Canis Minor contains only two stars brighter than the fourthmagnitude,Procyon (Alpha Canis Minoris), with a magnitude of 0.34, andGomeisa (Beta Canis Minoris), with a magnitude of 2.9. The constellation's dimmer stars were noted byJohann Bayer, who named eight stars including Alpha and Beta, andJohn Flamsteed, who numbered fourteen. Procyon is theeighth-brightest star in the night sky, as well as one of theclosest. A yellow-whitemain-sequence star, it has awhite dwarfcompanion. Gomeisa is a blue-white main-sequence star.Luyten's Star is a ninth-magnitudered dwarf and theSolar System's next closest stellar neighbour in the constellation after Procyon. Additionally, Procyon and Luyten's Star are only 1.12 light-years away from each other,[2] and Procyon would be the brightest star in Luyten's Star's sky. The fourth-magnitudeHD 66141, which has evolved into an orangegiant towards the end of itslife cycle, was discovered to have a planet in 2012. There are two faintdeep-sky objects within the constellation's borders. The 11Canis-Minorids are ameteor shower that can be seen in early December.
Canis Minor, as depicted byJohann Bode in his 1801 workUranographia
Though strongly associated with theClassical Greekuranographic tradition, Canis Minor originates from ancientMesopotamia. Procyon and Gomeisa were calledMASH.TAB.BA or "twins" in theThree Stars Each tablets, dating to around 1100 BC. In the laterMUL.APIN, this name was also applied to the pairs ofPi3 andPi4 Orionis andZeta andXi Orionis. The meaning ofMASH.TAB.BA evolved as well, becoming the twin deitiesLulal andLatarak, who are on the opposite side of the sky fromPapsukkal, the True Shepherd of Heaven inBabylonian mythology. Canis Minor was also given the nameDAR.LUGAL, its position defined as "the star which stands behind it [Orion]", in theMUL.APIN; the constellation represents arooster. This name may have also referred to the constellationLepus.[3]DAR.LUGAL was also denotedDAR.MUŠEN andDAR.LUGAL.MUŠEN in Babylonia. Canis Minor was then calledtarlugallu inAkkadian astronomy.[4]
Canis Minor was one of the original 48 constellations formulated byPtolemy in his second-centuryAlmagest, in which it was defined as a specific pattern (asterism) of stars; Ptolemy identified only two stars and hence no depiction was possible.[5] TheAncient Greeks called the constellation προκυων/Procyon, "coming before the dog", transliterated intoLatin asAntecanis,Praecanis, or variations thereof, by Cicero and others. Roman writers also appended the descriptorsparvus,minor orminusculus ("small" or "lesser", for its faintness),septentrionalis ("northerly", for its position in relation to Canis Major),primus (rising "first") orsinister (rising to the "left") to its nameCanis.[5]InGreek mythology, Canis Minor was sometimes connected with theTeumessian Fox, a beast turned into stone with its hunter,Laelaps, byZeus, who placed them in heaven as Canis Major (Laelaps) and Canis Minor (Teumessian Fox).[6][7]Eratosthenes accompanied the Little Dog with Orion, whileHyginus linked the constellation withMaera, a dog owned byIcarius of Athens.[8][9] On discovering the latter's death, the dog and Icarius' daughterErigone took their lives and all three were placed in the sky—Erigone asVirgo and Icarius asBoötes.[9] As a reward for his faithfulness, the dog was placed along the "banks" of the Milky Way, which the ancients believed to be a heavenly river, where he would never suffer from thirst.[10]
Themedieval Arabic astronomers maintained the depiction of Canis Minor (al-Kalb al-Asghar inArabic) as a dog; in hisBook of the Fixed Stars,Abd al-Rahman al-Sufi included a diagram of the constellation with a canine figure superimposed.[11][12] There was one slight difference between the Ptolemaic vision of Canis Minor and the Arabic; al-Sufi claimsMirzam, now assigned toOrion, as part of both Canis Minor—the collar of the dog—and its modern home. The Arabic names for both Procyon and Gomeisa alluded to their proximity and resemblance to Sirius, though they were not direct translations of the Greek; Procyon was calledash-Shi'ra ash-Shamiya, the "Syrian Sirius" and Gomeisa was calledash-Shira al-Ghamisa, the Sirius with bleary eyes.[11] Among theMerazig ofTunisia, shepherds note six constellations that mark the passage of the dry, hot season. One of them, calledMerzem, includes the stars of Canis Minor and Canis Major and is the herald of two weeks of hot weather.[13]
