangulum Australe
Triangulum Australe is a small constellation in the far Southern Celestial Hemisphere. Its name is Latin for "the southern triangle", which distinguishes it from Triangulum in the northern sky and is derived from the Acute triangle, acute, almost ...
, respectively, as a set square and ruler, a compass, and a surveyor's level in a set of draughtsman's instruments.
Circinus was given its current name in 1763, when Lacaille published an updated sky map with Latin names for the constellations he introduced.
Characteristics
Bordered by
Centaurus
Centaurus () is a bright constellation in the southern sky. One of the 88 modern constellations by area, largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one ...
,
Musca
is a small constellation in the deep southern sky. It was one of 12 constellations created by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman, and it first appeared on a celestial globe in diameter p ...
,
Apus
Apus is a small constellation in the Southern Celestial Hemisphere, southern sky. It represents a bird-of-paradise, and its name means "without feet" in Greek language, Greek because the bird-of-paradise was once wrongly believed to lack feet. ...
, Triangulum Australe, Norma and
Lupus
Lupus, formally called systemic lupus erythematosus (SLE), is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body. Symptoms vary among people and may be mild to severe. Common ...
, Circinus lies adjacent to the
Alpha
Alpha (uppercase , lowercase ) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter ''aleph'' , whose name comes from the West Semitic word for ' ...
and
Beta Centauri
Beta Centauri is a triple star system in the southern constellation of Centaurus. It is officially called Hadar (). The Bayer designation of Beta Centauri is Latinised from β Centauri, and abbreviated Beta Cen or β Cen. The syst ...
stars. As it is at
declination
In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. The declination angle is measured north (positive) or ...
−50° to −70°, the whole constellation is only visible south of
latitude
In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...
30° N. The official constellation boundaries, as set by Belgian astronomer
Eugène Delporte
Eugene is a common male given name that comes from the Greek εὐγενής (''eugenēs''), "noble", literally "well-born", from εὖ (''eu''), "well" and γένος (''genos''), "race, stock, kin".polygon
In geometry, a polygon () is a plane figure made up of line segments connected to form a closed polygonal chain.
The segments of a closed polygonal chain are called its '' edges'' or ''sides''. The points where two edges meet are the polygon ...
of 14 segments. In the
equatorial coordinate system
The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of astronomical object, celestial objects. It may be implemented in spherical coordinate system, spherical or Cartesian coordinate system, rect ...
, the
right ascension
Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the equinox (celestial coordinates), March equinox to the (hour circle of the) point in questio ...
coordinates of these borders lie between and , and the declination coordinates are between −55.43° and −70.62°.
Circinus
culminates each year at 9 p.m. on 30 July. The recommended three-letter abbreviation for the constellation, as adopted by the
International Astronomical Union
The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...
in 1922, is "Cir".
Features
Stars
Circinus is a faint constellation, with only one star brighter than fourth magnitude.
Alpha Circini, a white
main sequence
In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
star 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), ...
of 3.19, is 54
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 away and 4° south of
Alpha Centauri
Alpha Centauri (, α Cen, or Alpha Cen) is a star system in the southern constellation of Centaurus (constellation), Centaurus. It consists of three stars: Rigil Kentaurus (), Toliman (), and Proxima Centauri (). Proxima Centauri ...
.
Not only the brightest star in the constellation, it is also the brightest example of a
rapidly oscillating Ap (RoAp) star in the night sky. It has the unusual
spectral type
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 the ...
A7 Vp SrCrEu, showing increased emissions of
strontium
Strontium is a chemical element; it has symbol Sr and atomic number 38. An alkaline earth metal, it is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is exposed to ...
,
chromium
Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal.
Chromium ...
and
europium
Europium is a chemical element; it has symbol Eu and atomic number 63. It is a silvery-white metal of the lanthanide series that reacts readily with air to form a dark oxide coating. Europium is the most chemically reactive, least dense, and soft ...
. Stars of this type have oddly localised
magnetic field
A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...
s and are slightly
variable.
