Apus
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Apus is a small constellation in the southern sky. It represents a bird-of-paradise, and its name means "without feet" in Greek because the bird-of-paradise was once wrongly believed to lack feet. First depicted on a celestial globe by Petrus Plancius in 1598, it was charted on a star atlas by Johann Bayer in his 1603 Uranometria. The French explorer and astronomer Nicolas Louis de Lacaille charted and gave the brighter stars their Bayer designations in 1756.
The five brightest stars are all reddish in hue. Shading the others at apparent magnitude 3.8 is Alpha Apodis, an orange giant that has around 48 times the diameter and 928 times the luminosity of the Sun. Marginally fainter is Gamma Apodis, another aging giant star. Delta Apodis is a double star, the two components of which are 103 arcseconds apart and visible with the naked eye. Two star systems have been found to have planets.
HistoryEdit
Apus was one of twelve constellations published by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman who had sailed on the first Dutch trading expedition, known as the Eerste Schipvaart, to the East Indies. It first appeared on a 35-cm (14 in) diameter celestial globe published in 1598 in Amsterdam by Plancius with Jodocus Hondius.<ref name=ridpathbayer>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> De Houtman included it in his southern star catalogue in 1603 under the Dutch name De Paradijs Voghel, "The Bird of Paradise",<ref name="ley196312">Template:Cite magazine</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and Plancius called the constellation Paradysvogel Apis Indica; the first word is Dutch for "bird of paradise". Apis (Latin for "bee") is assumed to have been a typographical error for avis ("bird").Template:R<ref name="ridpath">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
After its introduction on Plancius's globe, the constellation's first known appearance in a celestial atlas was in German cartographer Johann Bayer's Uranometria of 1603.<ref name=ridpathbayer/> Bayer called it Apis Indica while fellow astronomers Johannes Kepler and his son-in-law Jakob Bartsch called it Apus or Avis Indica.<ref name=wagman>Template:Cite book</ref> The name Apus is derived from the Greek apous, meaning "without feet". This referred to the Western misconception that the bird-of-paradise had no feet, which arose because the only specimens available in the West had their feet and wings removed. Such specimens began to arrive in Europe in 1522, when the survivors of Ferdinand Magellan's expedition brought them home.<ref name="ridpath"/> The constellation later lost some of its tail when Nicolas-Louis de Lacaille used those stars to establish Octans in the 1750s.<ref name="ridpath"/>
CharacteristicsEdit
Covering 206.3 square degrees and hence 0.5002% of the sky, Apus ranks 67th of the 88 modern constellations by area.<ref name=tirionconst>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Its position in the Southern Celestial Hemisphere means that the whole constellation is visible to observers south of 7°N.<ref name=tirionconst/>Template:Efn It is bordered by Ara, Triangulum Australe and Circinus to the north, Musca and Chamaeleon to the west, Octans to the south, and Pavo to the east. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Aps".<ref name="pa30_469">Template:Cite journal</ref> The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930,Template:Efn are defined by a polygon of six segments (illustrated in infobox). In the equatorial coordinate system, the right ascension coordinates of these borders lie between Template:RA and Template:RA, while the declination coordinates are between −67.48° and −83.12°.<ref name="boundary" />
FeaturesEdit
StarsEdit
Template:See also Lacaille gave twelve stars Bayer designations, labelling them Alpha through to Kappa, including two stars next to each other as Delta and another two stars near each other as Kappa.<ref name=wagman/> Within the constellation's borders, there are 39 stars brighter than or equal to apparent magnitude 6.5.Template:Efn<ref name=tirionconst/> Beta, Gamma and Delta Apodis form a narrow triangle, with Alpha Apodis lying to the east.<ref>Template:Cite book</ref> The five brightest stars are all red-tinged, which is unusual among constellations.<ref name=arnold>Template:Cite book</ref>
Alpha Apodis is an orange giant of spectral type K3III located 430 ± 20 light-years away from Earth,<ref name=dr2>Template:Cite DR2</ref> with an apparent magnitude of 3.8.<ref name=ridpath01>Template:Cite book</ref> It spent much of its life as a blue-white (B-type) main sequence star before expanding, cooling and brightening as it used up its core hydrogen.<ref name=kaler>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It has swollen to 48 times the Sun's diameter,<ref name=aaa367_521>Template:Cite journal</ref> and shines with a luminosity approximately 928 times that of the Sun, with a surface temperature of 4312 K.<ref name=Mcdonald>Template:Cite journal</ref> Beta Apodis is an orange giant 149 ± 2 light-years away,<ref name=dr2/> with a magnitude of 4.2.<ref name=ridpath01/> It is around 1.84 times as massive as the Sun, with a surface temperature of 4677 K.<ref>Template:Cite journal</ref> Gamma Apodis is a yellow giant of spectral type G8III located 150 ± 4 light-years away,<ref name=dr2/> with a magnitude of 3.87. It is approximately 63 times as luminous the Sun, with a surface temperature of 5279 K.<ref name=Mcdonald/> Delta Apodis is a double star, the two components of which are 103 arcseconds apart and visible through binoculars.<ref>Template:Cite book</ref> Delta1 is a red giant star of spectral type M4III located 630 ± 30 light-years away.<ref name=dr2/> It is a semiregular variable that varies from magnitude +4.66 to +4.87,<ref name=AAVSOdel1>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> with pulsations of multiple periods of 68.0, 94.9 and 101.7 days.<ref name=tabur>Template:Cite journal</ref> Delta2 is an orange giant star of spectral type K3III,<ref>Template:Cite journal</ref> located 550 ± 10 light-years away,<ref name=dr2/> with a magnitude of 5.3. The separate components can be resolved with the naked eye.<ref name=ridpath01/>