The ancient Egyptians thought of this constellation asAnubis, the jackal god.[14]
Alternative names have been proposed:Johann Bayer in the early 17th century termed the constellationFovea "The Pit", andMorus "Sycamine Tree". Seventeenth-century German poet and authorPhilippus Caesius linked it to the dog of Tobias from theApocrypha.[5]Richard A. Proctor gave the constellation the nameFelis "the Cat" in 1870 (contrasting with Canis Major, which he had abbreviated toCanis "the Dog"),[5] explaining that he sought to shorten the constellation names to make them more manageable oncelestial charts.[15] Occasionally, Canis Minor is confused with Canis Major and given the nameCanis Orionis ("Orion's Dog").[16]
InChinese astronomy, the stars corresponding to Canis Minor lie in theVermilion Bird of the South (南方朱雀,Nán Fāng Zhū Què). Procyon, Gomeisa and Eta Canis Minoris form an asterism known as Nánhé, the Southern River.[9][17] With its counterpart, the Northern River Beihe (Castor andPollux), Nánhé was also associated with a gate or sentry. Along withZeta and8 Cancri,6 Canis Minoris and11 Canis Minoris formed the asterismShuiwei, which literally means "water level". Combined with additional stars inGemini, Shuiwei represented an official who managed floodwaters or a marker of the water level.[9] Neighboring Korea recognized four stars in Canis Minor as part of a different constellation, "the position of the water". This constellation was located in the Red Bird, the southern portion of the sky.[18]
Polynesian peoples often did not recognize Canis Minor as a constellation, but they saw Procyon as significant and often named it; in theTuamotu Archipelago it was known asHiro, meaning "twist as a thread of coconut fiber", andKopu-nui-o-Hiro ("great paunch of Hiro"), which was either a name for the modern figure of Canis Minor or an alternative name for Procyon. Other names includedVena (after agoddess), onMangaia andPuanga-hori (falsePuanga, the name forRigel), inNew Zealand. In theSociety Islands, Procyon was calledAna-tahua-vahine-o-toa-te-manava, literally "Aster the priestess of brave heart", figuratively the "pillar for elocution".[19][20] TheWardaman people of theNorthern Territory in Australia gave Procyon and Gomeisa the namesMagum andGurumana, describing them as humans who were transformed intogum trees inthe Dreaming. Although their skin had turned to bark, they were able to speak with a human voice by rustling their leaves.[21]
TheAztec calendar was related totheir cosmology. The stars of Canis Minor were incorporated along with some stars of Orion and Gemini into an asterism associated with the day called "Water".[22]
Lying directly south of Gemini's bright starsCastor andPollux,[23] Canis Minor is a small constellation bordered byMonoceros to the south, Gemini to the north,Cancer to the northeast, andHydra to the east. It does not borderCanis Major; Monoceros is in between the two. Covering 183 square degrees, Canis Minor ranks seventy-first of the 88 constellations in size. It appears prominently in the southern sky during theNorthern Hemisphere's winter.[24] The constellation boundaries, as set by Belgian astronomerEugène Delporte in 1930, are defined by a polygon of 14 sides. In theequatorial coordinate system, theright ascension coordinates of these borders lie between07h 06.4m and08h 11.4m, while thedeclination coordinates are between 13.22° and −0.36°.[1] Most visible in the evening sky from January to March,[25] Canis Minor is most prominent at 10 p.m. during mid-February.[26] It is then seen earlier in the evening until July, when it is only visible after sunset before setting itself, and rising in the morning sky before dawn.[27] The constellation's three-letter abbreviation, as adopted by theInternational Astronomical Union in 1922, is "CMi".[28]
The constellation Canis Minor as it can be seen by the naked eye