Alpha Circini forms a
binary
Binary may refer to:
Science and technology Mathematics
* Binary number, a representation of numbers using only two values (0 and 1) for each digit
* Binary function, a function that takes two arguments
* Binary operation, a mathematical op ...
star system
A star system or stellar system is a small number of stars that orbit each other, bound by gravity, gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally calle ...
with an
orange dwarf
A K-type main-sequence star, also referred to as a K-type dwarf, or orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("r ...
companion of spectral type K5 and magnitude 8.5,
[ which with a separation of 5.7 ]arcsecond
A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...
s is only discernible with a telescope. The distance between the two stars is 260 AU and they take 2600 years to rotate around a common centre of gravity.[ The second brightest star is Beta Circini, a white main sequence star of spectral type A3Va and a magnitude of 4.07, about 100 light-years away.] It has around 1.8 times the diameter of the Sun.
Gamma Circini
Gamma Circini, Latinized from γ Circini, is a star system in the constellation Circinus. It was noted as a double star by Herschel in 1835, who estimated the separation as 1 arc second. It is visible to the naked eye with an appar ...
is a binary star 450 light-years away,[ whose components need a telescope of 150 mm to be seen, as they are only 0.8 arcseconds apart.][ The brighter component is a bluish ]Be star
Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer ...
of spectral type B5IV+ and magnitude 4.51, while the dimmer component is a yellow star of magnitude 5.5. They orbit each other every 180 years.[ Delta Circini is also a multiple star whose components have magnitudes of 5.1 and 13.4 and orbit around a common centre of gravity every 3.9 days. The brighter component is a close ]eclipsing binary
A binary star or binary star system is a Star system, system of two stars that are gravity, gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved ...
(specifically, a rotating ellipsoidal variable),[ with a minor dip of magnitude (0.1). Both are hot blue stars of spectral types O7III-V and O9.5V, respectively, and are estimated to have around 22 and 12 times the Sun's mass. Over 3600 light-years away,] this system would outshine Venus
Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...
at magnitude −4.8 if it were 32 light-years (10 parsec
The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...
s) distant.[ The two main components are separated by 50 arcseconds, resolvable to the naked eye for individuals with good vision and easily discernible with a telescope.][
Eta Circini is a yellow giant of spectral type G8III and magnitude 5.17, located around 276 light-years distant,] and Zeta Circini is a blue-white main sequence star of spectral type B3V and magnitude 6.09, located around 1273 light-years away.
493 variable stars have been recorded in Circinus, but most have a very small range or are quite dim. Three prominent examples are Theta Circini, T Circini
T, or t, is the twentieth letter of 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 d ...
, and AX Circini. Theta Circini is a B-class irregular variable, ranging in magnitude from 5.0 to 5.4.[ T Circini has a B-type spectrum, ranging in magnitude from 10.6 to 9.3 over a period of 3.298 days,] although it is actually an eclipsing binary system rather than a pulsating star. AX is a Cepheid variable
A Cepheid variable () is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period (typically 1–100 days) and amplitude. Cepheids are important cosmi ...
that varies between magnitudes 5.6 and 6.19 over 5.3 days. It is a yellow-white supergiant of spectral type F8II+, 1600 light-years away. BP Circini is another Cepheid variable
A Cepheid variable () is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period (typically 1–100 days) and amplitude. Cepheids are important cosmi ...
with an apparent magnitude ranging from 7.37 to 7.71 over 2.4 days. Both cepheids are spectroscopic binaries, with companions that are blue-white stars of spectral type B6 and 5 and 4.7 solar masses, respectively. BX Circini is a faint star that fluctuates between magnitudes 12.57 and 12.62 over a period of 2 hours 33 minutes. Over 99% of its composition appears to be helium. Its origin is unclear, but thought to be the result of the merger of a helium and a carbon/oxygen white dwarf.
Several stars with planetary systems lie within the borders of Circinus, although none of the host stars are particularly prominent. HD 134060 is a sun-like yellow dwarf star of spectral type G0VFe+0.4 and magnitude 6.29, around 79 light-years away. Its two planets were discovered in 2011 through the radial velocity method
Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in th ...
