Delphinus (Eng. U.S. /dɛlˈfnəs/) Eng. oth: /ˈdɛlfɪnəs/) is a constellation in the northern sky, close to the celestial equator. Its name is Latin for dolphin. Delphinus was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains among the 88 modern constellations recognized by the International Astronomical Union. It is one of the smaller constellations, ranked 69th in size.

Pronunciation/dɛlˈfnəs/ Delfínus, genitive /dɛlˈfn/
Right ascension 21h
Area189 sq. deg. (69th)
Main stars5
Stars with planets5
Stars brighter than 3.00m0
Stars within 10.00 pc (32.62 ly)2
Brightest starRotanev (β Del) (3.63m)
Messier objects0
Meteor showersNone
Visible at latitudes between +90° and −70°.
Best visible at 21:00 (9 p.m.) during the month of September.

Delphinus' brightest stars form a distinctive asterism that can easily be recognized. It is bordered (clockwise from north) by Vulpecula the fox, Sagitta the arrow, Aquila the eagle, Aquarius the water-carrier, Equuleus the foal and Pegasus the flying horse.


Notable featuresEdit

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


Delphinus lacks stars above fourth (apparent) magnitude; its brightest star is of magnitude 3.8. The main asterism in Delphinus is Job's Coffin, nearly a 45°-apex lozenge 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).[1]

Alpha Delphini is a blue-white hued main sequence star of magnitude 3.8, 241 light-years from Earth.

Beta Delphini, called Rotanev. 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. 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 form 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.[1] 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.[2]

Delta Delphini is a type A7 IIIp star of magnitude 4.43.

Epsilon Delphini, Deneb Dulfim (lit. "tail [of the] Dolphin"), or Aldulfin, is a star of stellar class B6 III and magnitude 4, at 330 ly.[3]

In Delphinus, in extremes of distance, Gliese 795 is the closest known star at 54.95 ly and rapidly moves east over a period of centuries (863±3 arcseconds per year); whereas the giant of blue colour, W Delphini is at 2203.81 ly at 9.76 magnitude.[3] Its brightness ranges from a magnitude of 12.3 to a magnitude of 9.7 over its variable period as it is a Beta Persei star-type semi-detached system. Other variable stars of large amateur telescopic visibility include R Delphini, a Mira-type variable star with a period of 285.5 days. Its magnitude ranges between a maximum 7.6 and a minimum 13.8.

Rho Aquilae at magnitude 4.94 is at about 150 light years.[4] Due to its proper motion it has been in the (round-figure parameter) bounds of the constellation since 1992.

HR Delphini was a nova that brightened to magnitude 3.5 in December 1967.[5] A nova was discovered by amateur astronomer Koichi Itagaki, Nova Delphini 2013.[6][7][8]


Giants within our galaxy in Delphinus aside from Delta, Gamma and Epsilon include:[3]

Name Colour Type Distance (in ly)
Eta Delphini White subgiant 236.18
Kappa Delphini Yellow subgiant 98.24
10 Delphini Orange giant 507.25
17 Delphini Orange giant 479.65
Musica or 18 Delphini Yellow giant 245.60
EU Delphini Red giant 381.03
LU Delphini Yellow giant 485.36
U Delphini Red giant 1568.09
Theta Delphini Orange supergiant 2013.35

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. NGC 6934 is a globular cluster of magnitude 9.75. At a distance of about 185,000 light-years, the globular cluster NGC 7006 is at the outer reaches of the galaxy. It is also fairly dim at magnitude 11.5.


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 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 was able to persuade Amphitrite to accept Poseidon's wooing. Out of gratitude the god placed the image of a dolphin among the stars.[9][10]

The second story tells of the Greek poet Arion of Lesbos (7th century BC), who was saved by a dolphin.[1] 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.[11] 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.[2]


In Chinese astronomy, the stars of Delphinus are located within the Black Tortoise of the North (北方玄武, Běi Fāng Xuán Wǔ).[12]

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.[13]


USS Delphinus (AF-24) and USS Delphinus (PHM-1), two United States Navy ships, are named after the constellation.

A house at Sutton Girls is named Delphinus

See alsoEdit


  1. ^ a b c Ridpath & Tirion 2017, pp. 140-141.
  2. ^ a b Schaaf, Fred (September 2012). "The Celestial Dolphin". Sky and Telescope: 47.
  3. ^ a b c
  4. ^ Wielen, R.; et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions (35), Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W.
  5. ^ Isles, J. E. (1974). "HR Delphini (Nova 1967) in 1967 - 71". Journal of the British Astronomical Association. 85: 54–58. Bibcode:1974JBAA...85...54I.
  6. ^ King, Bob (August 14, 2013). "Bright New Nova In Delphinus — You can See it Tonight With Binoculars". Universe Today (initial designation PNV J20233073+2046041). Retrieved August 15, 2013.
  7. ^ Guido, Ernesto; Ruocco, Nello; Howes, Nick (August 15, 2013). "Possible Bright Nova in Delphinus". Associazione Friulana di Astronomia e Meteorologia. Retrieved August 15, 2013.
  8. ^ Masi, Gianluca (August 15, 2013). "Nova Delphini 2013 (formerly PNV J20233073+2046041): images, spectra and maps". Gianluca Masi - Virtual Telescope Project. Retrieved August 15, 2013.
  9. ^ Pseudo-Hyginus. "HYGINUS, ASTRONOMICA 2.1-17". Theoi Classical Texts Library. Retrieved June 26, 2017.
  10. ^ Ravensdale, Kaede. "Never Cry Werewolf".
  11. ^ 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)
  12. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 4 日
  13. ^ Makemson 1941, p. 283.


External linksEdit