Canis Minor contains only two stars brighter than fourthmagnitude. At magnitude 0.34,[29] Procyon, or Alpha Canis Minoris, is theeighth-brightest star in the night sky, as well as one of theclosest. Its name means "before the dog" or "preceding the dog" in Greek, as it rises an hour before the "Dog Star",Sirius, of Canis Major. It is abinary star system, consisting of a yellow-whitemain-sequence star[30] ofspectral type F5 IV-V, named Procyon A, and a faintwhite dwarf companion of spectral type DA, named Procyon B. Procyon B, which orbits the more massive star every 41 years, is of magnitude 10.7.[30] Procyon A is 1.4 times theSun's mass, while its smaller companion is 0.6 times as massive as the Sun.[31] The system is 11.4light-years (3.5parsecs) fromEarth, the shortest distance to a northern-hemisphere star of the first magnitude.[30][32]Gomeisa, or Beta Canis Minoris, with a magnitude of 2.89, is the second-brightest star in Canis Minor. Lying 160 ± 10 light-years (49.1 ± 3.1 parsecs) from theSolar System,[33] it is a blue-white main-sequence star ofspectral class B8 Ve.[34] Although fainter to Earth observers, it is much brighter than Procyon, and is 250 times asluminous and three times as massive as the Sun.[35] Although its variations are slight, Gomeisa is classified as ashell star (Gamma Cassiopeiae variable), with a maximum magnitude of 2.84 and a minimum magnitude of 2.92.[34] It is surrounded by a disk of gas which it heats and causes to emit radiation.[35]
Johann Bayer used the Greek letters Alpha to Eta to label the most prominent eight stars in the constellation, designating two stars as Delta (named Delta1 and Delta2).[36]John Flamsteed numbered fourteen stars, discerning a third star he named Delta3;[37] his star 12 Canis Minoris was not found subsequently.[38] In Bayer's 1603 workUranometria, Procyon is located on the dog's belly, and Gomeisa on its neck.[39]Gamma,Epsilon andEta Canis Minoris lie nearby,[40] marking the dog's neck, crown and chest, respectively.[39] Although it has an apparent magnitude of 4.34, Gamma Canis Minoris is an orangeK-typegiant of spectral class K3-III C, which lies 318 light-years (97 parsecs) away.[41] Its colour is obvious when seen through binoculars.[40] It is a multiple system, consisting of thespectroscopic binary Gamma A and three optical companions, Gamma B, magnitude 13; Gamma C, magnitude 12; and Gamma D, magnitude 10. The two components of Gamma A orbit each other every 389.2 days, with an eccentric orbit that takes their separation between 2.3 and 1.4astronomical units (AU).[42] Epsilon Canis Minoris is a yellowbright giant of spectral class G6.5IIb of magnitude of 4.99.[43] It lies 730–810 light-years (220–250 parsecs) from Earth,[44] with 13 times the diameter and 750 times the luminosity of the Sun.[45] Eta Canis Minoris is a giant of spectral class F0III of magnitude 5.24,[46] which has a yellowish hue when viewed through binoculars as well as a faint companion of magnitude 11.1.[24][47] Located 4arcseconds from the primary, the companion star is actually around 440 AU from the main star and takes around 5,000 years to orbit it.[48]
Near Procyon, three stars share the nameDelta Canis Minoris.Delta1 is a yellow-whiteF-type giant of magnitude 5.25 located around 790 light-years (240 parsecs) from Earth. About 360 times as luminous and 3.75 times as massive as the Sun, it is expanding and cooling as it ages, having spent much of its life as amain sequence star of spectrum B6V.[48] Also known as 8 Canis Minoris,Delta2 is anF-type main-sequence star of spectral type F2V and magnitude 5.59 which is 136 light-years (42 parsecs) distant.[49] The last of the trio,Delta3 (also known as 9 Canis Minoris), is awhite main sequence star of spectral type A0Vnn and magnitude 5.83 which is 680 light-years (210 parsecs) distant.[50] These stars mark the paws of the Lesser Dog's left hind leg, while magnitude 5.13Zeta marks the right.[39][51] A blue-whitebright giant of spectral type B8II, Zeta lies around 623 light-years (191 parsecs) away from the Solar System.[51]
Lying 222 ± 7 light-years away with an apparent magnitude of 4.39,[52][53]HD 66141 is 6.8 billion years old and hasevolved into an orange giant of spectral type K2III with a diameter around 22 times that of the Sun, and weighing 1.1 solar masses. It is 174 times as luminous as the Sun, with anabsolute magnitude of −0.15.[54] HD 66141 was mistakenly named 13 Puppis, as its celestial coordinates were recorded incorrectly when catalogued and hence mistakenly thought to be in the constellation ofPuppis; Bode gave it the name Lambda Canis Minoris, which is now obsolete.[55] The orange giant is orbited by a planet,HD 66141b, which was detected in 2012 by measuring the star'sradial velocity. The planet has a mass around 6 times that ofJupiter and aperiod of 480 days.[53]
