Delphinus 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.
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.
[http://www.peoplesguidetothecosmos.com/constellations/delphinus.htm]
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. She, however, wanting to protect her virginity, 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.
The second story tells of the Greek poet Arion of Lesbos (7th century BCE), who was saved by a dolphin. 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. 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.
In Chinese astronomy, the stars of Delphinus are located within the Black Tortoise of the North (Běi Fāng Xuán Wǔ).
In Polynesia, two cultures recognized Delphinus as a constellation. On Pukapuka, it was called Te Toloa and in the Tuamotus, it was called Te Uru-o-tiki.
[http://www.space.com/22389-nova-star-explosion-delphinus-discovery.html]
Delphinus does not have any bright stars; its brightest star is of magnitude 3.8. However, Delphinus is in a rich Milky Way star field. The main asterism in Delphinus forms a diamond, or ‘Job’s Coffin,’ from the four brightest stars: Alpha, Beta, Gamma, and Delta Delphini. Alpha and Beta Delphini are named Sualocin and Rotanev, respectively. When read backwards, they read as Nicolaus Venator, the Latinized name of Palermo Observatory’s former director, Niccolò Cacciatore.
Alpha Delphini (Sualocin) is a blue-white hued main sequence star of magnitude 3.8, 241 light-years from Earth.
Beta Delphini (Rotanev) is a close binary star and the brightest in Delphinus, divisible in only 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 a gold-colored star of magnitude 4.3 and the secondary is a yellow-tinged star of magnitude 5.1. 102 light-years away, the components of Gamma Delphini are divisible in a small amateur telescope. The secondary, also described as green, is 10 arcseconds from the primary.
Delta Delphini is a giant star of magnitude 4.43.
Epsilon Delphini, called also Deneb Dulfim, ‘tail of the Dolphin,’ is a blue-white giant star of magnitude 4.
Delphinus is also home to several variable stars. R Delphini is a Mira-type variable star with a period of 285.5 days. Its magnitude ranges between a maximum of 7.6 and a minimum of 13.8.
HR Delphini was a nova that brightened to magnitude 3.5 in December 1967. On 14 August 2013, a possible nova was discovered by amateur astronomer Koichi Itagaki, initially labelled PNV J20233073+2046041, now labelled Nova Delphini 2013.
Because it is in a rich Milky Way star field, Delphinus has several deep-sky objects.
NGC 6934 by Hubble Space Telescope
NGC 6934 (also known as Caldwell 47) is a globular cluster in the constellation Delphinus, about 50,000 light years distant. It was discovered by William Herschel on 24 September 1785.
[https://en.wikipedia.org/wiki/NGC_6934]
NGC 7006
NGC 7006 (also known as Caldwell 42) is a globular cluster in the constellation Delphinus. NGC 7006 resides in the outskirts of the Milky Way. It is about 135,000 light-years away, five times the distance between the Sun and the center of the galaxy, and it is part of the galactic halo. This roughly spherical region of the Milky Way is made up of dark matter, gas and sparsely distributed stellar clusters.
NGC 7006 appears in the science fiction novel Beyond the Farthest Star by Edgar Rice Burroughs, where it is used as a point of reference by the inhabitants of the planet Poloda to determine the approximate location of Earth.
[https://en.wikipedia.org/wiki/NGC_7006]
NGC 6905 in Delphinus
[http://www.capella-observatory.com/ImageHTMLs/PNs/NGC6905.htm]
One notable planetary nebula is NGC 6905 or the Blue Flash nebula. It was discovered by William Herschel in 1784. The shape of the nebula is characterized by an internal shell with roughly conical extensions, with ansae-type formations along the major axis. The central star, a white dwarf is of 14.0 magnitude, and it is estimated to have surface temperature 150.000 K. The distance of NGC 6905, as with most planetary nebulae, is not well determined and estimates range between 1.7 and 2.6 kpc. NGC 6905 can be detected under dark skies with a 4-inch telescope, but it better observed with larger instruments.
[https://en.wikipedia.org/wiki/NGC_6905]
[https://en.wikipedia.org/wiki/Delphinus]
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