: the smaller, HD 134060 b, has a mass of 0.0351 MJ (Jupiter masses) and orbits its star every 3.27 days, at 0.0444 AU; the larger, HD 134060 c (0.15 MJ), orbits farther out at 2.226 AU, with a period of approximately 1161 days. Even fainter, at magnitude 8.8, HD 129445 is 220 light-years away and has 99% of the Sun's mass and a similar spectral type of G8V. HD 129445 b, a Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...
-like planet (1.6 MJ) discovered in 2010 via the radial velocity method, orbits this star at a distance of 2.9 AU, approximately every 1840 days.
As this constellation intersects the plane of the Milky Way, there are many massive stars located in this constellation, including GKF2010 MN18 (or simply MN18), a blue supergiant located in a bipolar nebula, as well as 9 Wolf-Rayet stars, a very high number for such a small constellation.
Deep-sky objects
Three 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 ...
s and a planetary nebulae
A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionization, ionized gas ejected from red giant stars late in their lives.
The term "planetary nebula" is a misnomer because they are unrelated to pla ...
are found within the borders of Circinus, all visible with amateur telescopes of varying sizes. NGC 5823, also called Caldwell
Caldwell may refer to:
People
* Caldwell (surname)
* Caldwell (given name)
* Caldwell First Nation, a federally recognized First Nation in southern Ontario, Canada
Places
Great Britain
* Caldwell, Derbyshire, a hamlet
* Caldwell, Ea ...
88,[ is an 800-million-year-old open cluster, located 3500 light-years away and spanning a 12-light-year region along the constellation's northern border.] Despite having an integrated magnitude of 7.9,[ the cluster can be seen by ]star hopping
Star hopping is a technique that amateur astronomers often use to locate astronomical objects in the night sky. It can be used instead of or in addition to setting circles or go-to/push-to systems.
The problem
Many celestial objects of interes ...
from Beta Circini or from Alpha Centauri. It contains 80–100 stars of 10th magnitude and fainter, which are spread out over a diameter of 10 arcseconds. The brighter stars, however, are not true members of the cluster, as they are closer to the Earth than the dimmer ones. NGC 5823 appears distinct to the observer, sometimes seen as a reversed "S", as described by John Herschel
Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor and experimental photographer who invented the blueprint and did botanical work. ...
, although it has also been described as "tulip-shaped" and "boxy". That cluster can be easily mistaken with a similar cluster, NGC 5822, nearby in Lupus
Lupus, formally called systemic lupus erythematosus (SLE), is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body. Symptoms vary among people and may be mild to severe. Common ...
. Comparatively, open cluster NGC 5715 is fainter (integrated magnitude of 9.8)—its brightest star is only 11th magnitude—and smaller (7.0 arcminutes), comprising only 30 stars. The third open cluster, Pismis 20, contains 12 stars in a diameter of 4.5 arcseconds but exhibits a magnitude similar to NGC 5823 (7.8). At 8270 light-years, it requires an amateur telescope with an aperture over 300 mm to be easily discerned.
The planetary nebula NGC 5315 has a magnitude of 9.8 around a central star of magnitude 14.2, located 5.2 degrees west-southwest of Alpha Circini. It is only visible as a disc at magnifications over 200-fold. Bernes 145 is a dark
Darkness is the condition resulting from a lack of illumination, or an absence of visible light.
Human vision is unable to distinguish colors in conditions of very low luminance because the hue-sensitive photoreceptor cells on the retina are ...
and reflection nebula
In astronomy, reflection nebulae are interstellar cloud, clouds of Cosmic dust, interstellar dust which might reflect the light of a nearby star or stars. The energy from the nearby stars is insufficient to Ionization, ionize the gas of the nebu ...
first listed in the 1971 Bernes Catalog. The dark nebula component is easily visible in a large amateur telescope, and it measures 12 by 5 arcminutes. The smaller reflection nebula component requires a larger instrument and averted vision
Averted vision is a technique for viewing faint objects which uses peripheral vision. It involves not looking directly at the object, but looking a little off to the side, while continuing to concentrate on the object. This subject is discussed in ...
to be seen.
