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Sagitta is a dim but distinctive
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 northern sky. 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 'arrow', not to be confused with the significantly larger constellation Sagittarius 'the archer'. It was included among the 48 constellations listed by the 2nd-century astronomer
Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...
, and it remains one of the
88 modern constellations In contemporary astronomy, 88 constellations are recognized by the International Astronomical Union (IAU). Each constellation is a region of the sky bordered by arcs of right ascension and declination, together covering the entire celestial sph ...
defined 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 ...
. Although it dates to antiquity, Sagitta has no star brighter than 3rd
magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...
and has the third-smallest area of any constellation.
Gamma Sagittae Gamma Sagittae, Latinized from γ Sagittae, is the brightest star in northern constellation of Sagitta. A single star, it is visible to the naked eye with an apparent visual magnitude of +3.47. Based upon an annual parallax sh ...
is the constellation's brightest star, with an apparent magnitude of 3.47. It is an aging
red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...
star 90% as massive as the Sun that has cooled and expanded to a radius 54 times greater than it.
Delta Delta commonly refers to: * Delta (letter) (Δ or δ), the fourth letter of the Greek alphabet * D (NATO phonetic alphabet: "Delta"), the fourth letter in the Latin alphabet * River delta, at a river mouth * Delta Air Lines, a major US carrier ...
,
Epsilon Epsilon (, ; uppercase , lowercase or ; ) is the fifth letter of the Greek alphabet, corresponding phonetically to a mid front unrounded vowel or . In the system of Greek numerals it also has the value five. It was derived from the Phoenic ...
,
Zeta Zeta (, ; uppercase Ζ, lowercase ζ; , , classical or ''zē̂ta''; ''zíta'') is the sixth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 7. It was derived from the Phoenician alphabet, Phoenician letter zay ...
, and
Theta Sagittae Theta Sagittae (θ Sagittae) is a double star in the northern constellation of Sagitta. With a combined apparent visual magnitude of +6, it is near the limit of stars that can be seen with the naked eye. According to the Bortle scal ...
are each multiple stars whose components can be seen in small telescopes.
V Sagittae V Sagittae or V Sge is a cataclysmic variable in the constellation Sagitta. The system is composed of a main sequence star of about 3.3 solar masses and a white dwarf of about 0.9 solar masses; the fact that the white dwarf is less mass ...
is a
cataclysmic variable In astronomy, cataclysmic variable stars (CVs) are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state. They were initially called novae (), since those with an outburst brightness visible to ...
—a
binary star system 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 ...
composed of a
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 ...
accreting mass of a donor star that is expected to go
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 ...
and briefly become the most luminous star in 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 ...
and one of the brightest stars in our sky around the year 2083. Two star systems in Sagitta are known to have Jupiter-like planets, while a third—
15 Sagittae 15 Sagittae (15 Sge) is a star in the northern constellation Sagitta, located around 58 light years away from the Sun. It is visible to the naked eye as a faint, yellow-hued star with an apparent visual magnitude of 5.80. Considered ...
—has a
brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...
companion.


