Delphinus

To the ancient Greeks and Romans and even today, the dolphin is portrayed as the most philanthropic of creatures, playful, benevolent, tireless, harmonious and intelligent. Many stories have been played out in books and upon the stage of the dolphin's contribution to humanity and the constellation Delphinus has been so placed in the sky to honour this wonderful marine mammal.

There are three main Greek legends surrounding Delphinus. The first concerns Poseidon (equivalent to the Roman Neptune) who rather fancied the beautiful nymph Amphitrite. Upon hearing of Poseidon's wish to marry her, she fled to Mt Atlas. Not a great start to a relationship in anyone's book but in true Greek Gods tradition, Poseidon sent out searchers including a dolphin to find his prospective bride. It was the dolphin who eventually found her, convinced her that Poseidon wasn't such a bad chap as far as Gods go and brought her back. Once married, Poseidon declared the dolphin sacred and placed its image among the stars.

The second legend appears in Aglaosthene's 'Naxica'. It appears that Tyrrhenian shipmasters were employed to take the child Liber (Dionysos) and his companions to Naxos. On the voyage, the sailors, in reality pirates, decided to kidnap the children and hold them for ransom. Liber, endowed with maturity beyond his years, discovered the plot and ordered his companions to sing. The melodious sound that came forth bewitched the sailors and they excitedly began to dance. In fact, they were so carried away that they accidentally hurled themselves overboard and upon hitting the ocean, changed into dolphins. Liber placed a dolphin image into the sky to celebrate his escape. There are many versions of this tale.

The third legend concerns the poet and musician Arion. Out sailing and no doubt enjoying the salt laden sea air and perhaps a spot of fishing, Arion's slaves decided to mutiny. Preparing to throw Arion overboard into the watery depths, Arion requested that he be allowed to put on his robe that he had often worn in victory. He then began to sing a lament to his coming death. Dolphins from near and far were drawn to his singing and Arion, invoking the power of the Gods, threw himself among the dolphins who whisked him away to the shores of Taenarum. Later, the slaves were caught in a ferocious storm and were beached upon the sands of Taenarum where they were arrested and executed. A statue honouring Arion and the dolphins was placed upon this ground. Asttronomers, to honour the heroic dolphin, placed the constellation of Delphinus into the heavens.

There are nine classical stars that make up Delphinus, each named for the Greek Muses who presided over art and science. These nine Muses were the daughters of all powerful Zeus and Mnemosyne. Their nurse Eupheme and her son Cronus, later to gain fame as the constellation figure Sagittarius, raised them. Their names were Calliope 'Fair Voiced', Clio 'Proclaimer', Erato 'Lovely', Euterpe 'Giver of Pleasure', Melpomene "Songstress', Polyhymnia 'She of Many Hymns', Terpsichore 'Whirler', Thalia 'Flourishing' and Urania 'Heavenly'. This last named Muse was the overseer of astronomy. Tycho Brahe, gifted the island of Ven by King Frederick II,

and built a new observatory there, calling it Uraniborg in honour of Urania.

"Urania, o'er her star-bespangled lyre,

With touch of majesty diffused her soul;

A thousand tones, that in the breast inspire,

Exalted feelings, o er the wires 'gan roll—

She sang of night that clothed the infant world,

In strains as solemn as its dark profound—

How at the call of Jove the mist unfurled,

And o'er the swelling vault—the glowing sky,

The new-born stars hung out their lamps on high,

And rolled their mighty orbs to music's sweetest sound."

~ James G. Percival; An Ode To Music

There is a delightful story regarding the Muses in Plato's 'Phaedrus':

"Socrates: It is quite improper for a lover of the Muses never to have heard of such things. The story goes that these locusts were once men, before the birth of the Muses, and when the Muses were born and song appeared, some of the men were so overcome with delight that they sang and sang, forgetting food and drink, until at last unconsciously they died. From them the locust tribe afterwards arose, and they have this gift from the Muses, that from the time of their birth they need no sustenance, but sing continually, without food or drink, until they die, when they go to the Muses and report who honors each of them on earth. They tell Terpsichore of those who have honored her in dances, and make them dearer to her; they gain the favor of Erato for the poets of love, and that of the other Muses for their votaries, according to their various ways of honoring them; and to Calliope, the eldest of the Muses, and to Urania who is next to her, they make report of those who pass their lives in philosophy and who worship these Muses who are most concerned with heaven and with thought divine and human and whose music is the sweetest. So for many reasons we ought to talk and not sleep in the noontime."

