Visible at latitudes between +90° and −40°. Best visible at 21:00 (9 p.m.) during the month of August. [2]
Lyra (Latin for 'lyre', fromAncient Greek:λύρα; pronounced:/ˈlaɪrə/LY-rə)[3] is a smallconstellation. It is one of the 48 listed by the 2nd century astronomerPtolemy, and is one of the modern 88 constellations recognized by theInternational Astronomical Union. Lyra was often represented on star maps as avulture or aneagle carrying a lyre, and hence is sometimes referred to asVultur Cadens orAquila Cadens ("Falling Vulture"[4] or "Falling Eagle"), respectively. Beginning at the north, Lyra is bordered byDraco,Hercules,Vulpecula, andCygnus. Lyra is nearly overhead in temperate northern latitudes shortly after midnight at the start of summer. From the equator to about the40th parallel south it is visible low in the northern sky during the same (thus winter) months.
Lyra can be seen on the right of this c. 1825 star map fromUrania's Mirror.
InGreek mythology, Lyra represents thelyre ofOrpheus. Orpheus's music was said to be so great that even inanimate objects such asrocks could be charmed. JoiningJason and theArgonauts, his music was able to quell the voices of the dangerousSirens, who sang tempting songs to the Argonauts.[5]
At one point, Orpheus marriedEurydice, anymph. While fleeing from an attack byAristaeus, she stepped on a snake that bit her, killing her. To reclaim her, Orpheus entered theUnderworld, where the music from his lyre charmedHades, the god of the Underworld. Hades relented and let Orpheus bring Eurydice back, on the condition that he never once look back until outside. Unfortunately, near the very end, Orpheus faltered and looked back, causing Eurydice to be left in the Underworld forever. Orpheus spent the rest of his life strumming his lyre while wandering aimlessly through the land, rejecting all marriage offers from women.[5]
There are two main competing myths relating to the death of Orpheus. According toEratosthenes, Orpheus failed to make a necessary sacrifice toDionysus due to his regard forApollo as the supreme deity instead. Dionysus then sent his followers to rip Orpheus apart.Ovid tells a rather different story, saying that women, in retribution for Orpheus's rejection of marriage offers, ganged up and threw stones andspears. At first, his music charmed them as well, but eventually their numbers and clamor overwhelmed his music and he was hit by the spears. Both myths then state that his lyre was placed in the sky byZeus and Orpheus's bones were buried by themuses.[5] In a third myth, he was killed by the Thracian women because he looked on the rites ofFather Liber (Dionysus).[6]
The Roman bookDe astronomia, attributed toHyginus, also records another myth about Lyra, which said that it belonged toTheseus "for he was skilful in all the arts and seems to have learned the lyre as well". The book reports that the neighbouring constellation now known asHercules was said to depict many different mythical figures, including Theseus, Orpheus, or the musicianThamyris.[6] The proximity of these two constellations andCorona Borealis (perhaps a symbol of Theseus' royalty) could indicate that the three constellations were invented as a group.[7]
Vega and its surrounding stars are also treated as a constellation in other cultures. The area corresponding to Lyra was seen by the Arabs as avulture or aneagle diving with folded wings.[5] InWales, Lyra is known as King Arthur's Harp (Talyn Arthur), and King David's harp. The PersianHafiz called it the Lyre of Zurah.It has been called the Manger of the Infant Saviour, Praesepe Salvatoris.[8] In AustralianAboriginal astronomy, Lyra is known by theBoorong people inVictoria as theMalleefowl constellation.[9] Lyra was known asUrcuchillay by theIncas and was worshipped as an animal deity.[10][11]
Lyra is bordered by Vulpecula to the south, Hercules to the west, Draco to the north, and Cygnus to the east. Covering 286.5square degrees, it ranks 52nd of the88 modern constellations in size. It appears prominently in the northern sky during the Northern Hemisphere's summer, and the whole constellation is visible for at least part of the year to observers north of latitude 42°S.[12][n 2] Its mainasterism consists of six stars,[n 3] and 73 stars in total are brighter than magnitude 6.5.[12] The constellation's boundaries, as set by Belgian astronomerEugène Delporte in 1930, are defined by a 17-sided polygon. In theequatorial coordinate system, theright ascension coordinates of these borders lie between18h 14m and19h 28m, while thedeclination coordinates are between +25.66° and +47.71°.[13] TheInternational Astronomical Union (IAU) adopted the three-letter abbreviation "Lyr" for the constellation in 1922.[14]
The constellation Lyra, enhanced for color and contrast. Brightest five stars are labeled.