History

The
ancient Greeks Ancient Greece () was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity (), that comprised a loose collection of culturally and linguistically re ...
called Sagitta 'the arrow', and it was one of the 48 constellations described by
Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...
. It was regarded as the weapon that
Hercules Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures. The Romans adapted the Gr ...
used to kill the eagle () of
Jove Jupiter ( or , from Proto-Italic "day, sky" + "father", thus "sky father" Greek: Δίας or Ζεύς), also known as Jove ( nom. and gen. ), is the god of the sky and thunder, and king of the gods in ancient Roman religion and mytholog ...
that perpetually gnawed
Prometheus In Greek mythology, Prometheus (; , , possibly meaning "forethought")Smith"Prometheus". is a Titans, Titan. He is best known for defying the Olympian gods by taking theft of fire, fire from them and giving it to humanity in the form of technol ...
' liver. Sagitta is located beyond the north border of Aquila, the Eagle. An amateur naturalist, polymath Richard Hinckley Allen proposed that the constellation could represent the arrow shot by Hercules towards the adjacent
Stymphalian birds The Stymphalian birds ( ; ) are a group of voracious birds in Greek mythology. The birds' appellation is derived from their dwelling in a swamp in Stymphalia. Characteristics The Stymphalian birds are man-eating birds with beaks of bronze, sh ...
(which feature in Hercules' sixth labour) who had claws, beaks, and wings of iron, and who lived on human flesh in the marshes of Arcadia—denoted in the sky by the constellations Aquila the Eagle, Cygnus 'the Swan', and Lyra 'the Vulture'—and still lying between them, whence the title
Herculea Herculea was a southern Italian colony of the classical Greek city Megara (or The Megarid) which was located in Magna Graecia on the isthmus across to the Peloponnese, adjacent to Corinth and Attica. Herculea, though not referred to often in the ...
. Greek scholar
Eratosthenes Eratosthenes of Cyrene (; ;  – ) was an Ancient Greek polymath: a Greek mathematics, mathematician, geographer, poet, astronomer, and music theory, music theorist. He was a man of learning, becoming the chief librarian at the Library of A ...
claimed it as the arrow with which
Apollo Apollo is one of the Twelve Olympians, Olympian deities in Ancient Greek religion, ancient Greek and Ancient Roman religion, Roman religion and Greek mythology, Greek and Roman mythology. Apollo has been recognized as a god of archery, mu ...
exterminated the
Cyclopes In Greek mythology and later Roman mythology, the Cyclopes ( ; , ''Kýklōpes'', "Circle-eyes" or "Round-eyes"; singular Cyclops ; , ''Kýklōps'') are giant one-eyed creatures. Three groups of Cyclopes can be distinguished. In Hesiod's ''The ...
. The Romans named it Sagitta. In Arabic, it became ''al-sahm'' 'arrow', though this name became ''Sham'' and was transferred to Alpha Sagittae only. The Greek name has also been mistranslated as 'the loom' and thus in Arabic ''al-nawl''. It was also called ''al-'anaza'' 'pike/javelin'.


Characteristics

The four brightest stars make up an arrow-shaped asterism located due north of the bright star
Altair Altair is the brightest star in the constellation of Aquila (constellation), Aquila and the list of brightest stars, twelfth-brightest star in the night sky. It has the Bayer designation Alpha Aquilae, which is Latinisation of name ...
. Covering 79.9 square degrees and hence 0.194% of the sky, Sagitta ranks 86th of the
88 modern constellations In contemporary astronomy, 88 constellations are recognized by the International Astronomical Union (IAU). Each constellation is a region of the sky bordered by arcs of right ascension and declination, together covering the entire celestial sph ...
by area. Only
Equuleus Equuleus is a faint constellation located just north of the celestial equator. Its name is Latin for "little horse", a foal. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern const ...
and
Crux CRUX is a lightweight x86-64 Linux distribution targeted at experienced Linux users and delivered by a tar.gz-based package system with BSD-style initscripts. It is not based on any other Linux distribution. It also utilizes a ports system ...
are smaller. Sagitta is most readily observed from the late spring to early autumn to northern hemisphere observers, with midnight
culmination In observational astronomy, culmination is the passage of a celestial object (such as the Sun, the Moon, a planet, a star, constellation or a deep-sky object) across the observer's local meridian. These events are also known as meridian tran ...
occurring on 17 July. Its position in the
Northern Celestial Hemisphere The northern celestial hemisphere, also called the Northern Sky, is the Northern Hemisphere, northern half of the celestial sphere; that is, it lies north of the celestial equator. This arbitrary sphere diurnal motion, appears to rotate westward ...
means that the whole
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 ...
is visible to observers north of 69°S. Sagitta is bordered by
Vulpecula Vulpecula is a faint constellation in the northern sky. Its name is Latin for "little fox", although it is commonly known simply as the fox. It was identified in the seventeenth century, and is located in the middle of the Summer Triangle (an ...
to the north,
Hercules Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures. The Romans adapted the Gr ...
to the west, Aquila to the south, and
Delphinus Delphinus is a small constellation in the Northern Celestial Hemisphere, close to the celestial equator. Its name is the Latin version for the Greek word for dolphin (). It is one of the 48 constellations listed by the 2nd-century astronomer Pt ...
to the east. The 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 "Sge"; American astronomer
Henry Norris Russell Henry Norris Russell ForMemRS HFRSE FRAS (October 25, 1877 – February 18, 1957) was an American astronomer who, along with Ejnar Hertzsprung, developed the Hertzsprung–Russell diagram (1910). In 1923, working with Frederick Saunders, he ...
, who devised the code, had to resort to using the
genitive In grammar, the genitive case ( abbreviated ) is the grammatical case that marks a word, usually a noun, as modifying another word, also usually a noun—thus indicating an attributive relationship of one noun to the other noun. A genitive can ...
form of the name to come up with a letter to include ('e') that was not in the name of the constellation Sagittarius. 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".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 , while the
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 ...
coordinates are between 16.08° and 21.64°.


