Constellation Dolphin (Delphinus - Del)


If in the middle of summer we make observations of the starry sky, it is not difficult to come across three very small constellations, two of which are really right and which, once recognized, are very difficult to forget. Through the Stellarium website, we can see that the constellations of the Horse, the Dolphin and the Arrow are positioned near the constellation of the Eagle and the brilliant Altair, near that magnificent luminous track that is the Milky Way. Let's go and analyse them up close.



θ Del from 10 UA away

Thanks to Celestia we can see this class K3 star, from the distance adopted by me as standard, 10 UA, really bright and with an apparent diameter greater than 5°: always remember that from the distance of 10 UA (Saturn's distance from the Sun) our Sun appears very small, a little more than 3′, but always very bright.

Two stars of the Dolphin, α and β, have been baptized with strange names at first sight, respectively Sualocin and Rotanev: for the non enigmasters I will report the solution of the mystery at the end of the article...

Another star (ε Del) instead is called (I don't know by whom, I found the name on internet) Deneb Dulphim, the dolphin's tail, following a tradition of many constellations representing animals. As for the stars, there's nothing more to add to what little I reported: but now with the deep sky objects, our Dolphin will show all its beauty.

Deep sky objects

Let's start with a planetary nebula (NGC 6891) really suggestive: I remember that generally the photos I propose are almost always taken by the HST)


planetary nebula NGC 6891

Now we move on to two fantastic globular clusters, the first of which is NGC 6934

the globular cluster NGC 6934

while the other is NGC 7006

the globular cluster NGC 7006


Representation of the Dolphin

It's now time to see how the ancients represented this animal, starting from Hevelius

the Dolphin according to Hevelius

and then move on to Uranometry

the Dolphin according to Uranometry

only to end up with our beloved Stellarium...

the Dolphin according to Stellarium
they hide beautiful gem caskets I totally agree!
The sky is a source of wonder! Most of the time hidden...


The name, history and myth of Delfino


In India its auspicious stars were associated with porpoises; the Arabs, in ancient times, called them "precious stones". The quadrilateral of the main stars is called "Job's coffin" in English. For the Greeks it was the "sacred fish". According to Eratosthenes, Poseidon, god of the sea, was tired of his lonely life and thought he was looking for a wife.

He was enchanted by the beautiful Amphitrite, a sea nymph, one of the Nereids, who however did not seem at all interested in courtship. So it was that Neptune asked a dolphin for help, who managed to convince the nymph. In gratitude, Neptune placed the dolphin in the sky in the form of a constellation.

It's not the only legend, though. Another one - sung by Igino and Ovid, sees the dolphin as the animal that saved the musician of Lesbos Arion (a historical figure who lived at the turn of the 7th-6th centuries BC) from the waters of the ocean into which he was thrown by his crew. In practice, Arion had just won a musical competition full of prizes and was returning home when the crew threw the singer into the sea to grab the prizes. When the rescuer dolphin died, the animal was brought back to life and placed in the sky for merit. Apollo, who sent the dolphin into the sky, also wanted to save the musical instrument, the Lira...

The Curious Horse


Of this constellation we can say that it is really small and rather insignificant (but obviously no object in the sky is insignificant in the eyes of an enthusiast!): it has two stars (9 Equ and 3 Equ) just over 60 times the size of our Sun, while the star δ Equ is quite close to us, with a distance of 60 light years: compared to the astronomical distances of galaxies and black holes, this star is almost around the corner, but still very far away from the distances we are used to every day.


Among the galaxies in this small area of the sky, I show you NGC 7015, really beautiful.



The representation of Cavallino

In rapid succession, we see the representation of Hevelius

the Little Horse according to Hevelius

of Uranometry

the Horse according to Uranometry

and Stellarium

the Horse according to Stellarium

always showing the snout of a pony, very close to the snout of the winged horse Pegasus.

I conclude the analysis of this constellation adding that the star α Del is the only one to have a name, Kitalpha, which means part of the horse.

A curious arrow


Arrow stars comparison with other notes

In the diagram made as always with Illustrator, we see the red δ Sge and 13 Sge, class M2 and M4 with diameters respectively 177 and 166 times our yellow dwarf.

Remarkable are also β Sge and 10 Sge, two stars of spectral class G8 and G5 (therefore of the same family of the Sun), with diameters of 64 and 43 times our Sun, two monsters of the sky.

the Sun of 15 Aegis

In this constellation there is a star quite close to us (15 Sge, placed at 58 al): going to visit my friends Quindicinali I realized that our Sun, of just sixth magnitude, is in a zone of the sky poor of stars, but with two neighbors (prospectively) of respect, no less than Sirius and Altair, also weak, just of third magnitude.

10 UA delta Sagittae

Of the star δ Sge I show you the disturbing and imposing aspect from the distance of 10 UA: the star shines brightly with a diameter $superior$ to 8°: my Deltasgeian friends no longer know how to protect themselves from the brightness of their sun and the only solution they have found is to move to the dark side of their planet Moon, an area they call "the dark side of the moon"... what a fantasy!

The arrow... is always an arrow.

The representation of this constellation, both in antiquity and modernity, is quite obvious: for Hevelius it has a very long soaring

the Arrow according to Hevelius

while in the Uranometry it also has a central part, in addition to the tip and the tail.

the Arrow according to Uranometry

and finally, according to Stellarium, it's absolutely conventional

the Arrow according to Stellarium

A nice globular cluster

Our celestial arrow has inside it a globular cluster belonging to the Messier catalogue (M71) of which here we see a nice picture, always by HST

the M71 globular cluster

Visibility and mystery solving

These are summer constellations, clearly visible on the hottest nights of the year: at the usual time (9 p.m.) they are on the eastern horizon towards the end of June, culminating in the south, high on the horizon towards the end of September, while finally they are in the west at the beginning of December.

For those who are not passionate about puzzles, I suggest reading the names backwards: we will therefore get Nicolaus and Venator, the Latinisation of Nicola Cacciatore, the assistant of the astronomer Piazzi (discoverer of Ceres) in the compilation of a star catalogue.



Audio Video Constellation Dolphin (Delphinus - Del)
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