Delphinus is a faint constellation with only two stars brighter than anapparent magnitude of 4,Beta Delphini (Rotanev) at magnitude 3.6 andAlpha Delphini (Sualocin) at magnitude 3.8.
Delphinus is depicted on the left of this card fromUrania's Mirror (1825)
Delphinus is associated with two stories fromGreek mythology.
According to myth, the first Greek godPoseidon wanted to marryAmphitrite, a beautifulnereid. 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.[3]
The second story tells of the Greek poetArion ofLesbos (7th century BC), who a dolphin saved.[4] 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 fromTarentum, 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.[5] 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.[6]
InPolynesia, two cultures recognized Delphinus as a constellation. InPukapuka, it was calledTe Toloa and in theTuamotus, it was calledTe Uru-o-tiki.[8]
Delphinus is bordered byVulpecula to the north,Sagitta to the northwest,Aquila to the west and southwest,Aquarius to the southeast,Equuleus to the east andPegasus to the east.[1] Covering 188.5 square degrees, corresponding to 0.457% of the sky, it ranks 69th of the 88 constellations in size.[9] The three-letter abbreviation for the constellation, as adopted by the IAU in 1922, is "Del".[10] The official constellation boundaries, as set byEugène Delporte in 1930, are defined by a polygon of 14 segments. In theequatorial coordinate system, theright ascension coordinates of these borders lie between20h 14m 14.1594s and21h 08m 59.6073s, while thedeclination coordinates are between +2.4021468° and +20.9399471°.[1] The whole constellation is visible to observers north of latitude69°S.[9][a]
Delphinus has two stars above fourth(apparent) magnitude; its brightest star is of magnitude 3.6. The mainasterism in Delphinus is Job's Coffin,[11] nearly a 45°-apexlozenge 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 aPalermo Observatory director,Niccolò Cacciatore (d. 1841).[4]
Alpha Delphini is a blue-white huedmain sequence star of magnitude 3.8,[12] 241 light-years from Earth. It is a spectroscopic binary.[13] It is officially named Sualocin.[14][15] The star has an absolute magnitude of -0.4.[16]
Beta Delphini is officially called Rotanev.[14] It was found to be a binary star in 1873.[17] The gap between its closebinary stars is visible from large amateur telescopes. To the unaided eye, it appears to be a white star of magnitude 3.6.[18][17] 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.[4] 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.[6] An unconfirmed exoplanet with a minimum mass of 0.7 Jupiter masses may orbit one of the stars.[19][20]
Zeta Delphini, an A3Va[27] main-sequence star of magnitude 4.6, was in 2014 discovered to have abrown dwarf orbiting around it. Zeta Delphini B has a mass of 50±15MJ.[27]
Rho Aquilae at magnitude 4.94[28] is at about 150 light-years away.[28] Due to itsproper motion, it has been in the (round-figure parameter) bounds of the constellation since 1992.[29] It is anA-type main sequence star with a lower metallicity than the Sun.[30]
HR Delphini was anova that brightened to magnitude 3.5 in December 1967.[31] 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.[32] Another nova by the nameV339 Delphini was detected in 2013; it peaked at magnitude 4.3 and was the first nova observed to produce lithium.[33][34][35][36]
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.[37]Arion, the planet, is a very dense and massive planet with a mass at least 10.3 times greater than Jupiter.[38] Arion was part of the firstNameExoWorlds contest where the public got the opportunity to suggest names for exoplanets and their host stars.[39]
In 2024 the planetTOI-6883 b was discovered in the constellation Delphinus.[40] It has a 16.249 day orbital period around its host star,[41] a radius 1.08 times Jupiter's,[42] and a mass 4.34 times Jupiter's.[41] It was discovered from a single transit[42] in TESS data and it was confirmed by a network of citizen scientists.[41]
In 2024, the planet TOI-6883 c was discovered in the constellation Delphinus.[43] 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.[44]
Its richMilky Way star field means many modestly deep-sky objects.NGC 6891 is aplanetary nebula of magnitude 10.5; another isNGC 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.[45]
NGC 6934 is aglobular cluster of magnitude 9.75. It is about 52,000 light-years away from the Solar System.[46] It is in theShapley-Sawyer Concentration Class VIII[47] and is thought to share a common origin with another globular cluster inBoötes.[48] It has an intermediate metallicity for a globular cluster,[49] but as of 2018 it has been poorly studied.[50] At a distance of about 137,000 light-years,[48] the globular clusterNGC 7006 is at the outer reaches of the galaxy. It is also fairly dim at magnitude 11.5 and is in Class I.[47]
^While parts of the constellation rise above the horizon to observers between 69°S and87°S, stars within a few degrees of the horizon are practically unobservable.[9]
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^Lesh, Janet Rountree (December 1968), "The Kinematics of the Gould Belt: an Expanding Group?",Astrophysical Journal Supplement,17: 371,Bibcode:1968ApJS...17..371L,doi:10.1086/190179.
^Crawford, D. L.; et al. (1971), "Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere",The Astronomical Journal,76: 1058,Bibcode:1971AJ.....76.1058C,doi:10.1086/111220.
^abWielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions",Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg,35 (35), Astronomisches Rechen-Institut Heidelberg: 1,Bibcode:1999VeARI..35....1W.
^Anders, F.; Khalatyan, A.; Chiappini, C.; Queiroz, A. B.; Santiago, B. X.; Jordi, C.; Girardi, L.; Brown, A. G. A.; Matijevic, G.; Monari, G.; Cantat-Gaudin, T.; Weiler, M.; Khan, S.; Miglio, A.; Carrillo, I.; Romero-Gómez, M.; Minchev, I.; de Jong, R. S.; Antoja, T.; Ramos, P.; Steinmetz, M.; Enke, H. (1 August 2019), "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18",Astronomy and Astrophysics,628: A94,arXiv:1904.11302,Bibcode:2019A&A...628A..94A,doi:10.1051/0004-6361/201935765,ISSN0004-6361,S2CID131780028.
^Isles, J. E. (1974). "HR Delphini (Nova 1967) in 1967 - 71".Journal of the British Astronomical Association.85:54–58.Bibcode:1974JBAA...85...54I.
^Guido, Ernesto; Ruocco, Nello; Howes, Nick (August 15, 2013)."Possible Bright Nova in Delphinus". Associazione Friulana di Astronomia e Meteorologia. RetrievedAugust 15, 2013.
^Conzo, G.; Leiner, N.; Lynch, K.; Moriconi, M.; Ruocco, N.; Scarmato, T. (2024-10-09). "TIC 393818343 c: Discovery and characterization of a Neptune-like planet in the Delphinus constellation".arXiv:2410.07425 [astro-ph.EP].
^abShapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters",Harvard College Observatory Bulletin,849 (849):11–14,Bibcode:1927BHarO.849...11S.