Notable features


Stars

Celestial cartographer
Johann Bayer Johann Bayer (; 1572 – 7 March 1625) was a German lawyer and uranographer (celestial cartographer). He was born in Rain in 1572. In 1592, aged 20, he began his study of philosophy and law at the University of Ingolstadt, after which he ...
gave
Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...
s to eight stars, labelling them Alpha to Theta. English astronomer
John Flamsteed John Flamsteed (19 August 1646 – 31 December 1719) was an English astronomer and the first Astronomer Royal. His main achievements were the preparation of a 3,000-star catalogue, ''Catalogus Britannicus'', and a star atlas called '' Atlas ...
added the letters x, mistaken as
Chi __NOTOC__ Chi may refer to: __NOTOC__ Greek *Chi (letter) (Χ or χ), the twenty-second letter of the Greek alphabet Chinese * ''Chi'' (length) (尺), a traditional unit of length, about ⅓ meter *Chi (mythology) (螭), a dragon * Chi (surname) ...
(χ), y and z to 13, 14, and 15 Sagittae in his ''Catalogus Britannicus''. All three were dropped by later astronomers
John Bevis John Bevis (10 November 1695 – 6 November 1771) was an English medical doctor, electrical researcher and astronomer. He is best known for discovering the Crab Nebula in 1731. He was educated at Christ Church, Oxford, being awarded his ...
and
Francis Baily Francis Baily (28 April 177430 August 1844) was an English astronomer. He is most famous for his observations of " Baily's beads" during a total eclipse of the Sun. Baily was also a major figure in the early history of the Royal Astronomical S ...
.