Ared giant of spectral type M4III,BC Canis Minoris lies around 500 light-years (150 parsecs) distant from the Solar System.[56] It is asemiregular variable star that varies between a maximum magnitude of 6.14 and minimum magnitude of 6.42.[57] Periods of 27.7, 143.3 and 208.3 days have been recorded in its pulsations.[56]AZ,AD andBI Canis Minoris areDelta Scuti variables—short period (six hours at most) pulsating stars that have been used asstandard candles and as subjects to studyastroseismology.[58] AZ is of spectral type A5IV,[59] and ranges between magnitudes 6.44 and 6.51 over a period of 2.3 hours.[60] AD has a spectral type of F2III,[61] and has a maximum magnitude of 9.21 and minimum of 9.51, with a period of approximately 2.95 hours.[62] BI is of spectral type F2 with an apparent magnitude varying around 9.19[63] and a period of approximately 2.91 hours.[64]
At least three red giants areMira variables in Canis Minor.S Canis Minoris, of spectral type M7e,[65] is the brightest, ranging from magnitude 6.6 to 13.2 over a period of 332.94 days.[24][66]V Canis Minoris ranges from magnitude 7.4 to 15.1 over a period of 366.1 days. Similar in magnitude isR Canis Minoris, which has a maximum of 7.3, but a significantly brighter minimum of 11.6. AnS-type star, it has a period of 337.8 days.[67]
YZ Canis Minoris is ared dwarf of spectral type M4.5V and magnitude 11.2,[68] roughly three times the size of Jupiter and 20 light-years (6.1 parsecs) from Earth. It is aflare star, emitting unpredictable outbursts of energy for mere minutes, which might be much more powerful analogues ofsolar flares.[69]Luyten's Star (GJ 273) is a red dwarf star of spectral type M3.5V and close neighbour of the Solar System. Its visual magnitude of 9.9 renders it too faint to be seen with the naked eye,[70] even though it is only 12.39 light-years (3.80 parsecs) away.[71] Fainter still isPSS 544-7, an eighteenth-magnitude red dwarf around 20 per cent the mass of the Sun, located 685 light-years (210 parsecs) from Earth. First noticed in 1991, it is thought to be a cannonball star, shot out of a star cluster and now moving rapidly through space directly away from thegalactic disc.[72]
TheWZ Sagittae-typedwarf novaDY Canis Minoris (also known asVSX J074727.6+065050) flared up to magnitude 11.4 over January and February 2008 before dropping eight magnitudes to around 19.5 over approximately 80 days. It is a remote binary star system where a white dwarf and low-mass star orbit each other close enough for the former star to draw material off the latter and form anaccretion disc. This material builds up until it erupts dramatically.[73]
TheMilky Way passes through much of Canis Minor, yet it has fewdeep-sky objects.[75]William Herschel recorded four objects in his 1786 workCatalogue of Nebulae and Clusters of Stars, including two he mistakenly believed were star clusters.[76]NGC 2459 is a group of five thirteenth- and fourteenth-magnitude stars that appear to lie close together in the sky but are not related.[77] A similar situation has occurred withNGC 2394, also in Canis Minor.[78] This is a collection of fifteen unrelated stars of ninth magnitude and fainter.[76]
Herschel also observed three faint galaxies, two of which are interacting with each other.[76]NGC 2508 is alenticular galaxy of thirteenth magnitude, estimated at 205 million light-years' distance (63 million parsecs) with a diameter of 80,000 light-years (25,000 parsecs).[79] Named as a single object by Herschel,NGC 2402 is actually a pair of near-adjacent galaxies that appear to be interacting with each other. Only of fourteenth and fifteenth magnitudes, respectively, the elliptical and spiral galaxy are thought to be approximately 245 million light-years distant, and each measure 55,000 light-years in diameter.[80]
The 11 Canis-Minorids, also called the Beta Canis Minorids,[81] are ameteor shower that arise near the fifth-magnitude star11 Canis Minoris and were discovered in 1964 by Keith Hindley, who investigated theirtrajectory and proposed a common origin with the cometD/1917 F1 Mellish.[82] However, this conclusion has been refuted subsequently as the number of orbits analysed was low and their trajectories too disparate to confirm a link.[83] They last from 4 to 15 December, peaking over 10 and 11 December.[84]
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