Delphinus

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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 ({{#invoke:Lang|lang}}). It is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and remains one of the 88 modern constellations recognized by the International Astronomical Union. It is one of the smaller constellations, ranked 69th in size. Delphinus' five brightest stars form a distinctive asterism symbolizing a dolphin with four stars representing the body and one the tail. It is bordered (clockwise from north) by Vulpecula, Sagitta, Aquila, Aquarius, Equuleus and Pegasus.

Delphinus is a faint constellation with only two stars brighter than an apparent magnitude of 4, Beta Delphini (Rotanev) at magnitude 3.6 and Alpha Delphini (Sualocin) at magnitude 3.8.

MythologyEdit

File:Sidney Hall - Urania's Mirror - Delphinus, Sagitta, Aquila, and Antinous.jpg

Delphinus is depicted on the left of this card from Urania's Mirror (1825)

Delphinus is associated with two stories from Greek mythology.

According to myth, the first Greek god Poseidon wanted to marry Amphitrite, a beautiful nereid. However, wanting to protect her virginity, she fled to the Atlas Mountains. Her suitor then sent out several searchers, among them a certain Delphinus. Delphinus accidentally stumbled upon her and persuaded Amphitrite to accept Poseidon's wooing. Out of gratitude, the god placed the image of a dolphin among the stars.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The second story tells of the Greek poet Arion of Lesbos (7th century BC), who a dolphin saved.Template:Sfn He was a court musician at the palace of Periander, ruler of Corinth. Arion had amassed a fortune during his travels to Sicily and Italy. On his way home from Tarentum, his wealth caused the crew of his ship to conspire against him. Threatened with death, Arion asked to be granted a last wish, which the crew granted: he wanted to sing a dirge.<ref>Herodotus, Histories I.23-24;
also Aulus Gellius, Noctes Atticae XVI.19; Plutarch, Conv. sept. sap. 160–62; Shakespeare, Twelfth Night (Act I, Sc 2, line 16)</ref> This he did, and while doing so, flung himself into the sea. There, he was rescued by a dolphin which had been charmed by Arion's music. The dolphin carried Arion to the coast of Greece and left.<ref name="S&T">Template:Cite journal</ref>

In non-Western astronomyEdit

In Chinese astronomy, the stars of Delphinus are located within the Black Tortoise of the North (北方玄武, Běi Fāng Xuán Wǔ).<ref>Template:In lang AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 4 日</ref>

In Polynesia, two cultures recognized Delphinus as a constellation. In Pukapuka, it was called Te Toloa and in the Tuamotus, it was called Te Uru-o-tiki.Template:Sfn

In Hindu astrology, the Delphinus corresponds to the Nakshatra, or lunar mansion, of Dhanishta.

CharacteristicsEdit

Delphinus is bordered by Vulpecula to the north, Sagitta to the northwest, Aquila to the west and southwest, Aquarius to the southeast, Equuleus to the east and Pegasus to the east.<ref name="boundary" /> Covering 188.5 square degrees, corresponding to 0.457% of the sky, it ranks 69th of the 88 constellations in size.<ref name=tirionconst>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The three-letter abbreviation for the constellation, as adopted by the IAU in 1922, is "Del".<ref name="pa30_469">Template:Cite journal</ref> The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of 14 segments. 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 Template:DEC and Template:DEC.<ref name="boundary" /> The whole constellation is visible to observers north of latitude 69°S.<ref name=tirionconst/>Template:Efn

FeaturesEdit

File:DelphinusCC.jpg

The constellation Delphinus as it can be seen by the naked eye

File:Del 20191202.jpg

Contrast and color enhanced photograph of Delphinus

StarsEdit

Template:See also Delphinus has two stars above fourth (apparent) magnitude; its brightest star is of magnitude 3.6. The main asterism in Delphinus is Job's Coffin, nearly a 45°-apex lozenge or diamond of the four brightest stars: Alpha, Beta, Gamma, and Delta Delphini. Delphinus is in a rich Milky Way star field. Alpha and Beta Delphini have 19th-century names Sualocin and Rotanev, read backwards: Nicolaus Venator, the Latinized name of a Palermo Observatory director, Niccolò Cacciatore (d. 1841).Template:Sfn

Alpha Delphini is a blue-white hued main sequence star of magnitude 3.8,<ref name=oja>Template:Cite journal</ref> 241 light-years from Earth. It is a spectroscopic binary.<ref name=malkov>Template:Cite journal</ref> It is officially named Sualocin.<ref name=Kunitzsch>Template:Cite book</ref><ref name=Sualocin>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The star has an absolute magnitude of -0.4.<ref name=mv>Template:Cite journal</ref>

Beta Delphini is officially called Rotanev.<ref name=Kunitzsch/> It was found to be a binary star in 1873.<ref name=burnham1978>Template:Citation</ref> The gap between its close binary stars is visible from large amateur telescopes. To the unaided eye, it appears to be a white star of magnitude 3.6.<ref name=aj138_5_1354>Template:Citation</ref><ref name=burnham1978 /> It has a period of 27 years and is 97 light-years from Earth.

