Theplane of theMilky Way passes through Pyxis. A faint constellation, its three brightest stars—Alpha,Beta andGamma Pyxidis—are in a rough line. At magnitude 3.68, Alpha is the constellation's brightest star. It is a blue-white star approximately 880light-years (270parsecs) distant and around 22,000 times asluminous as the Sun.
Pyxis is located close to the stars that formed the old constellationArgo Navis, the ship ofJason and theArgonauts. Parts of Argo Navis were the Carina (the keel or hull), the Puppis (the stern), and the Vela (the sails). These eventually became their own constellations. In the 19th century,John Herschel suggested renaming Pyxis to Malus (meaning themast) but the suggestion was not followed.
Pyxis is positioned just south of the starAlphard in the constellationHydra midway betweenVirgo andCancer. Although it is completely visible from latitudes south of53 degrees north, its best evening-sky visibility is during February and March in the southern hemisphere.
In ancientChinese astronomy, Alpha, Beta, and Gamma Pyxidis formed part ofTianmiao, a celestial temple honouring the ancestors of the emperor, along with stars from neighbouringAntlia.[4]
The French astronomerNicolas-Louis de Lacaille first described theconstellation in French asla Boussole (the Marine Compass) in 1752,[5][6] after he had observed and catalogued almost 10,000 southern stars during a two-year stay at theCape of Good Hope. He devised fourteen new constellations in uncharted regions of theSouthern Celestial Hemisphere not visible from Europe. All but one honoured instruments that symbolised theAge of Enlightenment.[b] Lacaille Latinised the name toPixis [sic]Nautica on his 1763 chart.[7] The Ancient Greeks identified the four main stars of Pyxis as the mast of the mythologicalJason's ship,Argo Navis.[8]
German astronomerJohann Bode defined the constellation Lochium Funis, the Log and Line—a nautical device once used for measuring speed and distance travelled at sea—around Pyxis in his 1801 star atlas, but the depiction did not survive.[9] In 1844John Herschel attempted to resurrect the classical configuration of Argo Navis by renaming it Malus the Mast, a suggestion followed byFrancis Baily, butBenjamin Gould restored Lacaille's nomenclature.[7] For instance,Alpha Pyxidis is referenced as α Mali in an old catalog of theUnited States Naval Observatory (star 3766, page 97).[10]
The constellation of Pyxis, the compass, as it can be seen by the naked eye
Covering 220.8 square degrees and hence 0.535% of the sky, Pyxis ranks 65th of the88 modern constellations by area.[11] Its position in theSouthern Celestial Hemisphere means that the whole constellation is visible to observers south of52°N.[11][c] It is most visible in the evening sky in February and March.[12] A small constellation, it is bordered byHydra to the north,Puppis to the west,Vela to the south, and Antlia to the east. The three-letter abbreviation for the constellation, as adopted by theInternational Astronomical Union in 1922, is "Pyx".[13] The official constellation boundaries, as set by Belgian astronomerEugène Delporte in 1930, are defined by apolygon of eight sides (illustrated in infobox). In theequatorial coordinate system, theright ascension coordinates of these borders lie between8h 27.7m and9h 27.6m, while thedeclination coordinates are between −17.41° and −37.29°.[14]
Lacaille gaveBayer designations to ten stars now named Alpha to Lambda Pyxidis, skipping the Greek letters iota and kappa. Although a nautical element, the constellation was not an integral part of the old Argo Navis and hence did not share in the original Bayer designations of that constellation, which were split between Carina, Vela and Puppis.[7] Pyxis is a faint constellation, its three brightest stars—Alpha,Beta andGamma Pyxidis—forming a rough line.[15] Overall, there are 41 stars within the constellation's borders withapparent magnitudes brighter than or equal to 6.5.[d][11]