German cartographerJohann Bayer used the Greek lettersalpha throughnu to label the most prominent stars in the constellation. English astronomerJohn Flamsteed observed and labelled two stars each asdelta,epsilon,zeta and nu. He addedpi andrho, not usingxi andomicron as Bayer used these letters to denote Cygnus and Hercules on his map.[15]
The brightest star in the constellation is Vega (Alpha Lyrae), amain-sequence star ofspectral type A0Va.[16] Only 7.7 parsecs distant,[17] Vega is aDelta Scuti variable, varying betweenmagnitudes −0.02 and 0.07 over 0.2 days.[18] On average, it is the second-brightest star of the northern hemisphere (afterArcturus) and the fifth-brightest star in all, surpassed only by Arcturus,Alpha Centauri,Canopus, andSirius. Vega was thepole star in the year 12,000 BCE, and will again become the pole star around 14,000 CE.[19][20]
Vega is one of the most magnificent of all stars, and has been called "arguably the next most important star in the sky after theSun".[21] Vega was the first star other than the Sun to bephotographed,[22] as well as the first to have a clearspectrum recorded, showingabsorption lines for the first time.[23] The star was the first single main-sequence star other than the Sun to be known to emitX-rays,[24] and is surrounded by a circumstellardebris disk, similar to theKuiper Belt.[25] Vega forms one corner of the famousSummer Triangle asterism; along withAltair andDeneb, these three stars form a prominent triangle during the northern hemisphere summer.[26]
Vega also forms one vertex of a much smaller triangle, along with Epsilon andZeta Lyrae. Zeta forms a widebinary star visible in binoculars, consisting of anAm star and anF-typesubgiant. The Am star has an additional close companion, bringing the total number of stars in the system to three.[27] Epsilon is a more famous wide binary that can even be separated by thenaked eye under excellent conditions.[28] Both components are themselves close binaries which can be seen with telescopes to consist ofA- and F-type stars, and a faint star was recently found to orbit component C as well, for a total of five stars.[27]
South of Delta is Sulafat (Gamma Lyrae), ablue giant and the second-brightest star in the constellation. Around 190 parsecs distant,[17] it has been referred to as a "superficially normal" star.[32]
The final star forming the lyre's figure is Sheliak (Beta Lyrae), also a binary composed of a blue bright giant and an early B-type star.[33][34][35] In this case, the stars are so close together that the larger giant is overflowing itsRoche lobe and transferring material to the secondary, forming asemidetached system. The secondary, originally the less massive of the two, has accreted so much mass that it is now substantially more massive, albeit smaller, than the primary, and is surrounded by a thickaccretion disk.[36] The plane of the orbit is aligned with Earth and the system thus showseclipses, dropping nearly a full magnitude from its 3rd-magnitude baseline every 13 days,[37] although its period is increasing by around 19 seconds per year.[38] It is the prototype of theBeta Lyrae variables, eclipsing semidetached binaries of early spectral types in which there are no exact onsets of eclipses, but rather continuous changes in brightness.[39]
A long-exposure image of Lyra
Another easy-to-spot variable is the brightR Lyrae, north of the main asterism. Also known as 13 Lyrae, it is a 4th-magnitudered giant semiregular variable that varies by several tenths of a magnitude.[40] Its periodicity is complex, with several different periods of varying lengths, most notably one of 46 days and one of 64 days.[41] Even further north isFL Lyrae, a much fainter 9th-magnitudeAlgol variable that drops by half a magnitude every 2.18 days during the primary eclipse. Both components are main-sequence stars, the primary being late F-type and the secondary lateG-type. The system was one of the first main-sequence eclipsing binaries containing G-type star to have its properties known as well as the better-studied early-type eclipsing binaries.[42]