Bright stars

Ptolemy saw the constellation's brightest star
Gamma Sagittae Gamma Sagittae, Latinized from γ Sagittae, is the brightest star in northern constellation of Sagitta. A single star, it is visible to the naked eye with an apparent visual magnitude of +3.47. Based upon an annual parallax sh ...
as marking the arrow's head, while Bayer saw Gamma, Eta, and Theta as depicting the arrow's shaft. Gamma Sagittae is a
red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...
of spectral type M0 III, and magnitude 3.47. It lies at a distance of from Earth. With around 90% of the Sun's mass, it has a radius 54 times that of the Sun and is 575 times as bright. It is most likely on the
red-giant branch The red-giant branch (RGB), sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of stellar evolution. It is a stage that follows the main sequence for low- to intermediate-mass st ...
of its
evolutionary Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certa ...
lifespan, having exhausted its core hydrogen and now burning it in a surrounding shell.
Delta Sagittae Delta Sagittae (Delta Sge, δ Sagittae, δ Sge) is a binary star in the constellation of Sagitta, with an apparent magnitude of +3.68. The primary component is a red M-type bright giant, and the secondary is a B-type main ...
is the second-brightest star in the constellation and is a binary. Delta and Zeta depicted the spike according to Bayer. The Delta Sagittae system is composed of a
red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) and a stellar classification K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelg ...
of spectral type M2 II that has 3.9 times the Sun's mass and 152 times its radius and a blue-white B9.5V
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 that is 2.9 times as massive as the Sun. The two orbit each other every ten years.
Zeta Sagittae Zeta Sagittae (ζ Sagittae) is triple star system in the northern constellation of Sagitta. It is visible to the naked eye, having a combined apparent visual magnitude of +5.00. Based upon an annual parallax shift of , the distance ...
is a triple star system, approximately from Earth. The primary and secondary are A-type stars. In his ''Uranometria'', Bayer depicted Alpha,
Beta Beta (, ; uppercase , lowercase , or cursive ; or ) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Ancient Greek, beta represented the voiced bilabial plosive . In Modern Greek, it represe ...
, and
Epsilon Sagittae Epsilon Sagittae (ε Sagittae) is a solitary, yellow-hued star in the northern constellation of Sagitta. With an apparent visual magnitude of +5.64 to +5.67, it is faintly visible to the naked eye on a dark night. It is a variable sta ...
as the fins of the arrow. Also known as Sham, Alpha is a yellow
bright giant A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzspr ...
star of
spectral class 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 ...
G1 II 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 4.38, which lies at a distance of from Earth. Four times as massive as the Sun, it has swollen and brightened to 21 times the Sun's radius and 340 times its
luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...
. Also of magnitude 4.38, Beta is a G-type
giant In folklore, giants (from Ancient Greek: ''wiktionary:gigas, gigas'', cognate wiktionary:giga-, giga-) are beings of humanoid appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''gia ...
located distant from Earth. Estimated to be around 129 million years old, it is 4.33 times as massive as the Sun, and has expanded to roughly 27 times its radius. Epsilon Sagittae is a
double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a ...
whose component stars can be seen in a small telescope. With an apparent magnitude of 5.77, the main star is a 331-million-year-old yellow giant of spectral type G8 III around 3.09 times as massive as the Sun, that has swollen to its radius. It is distant. The visual companion of magnitude 8.35 is 87.4 
arcseconds 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 ...
distant, but is an unrelated
blue supergiant A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant. They are usually considered to be those with luminosity class I and spectral class B9 or earlier, although sometimes A-class supergiants are also deemed blu ...
around distant from Earth. Eta Sagittae is an orange giant of spectral class K2 III with a magnitude of 5.09. Located from Earth, it has a 61.1% chance of being a member of the
Hyades Hyades may refer to: *Hyades (band) *Hyades (mythology) *Hyades (star cluster), an open star cluster in the constellation Taurus {{Disambiguation it:Iadi ...
Pleiades The Pleiades (), also known as Seven Sisters and Messier 45 (M45), is an Asterism (astronomy), asterism of an open cluster, open star cluster containing young Stellar classification#Class B, B-type stars in the northwest of the constellation Tau ...
stream of stars that share a common motion through space.
Theta Sagittae Theta Sagittae (θ Sagittae) is a double star in the northern constellation of Sagitta. With a combined apparent visual magnitude of +6, it is near the limit of stars that can be seen with the naked eye. According to the Bortle scal ...
is a double star system, with components 12 arcseconds apart visible in a small telescope. At magnitude 6.5, the brighter is a yellow-white main sequence star of spectral type F3 V, located from Earth. The 8.8-magnitude fainter companion is a main sequence star of spectral type G5 V. A 7.4-magnitude orange giant of spectral type K2 III is also visible from the binary pair, located away.