Delphinus is a small constellation of 189 sq.°, about the size of Corvus, lying between Aquila and Pegasus. Look for the kite or diamond shaped figure 14° below and east of the bright star Altair in Aquila, obvious to the naked eye and forming the upper part of our dolphin's body. This grouping, for some obscure reason, is also known as 'Job's Coffin'. Delphinus has 4 stars of 4th magnitude or brighter and another 2 brighter than 5th.

Gamma Delphini represents the nose of the celestial dolphin. Here we have a superb double star of magnitudes 4.3 and 5.1, discovered by F. Struve. They are separated by an easy 9".6, this system lying just over 100 light years distant. Their respective spectral types ore K1 and F7, golden and pale yellow to telescopic observers. The brighter star has a luminosity (brightness) around 16 times that of our Sun whilst the fainter member a luminosity around 7 times.

Around 15' to the south and slightly west lies the fainter pairing of Ʃ2725 (Struve 2725). This pair of magnitudes 7.6 and 8.4 are separated by 6".1 (year 2000) and lie a little further away at around 125 light years. A wide field eyepiece will include this pair and gamma Delphini, making a beautiful double double.

Alpha Delphini lies west of gamma, shining at an apparent magnitude of 3.8, it's real luminosity 141 ±16 Suns. This B-type star lies 241 ±13 light years distant. Alpha is also a spectroscopic binary resolved by speckle interferometry in 1986. There are 5 faint optical companions scattered around alpha's glow, ranging from 10.6 to 13.3 magnitude.

Delta lies southeast of alpha, an A-type giant or possibly F-type subgiant of magnitude 4.4. The distance is 203.5 ±9.0 light years and the luminosity 54.7 ±4.8 Suns.

Completing the diamond shape is beta Delphini, a magnitude 3.6 F-type star lying 97.4 ±3.9 light years away. The luminosity is 26.0 ±2.1 Suns. S.W. Burnham discovered a very close companion in August 1873, the system having a rapid orbital period of 26.65 years.

Beta is known as Rotanev and alpha as Sualocin and for many years the origin of these obscure and unfamiliar names remained uncertain. They first appeared in the Palermo Catalogue of 1814 and in later years, it was discovered by T.W. Webb (Celestial Objects For Common Telescopes) that if written backwards, these names spelt out Nicolaus Venator. He related that his is a Latinised version for Niccolo Cacciatore, an assistant of Piazzi at the Palermo Observatory.

Though Admiral Smythe could make no sense of these names even though he knew Piazzi and Cacciotore:

"α Delphini appears under the cacophonous and barbaric epithet Svalocin, on the Palermo Catalogue. But no poring into the black-letter versions of the Almagest, El Battani, Ibn Yunis, and other authorities, enables one to form any rational conjecture as to the mis-reading, mis-writing, or mis-application, in which so strange a meta-morphosis could have originated."

There are a further 5 classical stars making up the 'dolphin'. They are zeta, eta, epsilon, iota and kappa. Epsilon has the dubious honour of being named Pae Chaou, the 'Rotten Melon' by the Chinese.

There are few deep sky objects of any note in Delphinus. However, two planetary nebulae and two globular clusters are worth a look. Lying on the northwestern border with Sagitta is NGC 6905, a planetary nebula discovered by William Herschel in 1784. Medium mirrors will show a faint glow, slightly elliptical in shape within a small triangle of stars. Larger mirrors are needed to show it at its best, bringing forth a delicate ring with a faint 14th magnitude star and perhaps a hint of the nebula's blue/green colour under good seeing conditions. To northern hemisphere observers, it is known as the 'Blue Flash', possibly first coined by John Mallas in the 1960s. An OIII (oxygen) filter and high power may start to show structure with care.

NGC 6891 lies near the western border with Aquila. Found by Copeland in 1884, this planetary nebula lies around 1.5° southwest of a pair of 6th magnitude stars. The telescope will show a small blue/green elongated glow whilst high power may show an 11th magnitude central star.

NGC 7006 is a very remote globular cluster lying around 130,000 light years distant. At this distance, compare to omega Centauri at 17,000, it appears to be extra-galactic in nature. Found in the eastern section of Delphinus, there is very little obscuration from dust and gas. It appears fairly bright with a much brighter core, however the stars are unresolved, being 15th magnitude and fainter.

Our final deep sky object is NGC 6934, a globular cluster lying in the southern region of the constellation. Look around 1° northwest of a pair of unrelated 6th and 7th magnitude stars. It shows as a bright and large ball of suns with a brighter central region. A medium mirror sees it mottled whilst large mirrors may resolve individual faint stars.

Have a good sweep around Delphinus then perhaps drift over into nearby Aquila and enjoy its treasures.

Clear skies and good hunting ~ CosMos

Credits:

Albrecht Dürer, Riding a Dolphin, watercolor, circa. 1514