With an apparent magnitude of 3.68, Alpha Pyxidis is the brightest star in the constellation.[17] Located 880 ± 30light-years distant from Earth,[18] it is a blue-whitegiant star of spectral type B1.5III that is around 22,000 times asluminous as theSun and has 9.4 ± 0.7 times its diameter. It began life with a mass 12.1 ± 0.6 times that of the Sun, almost 15 million years ago.[19] Its light is dimmed by 30% due tointerstellar dust, so would have a brighter magnitude of 3.31 if not for this.[17] The second brightest star at magnitude 3.97 is Beta Pyxidis, a yellowbright giant orsupergiant of spectral type G7Ib-II that is around 435 times as luminous as the Sun,[20] lying 420 ± 10 light-years distant away from Earth.[18] It has a companion star of magnitude 12.5 separated by 9arcseconds.[21] Gamma Pyxidis is a star of magnitude 4.02 that lies 207 ± 2 light-years distant.[18] It is an orange giant of spectral type K3III that has cooled and swollen to 3.7 times the diameter of the Sun after exhausting its core hydrogen.[22]
Kappa Pyxidis was catalogued but not given a Bayer designation by Lacaille, but Gould felt the star was bright enough to warrant a letter.[7] Kappa has a magnitude of 4.62 and is 560 ± 50 light-years distant.[18] An orange giant of spectral type K4/K5III,[23] Kappa has a luminosity approximately 965 times that of the Sun.[20] It is separated by 2.1 arcseconds from a magnitude 10 star.[24]Theta Pyxidis is ared giant of spectral type M1III and semi-regular variable with two measured periods of 13 and 98.3 days, and an average magnitude of 4.71,[25] and is 500 ± 30 light-years distant from Earth.[18] It has expanded to approximately 54 times the diameter of the Sun.[22]
Located around 4 degrees northeast of Alpha isT Pyxidis,[26] a binary star system composed of awhite dwarf with around 0.8 times the Sun's mass and ared dwarf that orbit each other every 1.8 hours. This system is located around 15,500 light-years away from Earth.[27] Arecurrent nova, it has brightened to the 7th magnitude in the years 1890, 1902, 1920, 1944, 1966 and 2011 from a baseline of around 14th magnitude. These outbursts are thought to be due to the white dwarf accreting material from its companion and ejecting periodically.[28]
TY Pyxidis is aneclipsing binary star whose apparent magnitude ranges from 6.85 to 7.5 over 3.2 days.[29] The two components are both of spectral type G5IV with a diameter 2.2 times,[30] and mass 1.2 times that of the Sun, and revolve around each other every 3.2 days.[31] The system is classified as aRS Canum Venaticorum variable, a binary system with prominentstarspot activity,[29] and lies 184 ± 5 light-years away.[18] The system emits X-rays, and analysing the emission curve over time led researchers to conclude that there was a loop of material arcing between the two stars.[32]RZ Pyxidis is another eclipsing binary system, made up of two young stars less than 200,000 years old. Both are hot blue-white stars of spectral type B7V and are around 2.5 times the size of the Sun. One is around five times as luminous as the Sun and the other around four times as luminous.[33] The system is classified as aBeta Lyrae variable, the apparent magnitude varying from 8.83 to 9.72 over 0.66 days.[34]XX Pyxidis is one of the more-studied members of a class of stars known asDelta Scuti variables[35]—short period (six hours at most) pulsating stars that have been used asstandard candles and as subjects to studyastroseismology.[36] Astronomers made more sense of its pulsations when it became clear that it is also a binary star system. The main star is a white main sequence star of spectral type A4V that is around 1.85 ± 0.05 times as massive as the Sun. Its companion is most likely a red dwarf of spectral type M3V, around 0.3 times as massive as the Sun. The two are very close—possibly only 3 times the diameter of the Sun between them—and orbit each other every 1.15 days. The brighter star is deformed into an egg shape.[35]
AK Pyxidis is a red giant of spectral type M5III and semi-regular variable that varies between magnitudes 6.09 and 6.51.[37] Its pulsations take place over multiple periods simultaneously of 55.5, 57.9, 86.7, 162.9 and 232.6 days.[25]UZ Pyxidis is another semi-regular variable red giant, this time acarbon star, that is around 3560 times as luminous as the Sun with a surface temperature of 3482 K, located 2116 light-years away from Earth.[20] It varies between magnitudes 6.99 and 7.83 over 159 days.[38]VY Pyxidis is aBL Herculis variable (type II Cepheid), ranging betweenapparent magnitudes 7.13 and 7.40 over a period of 1.24 days.[39] Located around 650 light-years distant, it shines with aluminosity approximately 45 times that of the Sun.[20]
The closest star to Earth in the constellation isGliese 318, a white dwarf of spectral class DA5 and magnitude 11.85.[40] Its distance has been calculated to be 26 light-years,[41] or 28.7 ± 0.5 light-years distant from Earth. It has around 45% of the Sun's mass, yet only 0.15% of its luminosity.[42]WISEPC J083641.12-185947.2 is abrown dwarf ofspectral type T8p located around 72 light-years from Earth. Discovered by infrared astronomy in 2011, it has a magnitude of 18.79.[43]