Gamma Delphini is a celebrated binary star among amateur astronomers. The primary is orange-gold of magnitude 4.3; the secondary is a light yellow star of magnitude 5.1. The pair forms a true binary with an estimated orbital period of over 3,000 years. 125 light-years away, the two components are visible in a small amateur telescope.Template:Sfn The secondary, also described as green, is 10 arcseconds from the primary. Struve 2725, called the "Ghost Double", is a pair that appears similar but dimmer. Its components of magnitudes 7.6 and 8.4 are separated by 6 arcseconds and are 15 arcminutes from Gamma Delphini itself.<ref name="S&T"/> An unconfirmed exoplanet with a minimum mass of 0.7 Jupiter masses may orbit one of the stars.<ref name=Irwin_et_al_1999>Template:Citation</ref><ref name="Wittemeyer et al.">Template:Cite journal</ref>

Delta Delphini is a type A-type star<ref name=gray2001>Template:Citation</ref> of magnitude 4.43.<ref name=Chang2013>Template:Citation</ref> It is a spectroscopic binary, and both stars are Delta Scuti variables.<ref name=Liakos2017>Template:Citation</ref>

Epsilon Delphini, Deneb Dulfim (lit. "tail [of the] Dolphin"), or Aldulfin, is a star of stellar class B6 III.<ref name=Lesh1968>Template:Citation</ref> Its magnitude is variable at around 4.03.<ref>Template:Citation</ref><ref name=Crawford1971>Template:Citation</ref>

Zeta Delphini, an A3Va<ref name=Zeta /> main-sequence star of magnitude 4.6, was in 2014 discovered to have a brown dwarf orbiting around it. Zeta Delphini B has a mass of 50±15 Template:Jupiter mass.<ref name=Zeta>Template:Cite journal</ref>

File:Aquila.fade-in.animation.webm

Animation fading-in of Aquila, Delphinus, Sagitta, and the summer Milky Way as seen in Dark-sky preserve Westhavelland

Rho Aquilae at magnitude 4.94<ref name=scfs /> is at about 150 light-years away.<ref name=scfs>Template:Citation</ref> Due to its proper motion, it has been in the (round-figure parameter) bounds of the constellation since 1992.<ref>Template:Cite book</ref> It is an A-type main sequence star with a lower metallicity than the Sun.<ref name=starhorse>Template:Citation</ref>

HR Delphini was a nova that brightened to magnitude 3.5 in December 1967.<ref name=isles67>Template:Cite journal</ref> It took an unusually long time for the nova to reach peak brightness which indicate that it barely satisfied the conditions for a thermonuclear runaway.<ref>Template:Cite journal</ref> Another nova by the name V339 Delphini was detected in 2013; it peaked at magnitude 4.3 and was the first nova observed to produce lithium.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Musica, also known by its Flamsteed designation 18 Delphini, is one of the five stars with known planets located in Delphinus. It has a spectral type of G6 III.<ref>Template:Cite journal</ref> Arion, the planet, is a very dense and massive planet with a mass at least 10.3 times greater than Jupiter.<ref>Template:Cite journal</ref> Arion was part of the first NameExoWorlds contest where the public got the opportunity to suggest names for exoplanets and their host stars.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

ExoplanetsEdit

In 2024 the planet TOI-6883 b was discovered in the constellation Delphinus.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It has a 16.249 day orbital period around its host star,<ref name=":0">Template:Cite journal</ref> a radius 1.08 times Jupiter's,<ref name=":1">Template:Cite journal</ref> and a mass 4.34 times Jupiter's.<ref name=":0" /> It was discovered from a single transit<ref name=":1" /> in TESS data and it was confirmed by a network of citizen scientists.<ref name=":0" />

In 2024, the planet TOI-6883 c was discovered in the constellation Delphinus.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It has an orbital period of 7.8458 days, a radius of 0.7 times Jupiter's, and a third of Jupiter's mass. The Neptunian-size planet was discovered from an abnormality in data retrieved from TOI-6883 c.<ref>Template:Cite arXiv</ref>

Deep-sky objectsEdit

Its rich Milky Way star field means many modestly deep-sky objects. NGC 6891 is a planetary nebula of magnitude 10.5; another is NGC 6905 or the Blue Flash Nebula. The Blue Flash Nebula shows broad emission lines. The central star in NGC 6905 has a spectral type of WO2, meaning it is rich in oxygen.<ref name=GomezGonzalez>Template:Cite journal</ref>

NGC 6934 is a globular cluster of magnitude 9.75. It is about 52,000 light-years away from the Solar System.<ref>Template:Cite journal</ref> It is in the Shapley-Sawyer Concentration Class VIII<ref name=ShapleySawyer>Template:Citation</ref> and is thought to share a common origin with another globular cluster in Boötes.<ref name=apj670_1_363>Template:Citation</ref> It has an intermediate metallicity for a globular cluster,<ref name=Kaluzny2001>Template:Cite journal</ref> but as of 2018 it has been poorly studied.<ref>Template:Cite journal</ref> At a distance of about 137,000 light-years,<ref name=apj670_1_363 /> the globular cluster NGC 7006 is at the outer reaches of the galaxy. It is also fairly dim at magnitude 11.5 and is in Class I.<ref name=ShapleySawyer />