Variable stars

Variable stars are popular targets for amateur astronomers, their observations providing valuable contributions to understanding star behaviour. R Sagittae is a member of the rare RV Tauri variable class of star. It ranges in magnitude from 8.2 to 10.4. It is around distant. It has a radius times that of the Sun, and is as luminous, yet most likely is less massive than the Sun. An aging star, it has moved on from the
asymptotic giant branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...
of stellar evolution and is on its way to becoming a
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 ...
. FG Sagittae is a "born again" star, a highly luminous star around distant from Earth. It reignited fusion of a helium shell shortly before becoming a white dwarf, and has expanded first to a blue supergiant and then to a K-class
supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute visual magnitudes between about −3 and −8. The temperatures of supergiant stars range ...
in less than 100 years. It is surrounded by a faint (visual magnitude 23) planetary nebula, Henize 1–5, that formed when FG Sagittae first left the asymptotic giant branch. S Sagittae is a
classical Cepheid Classical Cepheids are a type of Cepheid variable star. They are young, population I variable stars that exhibit regular radial pulsations with periods of a few days to a few weeks and visual amplitudes ranging from a few tenths of a magnitude u ...
that varies from magnitude 5.24 to 6.04 every 8.38 days. It is a yellow-white supergiant that pulsates between spectral types F6 Ib and G5 Ib. Around 6 or 7 times as massive and 3,500 times as luminous as the Sun, it is located around from Earth. HD 183143 is a remote highly luminous star around away, that has been classified as a blue
hypergiant A hypergiant ( luminosity class 0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds. The term ''hypergiant'' is defined as luminosity class 0 (zero) in the MK ...
.
Infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
bands of ionised
buckminsterfullerene Buckminsterfullerene is a type of fullerene with the formula . It has a cage-like fused-ring structure ( truncated icosahedron) made of twenty hexagons and twelve pentagons, and resembles a football. Each of its 60 carbon atoms is bonded to i ...
molecules have also been found in its spectrum.
WR 124 WR 124 is a Wolf–Rayet star in the constellation of Sagitta surrounded by a ring nebula of expelled material known as M1-67. It is one of the fastest runaway stars in the Milky Way with a radial velocity around . It was discovered by ...
is a
Wolf–Rayet star Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectroscopy, spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very ...
moving at great speed surrounded by a nebula of ejected gas. U Sagittae is an eclipsing binary that varies between magnitudes 6.6 and 9.2 over 3.4 days, making it a suitable target for enthusiasts with small telescopes. There are two component stars—a blue-white star of spectral type B8 V and an ageing star that has cooled and expanded into a yellow subgiant of spectral type G4 III-IV. They orbit each other close enough that the cooler subgiant has filled its
Roche lobe In astronomy, the Roche lobe is the region around a star in a binary system within which orbiting material is gravitationally bound to that star. It is an approximately teardrop-shaped region bounded by a critical gravitational equipotential, ...
and is passing material to the hotter star, and hence it is a semidetached binary system. The system is distant. Near U Sagittae is X Sagittae, a
semiregular variable In astronomy, a semiregular variable star, a type of variable star, is a Red giant, giant or supergiant of intermediate and late (cooler) spectral type. It shows considerable periodicity in its light changes, accompanied or sometimes interrupted b ...
ranging between magnitudes 7.9 and 8.4 over 196 days. A
carbon star A carbon star (C-type star) is typically an asymptotic giant branch star, a luminous red giant, whose Stellar atmosphere, atmosphere contains more carbon than oxygen. The two elements combine in the upper layers of the star, forming carbon monox ...
, X Sagittae has a surface temperature of . Located near 18 Sagittae is
V Sagittae V Sagittae or V Sge is a cataclysmic variable in the constellation Sagitta. The system is composed of a main sequence star of about 3.3 solar masses and a white dwarf of about 0.9 solar masses; the fact that the white dwarf is less mass ...
, the prototype of the V Sagittae variables,
cataclysmic variable In astronomy, cataclysmic variable stars (CVs) are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state. They were initially called novae (), since those with an outburst brightness visible to ...
s that are also super soft X-ray sources. It is expected to become a
luminous red nova A luminous red nova (abbr. ''LRN'', pl. ''luminous red novae'', pl.abbr. ''LRNe'') is a stellar explosion thought to be caused by the merging of two stars. They are characterised by a distinct red colour, and a light curve that fades slowly with ...
when the two stars merge around the year 2083, and briefly become the most luminous star in 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 ...
and one of the brightest stars in Earth's sky.
WZ Sagittae WZ Sagittae (''WZ Sge'') is a dwarf nova cataclysmic star system in the constellation Sagitta. It consists of a white dwarf primary being orbited by a low mass companion. The white dwarf is about 0.85 solar masses while the companion is ...
is another cataclysmic variable, composed of a
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 ...
that has about 85% the mass of the Sun, and low-mass star companion that has been calculated to be a
brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...
of spectral class L2 that is only 8% as massive as the Sun. Normally a faint object dimmer than magnitude 15, it flared up in 1913, 1946 and 1978 to be visible in binoculars. The black widow pulsar (B1957+20) is the second
millisecond pulsar A millisecond pulsar (MSP) is a pulsar with a rotational period less than about 10 milliseconds. Millisecond pulsars have been detected in radio pulsar, radio, X-ray pulsar, X-ray, and gamma ray portions of the electromagnetic spectrum. The leadi ...
ever discovered. It is a massive
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 ...
that is ablating its brown dwarf-sized companion which causes the pulsar's radio signals to
attenuate In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable at ...
as they pass through the outflowing material.