The fifth-brightest star is Zeta Apodis at magnitude 4.8,<ref name=arnold/> a star that has swollen and cooled to become an orange giant of spectral type K1III, with a surface temperature of 4649 K and a luminosity 133 times that of the Sun.<ref name=Mcdonald/> It is 300 ± 4 light-years distant.<ref name=dr2/> Near Zeta is Iota Apodis, a binary star system 1,040 ± 60 light-years distant,<ref name=dr2/> that is composed of two blue-white main sequence stars that orbit each other every 59.32 years. Of spectral types B9V and B9.5 V, they are both over three times as massive as the Sun.<ref>Template:Cite journal</ref>
Eta Apodis is a white main sequence star located 140.8 ± 0.9 light-years distant.<ref name=dr2/> Of apparent magnitude 4.89, it is 1.77 times as massive, 15.5 times as luminous as the Sun and has 2.13 times its radius. Aged 250 ± 200 million years old, this star is emitting an excess of 24 μm infrared radiation, which may be caused by a debris disk of dust orbiting at a distance of more than 31 astronomical units from it.<ref name="apj698">Template:Cite journal</ref>
Theta Apodis is a cool red giant of spectral type M7 III located 350 ± 30 light-years distant.<ref name=dr2/> It shines with a luminosity approximately 3879 times that of the Sun and has a surface temperature of 3151 K.<ref name=Mcdonald/> A semiregular variable, it varies by 0.56 magnitudes with a period of 119 days<ref name=mnras355_2_601>Template:Cite journal</ref>—or approximately 4 months.<ref name=ridpath01/> It is losing mass at the rate of Template:Nowrap times the mass of the Sun per year through its stellar wind. Dusty material ejected from this star is interacting with the surrounding interstellar medium, forming a bow shock as the star moves through the galaxy.<ref name=aaa537_A35>Template:Cite journal See table 1, IRAS 14003-7633.</ref> NO Apodis is a red giant of spectral type M3III that varies between magnitudes 5.71 and 5.95.<ref name=AAVSONO>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Located 780 ± 20 light-years distant, it shines with a luminosity estimated at 2059 times that of the Sun and has a surface temperature of 3568 K.<ref name=Mcdonald/> S Apodis is a rare R Coronae Borealis variable, an extremely hydrogen-deficient supergiant thought to have arisen as the result of the merger of two white dwarfs; fewer than 100 have been discovered as of 2012. It has a baseline magnitude of 9.7.<ref name=tisserand>Template:Cite journal</ref> R Apodis is a star that was given a variable star designation, yet has turned out not to be variable. Of magnitude 5.3,<ref name=arnold/> it is another orange giant.
Two star systems have had exoplanets discovered by doppler spectroscopy, and the substellar companion of a third star system—the sunlike star HD 131664—has since been found to be a brown dwarf with a calculated mass of the companion to 23 times that of Jupiter (minimum of 18 and maximum of 49 Jovian masses).<ref name="ReffertQuirrenbach">Template:Cite journal</ref> HD 134606 is a yellow sunlike star of spectral type G6IV that has begun expanding and cooling off the main sequence.<ref name="Gray">Template:Cite journal</ref> Three planets orbit it with periods of 12, 59.5 and 459 days, successively larger as they are further away from the star.<ref>Template:Cite journal</ref> HD 137388 is another star—of spectral type K2IV—that is cooler than the Sun and has begun cooling off the main sequence.<ref name="Gray"/> Around 47% as luminous and 88% as massive as the Sun, with 85% of its diameter, it is thought to be around 7.4 ± 3.9 billion years old.<ref name=" Bonfanti 2015">Template:Cite journal</ref> It has a planet that is 79 times as massive as the Earth and orbits its sun every 330 days at an average distance of 0.89 astronomical units (AU).<ref name=HARPSXXX>Template:Cite journal</ref>
Deep-sky objectsEdit
The Milky Way covers much of the constellation's area.<ref name="Inglis04">Template:Cite book</ref> Of the deep-sky objects in Apus, there are two prominent globular clusters—NGC 6101 and IC 4499—and a large faint nebula that covers several degrees east of Beta and Gamma Apodis.<ref name=hartungs>Template:Cite book</ref> NGC 6101 is a globular cluster of apparent magnitude 9.2 located around 50,000 light-years distant from Earth,<ref name=imaging>Template:Cite book</ref> which is around 160 light-years across. Around 13 billion years old, it contains a high concentration of massive bright stars known as blue stragglers, thought to be the result of two stars merging.<ref name="O'Meara">Template:Cite book</ref> IC 4499 is a loose globular cluster in the medium-far galactic halo;<ref name=ferraro>Template:Cite journal</ref> its apparent magnitude is 10.6.<ref name=seds>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
The galaxies in the constellation are faint.<ref name=hartungs/> IC 4633 is a very faint spiral galaxy surrounded by a vast amount of Milky Way line-of-sight integrated flux nebulae—large faint clouds thought to be lit by large numbers of stars.<ref name=imaging/>
See alsoEdit
NotesEdit
ReferencesEdit
External linksEdit
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