Pyxis is home to three stars with confirmed planetary systems—all discovered byDoppler spectroscopy. Ahot Jupiter,HD 73256 b, that orbitsHD 73256 every 2.55 days, was discovered using theCORALIE spectrograph in 2003. The host star is a yellow star of spectral type G9V that has 69% of our Sun's luminosity, 89% of its diameter and 105% of its mass. Around 119 light-years away, it shines with an apparent magnitude of 8.08 and is around a billion years old.[44]HD 73267 b was discovered with theHigh Accuracy Radial Velocity Planet Searcher (HARPS) in 2008. It orbitsHD 73267 every 1260 days, a 7 billion-year-old star of spectral type G5V that is around 89% as massive as the Sun.[45] Ared dwarf of spectral type M2.5V that has around 42% the Sun's mass,Gliese 317 is orbited by two gas giant planets. Around 50 light-years distant from Earth, it is a good candidate for future searches for more terrestrial rocky planets.[46]
The planetary nebula NGC 2818, imaged by the Hubble telescope
Pyxis lies in theplane of theMilky Way, although part of the eastern edge is dark, with material obscuring our galaxy arm there.NGC 2818 is aplanetary nebula that lies within a dimopen cluster of magnitude 8.2.[47]NGC 2818A is anopen cluster that lies on line of sight with it.[48]K 1-2 is a planetary nebula whose central star is aspectroscopic binary composed of two stars in close orbit withjets emanating from the system. The surface temperature of one component has been estimated at as high as 85,000 K.[49]NGC 2627 is anopen cluster of magnitude 8.4 that is visible in binoculars.[48]
Discovered in 1995,[3] thePyxis globular cluster is a 13.3 ± 1.3 billion year-oldglobular cluster situated around 130,000 light-years distant from Earth and around 133,000 light-years distant from the centre of the Milky Way—a region not previously thought to contain globular clusters.[50] Located in thegalactic halo, it was noted to lie on the same plane as theLarge Magellanic Cloud and the possibility has been raised that it might be an escaped object from that galaxy.[3]
NGC 2613 is a spiral galaxy of magnitude 10.5 which appears spindle-shaped as it is almost edge-on to observers on Earth.[51]Henize 2-10 is a dwarf galaxy which lies 30 million light-years away. It has a black hole of around a million solar masses at its centre. Known as astarburst galaxy due to very high rates of star formation, it has a bluish colour due to the huge numbers of young stars within it.[52]
^While parts of the constellation technically rise above the horizon to observers between the latitudes of 52°N and72°N, stars within a few degrees of the horizon are to all intents and purposes unobservable.[11]
^Objects of magnitude 6.5 are among the faintest visible to the unaided eye in suburban-rural transition night skies.[16]
^abcdeWagman, Morton (2003).Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others. Blacksburg, Virginia: The McDonald & Woodward Publishing Company. pp. 6–7,261–62.ISBN978-0-939923-78-6.
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^Templeton, Matthew (16 July 2010)."Delta Scuti and the Delta Scuti Variables".Variable Star of the Season. AAVSO (American Association of Variable Star Observers). Retrieved5 September 2015.
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^Kirkpatrick, J. Davy; Gelino, Christopher R.; Cushing, Michael C.; Mace, Gregory N.; Griffith, Roger L.; Skrutskie, Michael F.; Marsh, Kenneth A.; Wright, Edward L.; Eisenhardt, Peter R.; McLean, Ian S.; Mainzer, Amanda K.; Burgasser, Adam J.; Tinney, C. G.; Parker, Stephen; Salter, Graeme (2012). "Further Defining Spectral Type "Y" and Exploring the Low-mass End of the Field Brown Dwarf Mass Function".The Astrophysical Journal.753 (2): 156.arXiv:1205.2122.Bibcode:2012ApJ...753..156K.doi:10.1088/0004-637X/753/2/156.S2CID119279752.
^Anglada-Escude, Guillem; Boss, Alan P.; Weinberger, Alycia J.; Thompson, Ian B.; Butler, R. Paul; Vogt, Steven S.; Rivera, Eugenio J. (2012). "Astrometry and radial velocities of the planet host M dwarf Gliese 317: new trigonometric distance, metallicity and upper limit to the mass of Gliese 317 b".The Astrophysical Journal.764 (1): 37A.arXiv:1111.2623.Bibcode:2012ApJ...746...37A.doi:10.1088/0004-637X/746/1/37.S2CID118526264.