At the very northernmost edge of the constellation is the even fainterV361 Lyrae, an eclipsing binary that does not easily fall into one of the traditional classes, with features of Beta Lyrae,W Ursae Majoris, andcataclysmic variables.[43][44] It may be a representative of a very brief phase in which the system is transitioning into acontact binary.[45] It can be found less than a degree away from the naked-eye star16 Lyrae, a 5th-magnitudeA-type subgiant[46] located around 37 parsecs distant.[17]
The brightest star not included in the asterism and the westernmost cataloged by Bayer or Flamsteed isKappa Lyrae, a typical red giant[47] around 73 parsecs distant.[17] Similar bright orange or red giants include the 4th-magnitudeTheta Lyrae,[48]Lambda Lyrae,[49] andHD 173780.[47] Lambda is located just south of Gamma, Theta is positioned in the east, and HD 173780, the brightest star in the constellation with no Bayer or Flamsteed designation, is more southernly. Just north of Theta and of almost exactly the same magnitude isEta Lyrae, a blue subgiant with a near-solar metal abundance.[50] Also nearby is the faintHP Lyrae, apost-asymptotic giant branch (AGB) star that shows variability. The reason for its variability is still a mystery: first cataloged as an eclipsing binary, it was theorized to be anRV Tauri variable in 2002, but if so, it would be by far the hottest such variable discovered.[51]
In the extreme east isRR Lyrae, the prototype of the large class of variables known asRR Lyrae variables, which are pulsating variables similar toCepheids, but are evolvedpopulation II stars of spectral types A and F. Such stars are usually not found in a galaxy'sthin disk, but rather in thegalactic halo. Such stars serve asstandard candles, and thus are a reliable way to calculate distances to the globular clusters in which they reside.[39] RR Lyrae itself varies between magnitudes 7 and 8 while exhibiting theBlazhko effect.[52] The easternmost star designated byFlamsteed,19 Lyrae, is also a small-amplitude variable, anAlpha2 Canum Venaticorum variable with a period of just over one day.[53]
Another evolved star is the naked-eye variableXY Lyrae, a red bright giant[47] just north of Vega that varies between 6th and 7th magnitudes over a period of 120 days.[54] Also just visible to the naked eye is the peculiarclassical CepheidV473 Lyrae. It is unique in that it is the only known Cepheid in theMilky Way to undergo periodic phase and amplitude changes, analogous to the Blazhko effect in RR Lyrae stars.[55] At 1.5 days, its period was the shortest known for a classical Cepheid at the time of its discovery.[56]W andS Lyrae are two of the manyMira variables in Lyra. W varies between 7th and 12th magnitudes over approximately 200 days,[57] while S, slightly fainter, is a silicatecarbon star, likely of theJ-type.[58] Another evolved star isEP Lyrae, a faint RV Tauri variable and an "extreme example" of a post-AGB star. It and a likely companion are surrounded by a circumstellar disk of material.[59]
Rather close to Earth at a distance of only 16 parsecs (52 ly) isGliese 758. The sunlike primary star has abrown dwarf companion, the coldest to have been imaged around a sunlike star in thermal light when it was discovered in 2009.[60] Only slightly farther away isV478 Lyrae, an eclipsing[61]RS Canum Venaticorum variable whose primary star shows activestarspot activity.[62]
One of the most peculiar systems in Lyra isMV Lyrae, anova-like star consisting of ared dwarf and awhite dwarf.[63] Originally classified as aVY Sculptoris star due to spending most time at maximum brightness, since around 1979 the system has been dominantly at minimum brightness, with periodic outbursts.[64] Its nature is still not fully understood.[65] Another outbursting star isAY Lyrae, anSU Ursae Majoris-typedwarf nova that has undergone severalsuperoutbursts.[66] Of the same type isV344 Lyrae, notable for an extremely short period between superoutbursts coupled with one of the highest amplitudes for such a period.[67] The truenovaHR Lyrae flared in 1919 to a maximum magnitude of 6.5, over 9.5 magnitudes higher than in quiescence. Some of its characteristics are similar to those ofrecurring novae.[68]
Messier 56 is composed of a large number of stars, tightly bound to each other by gravity.[69] In Lyra are the objects M56, M57, and Kuiper 90.M56 is a rather looseglobular cluster at a distance of approximately 32,900light-years, with a diameter of about 85 light-years. Its apparent brightness is 8.3m.