Stars with exoplanets

HD 231701 is a yellow-white main sequence star hotter and larger than the Sun, with 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 A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...
that was discovered in 2007 by the radial velocity technique. The planet orbits at a distance of from the star with a period of 141.6 days. It has a mass of at least 1.13 Jupiter masses. HAT-P-34 is a star times as massive as the Sun with times its radius and times its luminosity. With an apparent magnitude of 10.4, it is distant. A planet times as massive as Jupiter was discovered transiting it in 2012. With a period of 5.45 days and a distance of from its star, it has an estimated surface temperature of .
15 Sagittae 15 Sagittae (15 Sge) is a star in the northern constellation Sagitta, located around 58 light years away from the Sun. It is visible to the naked eye as a faint, yellow-hued star with an apparent visual magnitude of 5.80. Considered ...
is a
solar analog Solar-type stars, solar analogs (also analogues), and solar twins are stars that are particularly similar to the Sun. The stellar classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-type. ...
—a star similar to the Sun, with times its mass, times its radius and times its luminosity. It has an apparent magnitude of 5.80. It has an L4 brown dwarf substellar companion that is around the same size as Jupiter but 69 times as massive with a surface temperature of between 1,510 and , taking around 73.3 years to complete an orbit around the star. The system is estimated to be billion years old.


Deep-sky objects

The band of the Milky Way and the Great Rift within it pass though Sagitta, with Alpha, Beta and Epsilon Sagittae marking the Rift's border. Located between Beta and Gamma Sagittae is
Messier 71 Messier 71 (also known as M71, NGC 6838, or the Angelfish Cluster) is a globular cluster in the small northern constellation Sagitta. It was discovered by Philippe Loys de Chéseaux in 1745 and included by Charles Messier in his catalog of non ...
, a very loose
globular cluster A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...
mistaken for some time for a dense
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 ...
. At a distance of about from Earth, it was first discovered by the French astronomer
Philippe Loys de Chéseaux Jean-Philippe Loys de Cheseaux (; 4 May 1718 – 30 November 1751) was a Swiss astronomer. Biography Loys de Cheseaux was born on 4 May 1718 in Lausanne, Vaud, to Paul-Etienne Loys de Cheseaux, a banneret, and Estienne-Judith de Crousaz. His ...
in the year 1745 or 1746. The loose globular cluster has a mass of around and a
luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...
of approximately 19,000 . There are two notable
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 ...
e in Sagitta: NGC 6886 is composed of a hot central post-AGB star that has 55% of the Sun's mass yet times its luminosity, with a surface temperature of , and surrounding nebula estimated to have been expanding for between 1,280 and 1,600 years, The nebula was discovered by
Ralph Copeland Ralph Copeland FRSE FRAS (3 September 1837 – 27 October 1905) was an English astronomer and the third Astronomer Royal for Scotland. Life Copeland was born at Moorside Farm, near Woodplumpton in Lancashire, England the son of Robert Cope ...
in 1884. The Necklace Nebula—originally a close binary, one component of which swallowed the other as it expanded to become a giant star. The smaller star remained in orbit inside the larger, whose rotation speed increased greatly, resulting in it flinging its outer layers off into space, forming a ring with knots of bright gas formed from clumps of stellar material. It was discovered in 2005 and is around 2 light-years wide.Hubble Offers a Dazzling View of the 'Necklace' Nebula
news release STScI-2011-24 dated August 11, 2011, from
Space Telescope Science Institute The Space Telescope Science Institute (STScI) is the science operations center for the Hubble Space Telescope (HST), science operations and mission operations center for the James Webb Space Telescope (JWST), and science operations center for the ...
It has a size of . Both nebulae are around from Earth.


See also

* Sagitta (Chinese astronomy)


Notes


References


External links


The Deep Photographic Guide to the Constellations: Sagitta

Warburg Institute Iconographic Database (ca 160 medieval and early modern images of Sagitta)
* Bayer's
Uranometria
'', from the
Linda Hall Library The Linda Hall Library is a privately endowed American library of science, engineering and technology located in Kansas City, Missouri, on the grounds of a urban arboretum. It claims to be the "largest independently funded public library of sc ...
digital collection. {{featured article Articles containing video clips Constellations Constellations listed by Ptolemy Mythological weapons Mythology of Heracles Northern constellations Objects in Greek mythology