Constellations: Delphinus 'the Dolphin' Content from the guide to life, the universe and everything

Constellations: Delphinus 'the Dolphin'

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The shield of the Science, Mathematics and Engineering faculty of the h2g2 University.Constellations: Overview | Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Boötes | Caelum
Camelopardalis | Cancer | Canes Venatici | Canis Major | Canis Minor | Capricornus | Carina | Cassiopeia | Centaurus
Cepheus | Cetus | Chamæleon | Circinus | Columba | Coma Berenices | Corona Australis | Corona Borealis | Corvus
Crater | Crux | Cygnus | Delphinus | Dorado | Draco | Equuleus | Eridanus | Fornax | Gemini | Grus | Hercules | Horologium
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Puppis | Pyxis | Reticulum | Sagitta | Sagittarius | Scorpius | Sculptor | Scutum | Serpens | Sextans | Taurus
Telescopium | Triangulum | Triangulum Australe | Tucana | Ursa Major | Ursa Minor | Vela | Virgo | Volans | Vulpecula
The constellation Delphinus.
The happiness of the bee and the dolphin is to exist. For man it is to know that and to wonder at it.
– Jacques Yves Cousteau

Name:Delphinus (Latin 'dolphin')
Genitive:Delphini
Short form:Del
Area:189 sq deg
Co-ordinates1:Right Ascension 21h, Declination +10°
Origin:Ancient

Delphinus is a small northern group of stars, the 69th in order of area of the modern 88 internationally recognised constellations. It is bordered by Sagitta, Aquila, Aquarius, Equuleus, Pegasus and Vulpecula. What is noteworthy about Delphinus is that it actually resembles, when the stars are joined in the imagination, the creature it is supposed to depict - a dolphin jumping out of the sea.

There are no Messier objects in Delphinus, but there are some remarkable binary and multiple star systems, five extrasolar planets, a couple of planetary nebulae and two globular clusters, including Caldwell 42.

Mythology

There are different stories about the origins of the dolphin constellation. In one, Delphinus is the dolphin sent by the gods to save the drowning musician and poet Arion. He had been thrown overboard by sailors who were supposed to be giving him safe passage, so that they could keep his personal effects and considerable wealth. The gods had been listening to Arion's music earlier in the voyage, so witnessed the treachery taking place. Apollo was so moved by the plight of the gifted musician that he sent Delphinus to his aid.

Another version of the tale concerns Amphitrite, one of the the Nereids (sea-nymphs) being pursued by Poseidon. As she was trying to escape his attentions, a dolphin persuaded her to accept the sea god's marriage proposal. Poseidon was so grateful to the creature he placed the dolphin's image among the stars as a constellation.

Stars

The scientific star names are simple to understand (if you know your Greek alphabet). For example: the 'alpha' star means it is the brightest star in that constellation. The next brightest is designated 'beta' etc. Combined with the genitive name, this is known as the 'Bayer designation'. Some stars have proper names as well, for example, alpha Delphini is Sualocin. Others are known by their catalogue number.

Stars in Delphinus

That is the way the system is supposed to work, but sometimes the stars are variable, or when the cataloguing was undertaken the measurements were a little out. In this constellation, the fourth-magnitude beta star Rotanev is just a little brighter than the alpha star. The stars are not generally reset on charts to avoid confusion.

Star Table

StarDesignationName or
catalogue number
MagnitudeDistance
(light years2)
Spectral classification
and/or comments
β Delbeta DelRotanev+3.6110Multiple star system
α Delalpha DelSualocin+3.7170Multiple star system
ε Delepsilon DelDeneb el Delphinus
('tail of the dolphin')
+4.0 var490Blue-white giant
γ Delgamma Del12 Delphini+4.275Binary star system
δ Deldelta Del11 Delphini+4.4 var185White giant
ζ Delzeta Del4 Delphini+4.6125White giant
κ Delkappa Del7 Delphini+5.1100Yellow dwarf
η Deleta Del3 Delphini+5.4 var170White giant
ι Deliota Del5 Delphini+5.4177Binary star system

At just 75 light years distant, the fifth-magnitude yellow-white main sequence gamma1 and fourth-magnitude orange subgiant gamma2 make gamma Delphini a popular binary star system target for amateur stargazers.