Circinus also houses ESO 97-G13, commonly known as the Circinus Galaxy. Discovered in 1977, it is a relatively unobscured galaxy (magnitude 10.6), which is unusual for galaxies located in constellations near the Milky Way
The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
, since their dim light is obscured by gas and dust. This oblong spiral galaxy
Spiral galaxies form a galaxy morphological classification, class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae'' with 6.9 by 3.0 arcminutes and 26,000 light-years in diameter, is located 13 million light-years away from Earth and lies 4 degrees off the galactic plane
The galactic plane is the plane (geometry), plane on which the majority of a disk-shaped galaxy's mass lies. The directions perpendicular to the galactic plane point to the galactic poles. In actual usage, the terms ''galactic plane'' and ''galac ...
. It is the closest Seyfert galaxy
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasar host galaxies. They have quasar-like nuclei (very luminous sources of electromagnetic radiation that are outside of our own galaxy) with very high surface ...
to the Milky Way, and therefore hosts an active galactic nucleus
An active galactic nucleus (AGN) is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. Such e ...
.
Circinus X-1
Circinus X-1 is an X-ray binary star system that includes a neutron star. Observation of Circinus X-1 in July 2007 revealed the presence of X-ray jets normally found in black hole systems; it is the first of the sort to be discovered tha ...
is an X-ray binary
X-ray binaries are a class of binary stars that are luminous in X-rays.
The X-rays are produced by matter falling from one component, called the ''donor'' (usually a relatively common main sequence star), to the other component, called the ''acc ...
star system that includes a neutron star
A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...
. Observations of Circinus X-1 in July 2007 revealed the presence of X-ray jets normally found in black hole
A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...
systems. Located at 19,000 light-years, the pulsar PSR B1509-58, also called the Circinus Pulsar, has expelled a 20-light-year-long jet of material from its southern pole, clearly visible in the X-ray
An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
spectrum. Another supernova remnant
A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar mat ...
in Circinus is that of SN 185
SN 185 was a transient astronomical event observed in the year AD 185, likely a supernova
A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolut ...
. Recorded by Chinese observers in 185 AD, SN 185 was visible in the night sky for around eight months; its remnants, known as RCW 86, cover an area larger than the typical full moon.
A white dwarf star in a close binary system can accumulate material from its companion until it ignites and blows off in a thermonuclear explosion, known as a nova
A nova ( novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", Latin for "new") that slowly fades over weeks or months. All observed novae involve white ...
.[ These stars generally brighten by 7 to 16 magnitudes. Nova Circini 1926, also known as X Circini, was observed at magnitude 6.5 on 3 September 1926, before fading and fluctuating between magnitudes 11.7 and 12.5, during 1928, and magnitude 13, in 1929. Nova Circini 1995 ( BY Circini) reached a maximum apparent magnitude of 7.2 in January 1995.] BW Circini
BW or Bw may stand for:
Businesses and organizations
* Baldwin Wallace University, Berea, Ohio, US
* Bergesen Worldwide, a shipping company
* Best Western, a hotel company
* British Waterways
* Brush Engineered Materials (NYSE stock symbol BW)
* ...
is a low mass X-ray binary system, comprising a black hole of around 8 solar masses and a yellow G0III-G5III subgiant star. X-ray outbursts were recorded in 1987 and 1997, and possibly 1971–72.
Meteor showers
Circinus is the radiant of an annual meteor shower
A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at ext ...
, the Alpha Circinids (ACI). First observed in Queensland
Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...
in 1977, the meteors have an average velocity of 27.1 km/s and are thought to be associated with a long-period comet
A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or coma surrounding the nucleus, and ...
.[ In 2011, ]Peter Jenniskens
Petrus Matheus Marie (Peter) Jenniskens (born 1962 in Meterik) is a Dutch- American astronomer and a senior research scientist at the Carl Sagan Center of the SETI Institute and at NASA Ames Research Center. He is an expert on meteor showers, a ...
proposed that the debris trail of comet C/1969 T1 could intersect with the Earth's orbit and generate a meteor outburst coming from a radiant close to Beta Circini. The ACI shower peaks on 4 June, the day it was first observed.
See also
* Circinus (Chinese astronomy)
References
External links
The Deep Photographic Guide to the Constellations: Circinus
{{DEFAULTSORT:Circinus
Southern constellations
Constellations listed by Lacaille