M57, also known as the "Ring Nebula" and NGC 6720,[70] at a distance of 2,550 light-years from Earth is one of the best knownplanetary nebulae and the second to be discovered; its integrated magnitude is 8.8.[71] It was discovered in 1779 byAntoine Darquier, 15 years afterCharles Messier discovered theDumbbell Nebula.[72] Astronomers have determined that it is between 6,000 and 8,000 years old;[71] it is approximately one light-year in diameter.[73] The outer part of the nebula appears red in photographs because of emission fromionized hydrogen. The middle region is colored green;doubly ionized oxygen emits greenish-blue light. The hottest region, closest to the central star, appears blue because of emission fromhelium. The central star itself is awhite dwarf with a temperature of 120,000kelvins. In telescopes, the nebula appears as a visible ring with a green tinge; it is slightly elliptical because its three-dimensional shape is atorus orcylinder seen from a slight angle.[71] It can be found halfway betweenGamma Lyrae and Beta Lyrae.[73]
Another planetary nebula in Lyra isAbell 46. The central star,V477 Lyrae, is an eclipsingpost-common-envelope binary, consisting of a white dwarf primary and an oversized secondary component due to recent accretion. The nebula itself is of relatively low surface brightness compared to the central star,[74] and is undersized for the primary's mass for reasons not yet fully understood.[75]
NGC 6791 is a cluster of stars in Lyra. It contains three age groups of stars: 4 billion year-old white dwarfs, 6 billion year-old white dwarfs and 8 billion year-old normal stars.[76]
NGC 6745 is an irregularspiral galaxy in Lyra that is at a distance of 208 million light-years. Several million years ago, itcollided with a smaller galaxy, which created a region filled with young, hot, blue stars. Astronomers do not know if the collision was simply a glancing blow or a prelude to a full-on merger, which would end with the two galaxies incorporated into one larger, probablyelliptical galaxy.[71]
A remarkable long-durationgamma-ray burst wasGRB 050525A, which flared in 2005. Theafterglow re-brightened at 33 minutes after the original burst, only the third found to exhibit such an effect in the timeframe,[77] and unable to be completely explained by known phenomena.[78] The light curve observed over the next 100 days was consistent with that of asupernova or even ahypernova, dubbedSN 2005nc.[79] The host galaxy proved elusive to find at first,[80] although it was subsequently identified.[81]
In orbit around the orange subgiant starHD 177830 is one of the earliestexoplanets to be detected. A jovian-mass planet, it orbits in an eccentric orbit with a period of 390 days.[82] A second planet closer to the star was discovered in 2011.[83] Visible to the naked eye areHD 173416, ayellow giant hosting a planet over twice the mass of Jupiter discovered in 2009;[84] andHD 176051, a low-mass binary star containing another high-mass planet.[85] Just short of naked-eye visibility isHD 178911, a triple system consisting of a close binary and a visually separable sunlike star. The sunlike star has a planet with over 6 Jupiter masses discovered in 2001, the second found in a triple system after that of16 Cygni.[86]
One of the most-studied exoplanets in the night sky isTrES-1b, in orbit around the starGSC 02652-01324. Detected from atransit of its parent star, the planet has around 3/4 the mass of Jupiter, yet orbits its parent star in only three days.[87] The transits have been reported to have anomalies multiple times. Originally thought to be possibly due to the presence of an Earth-like planet, it is now accepted that the irregularities are due to a large starspot.[88] Also discovered by the transit method isWASP-3b, with 1.75 times the mass of Jupiter. At the time of its discovery, it was one of the hottest known exoplanets, in orbit around theF-type main-sequence starWASP-3.[89] Similar to TrES-1b, irregularities in the transits had left open the possibility of a second planet, although this now appears unlikely as well.[90]
Lyra is one of three constellations (along with neighboring Cygnus and Draco) to be in theKepler Mission's field of view, and as such it contains many more known exoplanets than most constellations. One of the first discovered by the mission isKepler-7b, an extremely low-density exoplanet with less than half the mass of Jupiter, yet nearly 1.5 times the radius.[91] Almost as sparse isKepler-8b, only slightly more massive and of a similar radius.[92] TheKepler-20 system contains five known planets; three of them are only slightly smaller thanNeptune,[93] while the other two are some of the firstEarth-sized exoplanets to be discovered.[94]Kepler-37 is another star with an exoplanet discovered by Kepler; the planet is the smallest knownextrasolar planet known as of February 2013.
In April 2013, it was announced that of the five planets orbitingKepler-62, at least two—Kepler-62e andKepler-62f—are within the boundaries of thehabitable zone of that star, where scientists think liquid water could exist, and are both candidates for being a solid, rocky, earth-like planet.[95][96] Theexoplanets are 1.6 and 1.4 times the diameter ofEarth respectively,[95] with their starKepler-62 at a distance of 1,200 light-years.[97]
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