The names Sualocin and Rotanev first appeared for alpha and beta Delphini in the 1814 Palermo Catalogue. By reversing the names to read Nicolaus Venator, you get the Latinised name of Niccolò Cacciatore, assistant to director Giuseppe Piazzi at the Palermo Astronomical Observatory. Did Cacciatore insert the names in the star catalogue behind his boss' back? According to Mazzaroth by Frances Rolleston, the Arabic word for swift (as the flow of water) is scalooin, and rotaneb (or rotaneu) means swiftly running (or even 'swimming'). So it is possible the names are not entirely coincidental. They could have been named in his honour by the director of the PAO and have nothing to do with Cacciatore's ego at all.

Nova Delphini 2013

On 14 August, 2013, Japanese amateur astronomer Koichi Itagaki was studying the Summer Triangle, an asterism (a shape made up by joining stars which is not a recognised constellation) coined by Sir Patrick Moore, when he noticed something unusual in this constellation. It seemed to have an extra star! After studying it with his telescope, he reported his finding and lo and behold, it turned out to be a nova, the sudden brightening of a star (in this case, by 11 magnitudes) due to an outburst. It has been catalogued Nova Delphini 2013 and it featured as Astronomy Picture of the Day on 16 August just two days after Koichi's discovery.

Job's Coffin

Interestingly, constellations are mentioned in The Bible:

The waters are hid as with a stone, and the face of the deep is frozen. Canst thou bind the sweet influences of Pleiades3, or loose the bands of Orion? Canst thou bring forth Mazzaroth4 in his season? Or canst thou guide Arcturus with his sons? Knowest thou the ordinances of Heaven? Canst thou set the dominion thereof in the Earth? Canst thou lift up thy voice to the clouds, that abundance of waters may cover thee?
Book of Job 38 vs 30-34

In Delphinus there is an asterism of four stars: alpha, beta, gamma and delta Delphini. It is known as 'Job's Coffin'.

New General Catalogue (NGC)

The NGC was compiled by John Louis Emil Dreyer (director of the Armagh Observatory from 1882 - 1916). Since the NGC catalogue was created, improved detection methods have uncovered other wondrous sights which are registered as IC (Index Catalogue), Sh (the Sharpless Catalogue), or the Caldwell Catalogue which was compiled by Sir Patrick Moore. There is a globular cluster, NGC 7006, in the constellation Delphinus which has the honour of being Caldwell 42 in Sir Patrick's catalogue.

NGC Table

CatalogueTypeMagnitudeDistance
(light years)
Remarks
NGC 6891Planetary nebula+10.77,200On border with Aquila
NGC 6905Planetary nebula+114,700Blue Flash Nebula
NGC 6934Globular cluster+8.748,000Discovered by William Herschel in 1785
NGC 7006Globular cluster+10.6113,000Caldwell 42

Extrasolar Planets

The methods used for the detection of extrasolar planetary systems have expanded greatly since the 1990s, and the techniques are being fine-tuned so that Earth-like planets can be discovered and studied. One method is OGLE, the Optical Gravitational Lensing Experiment which makes observations at the Las Campanas Observatory, Chile, using a second-generation CCD 8kMOSAIC camera. OGLE regularly monitors 130 million stars in the galactic bulge of the Milky Way.

Extrasolar Planets in Delphinus

Four exoplanets had been found in the constellation Delphinus up to 2008; the first was discovered in 1998. The figures given in the table below are the length of the planet's orbital period around its parent star, which we know of as a year. The mass of the extrasolar planet is compared with that of Jupiter, our solar system's largest planet, known to astronomers as the 'Jovian scale'.

Extrasolar Planets Table

Star name or
catalogue number
Planet
catalogue number
Planet mass
(Jovian scale)
Orbital period
(Earth days)
Year of discoveryComments
HD 195019 AHD 195019 A b3.718.21998Hot superjovian
WASP-2WASP-2 b0.92.152006Hot Jupiter
HD 196885 AHD 196885 A b31,3502007Superjovian
18 Del18 Del b10.3993.32008Superjovian
HAT-P-23HAT-P-23 b21.22010Superjovian

Delphinus in Modern Culture

  • St Delphinus was the Bishop of Bordeaux, France, whose feast day is 24 December.

  • The Delphinus Chronicles is a 2002 novel by Richard G Roane.

  • Delphinus Care is a residential home in Essex for people aged between 12 and 18 who have a diagnosed learning disability.

1Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (−) for southern ones.2A light year is the distance light travels in one year, roughly 5.88 trillion miles or 9.46 trillion km.3M45 in Taurus.4The Hebrew word Mazzaroth means 'constellations'.

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