The constellation Delphinus

Characteristics

Other names / Symbolism

Dolphin

Hemisphere

Northern hemisphere

Visibility

March - January

Area

189 deg²

Brightest star

Rotanev (HIP number 101769)

Specialties

Globular clusters, planetary nebulae

The Delphinus, Latin for dolphin, is one of the 48 classical constellations of antiquity named by the Greco-Roman astronomer Claudius Ptolemy. It is one of the smallest constellations in the night sky, yet still very prominent. In the area lie a couple of exciting deep-sky objects.

Hemisphere, visibility, and area

The Delphinus constellation lies in the northern sky near the celestial equator. As a result, it is visible nearly everywhere. It can be observed from all regions in the northern hemisphere. South of the equator, it is visible up to latitude 70. Therefore, it can be seen until the southern polar circle and a little beyond. Only in Antarctica is it not showing.

The constellation can be observed nearly all year round, as it is visible in the night sky from March to January. Different months are optimal for observation, depending on the region. In Central Europe, Canada, and the US, especially the summer months are suitable.

Delphinus is located slightly below the Summer Triangle, which consists of stars from the constellations Cygnus, Lyra, and Aquila.

In the vicinity are also the constellations Vulpecula and Sagitta in the north. To the northwest is Aquila, while Aquarius and Equuleus are to the south. Pegasus borders the constellation in the east.

Although it only covers an area of about 189 square degrees, it is easily identifiable in the night sky due to its distinctive shape. The visualization of the constellation consists of four stars arranged in a diamond shape, which form a trail of stars behind them. The diamond or rhombus represents the body of the jumping dolphin, while the star trail pointing downward represents the tail.

The two brightest stars of Delphinus are named Rotanev (Latin: β Delphini, Beta Delphini) and Sualocin (Latin: α Delphini, Alpha Delphini). Their names have a peculiar feature, as they spell "Nicolaus Venator" when read backward. That is the Latin form of the Italian astronomer Niccolò Cacciatore, who introduced the names to the star catalog in 1814.

Specialties in the constellation

Within the Delphinus constellation are two small globular clusters, NGC 6934 and NGC 7006.

While NGC 6934 is about 50,000 light-years away from earth and can be seen with a small telescope starting at 3 inches, the second globular cluster, NGC 7006, requires a telescope of at least 8 inches in size. This is because this cluster is located at a distance of over 135,000 light-years, making it one of the most distant globular clusters in the Milky Way.

In addition, there are two planetary nebulae within the constellation. NGC 6905, also known as the Blue Flash Nebula, is one of them. It was discovered by the German-British astronomer William Herschel in September 1784 and is located around 3,000 light-years away from earth.

The other planetary nebula has the catalog number NGC 6891. It was discovered by the Scottish astronomer Ralph Copeland in September 1884. On images captured by the Hubble Space Telescope, it appears as a bluish nebula spot.

Mythology

There are two different versions of the origin of the Delphinus constellation. Both refer to Greek mythology.

The first story is about the sea god Poseidon, who fell in love with Amphitrite, a daughter of the Titan Nereus. While Amphitrite's appearance enchanted Poseidon, she did not reciprocate his feelings and fled to her sisters.

In desperation, Poseidon sent messengers to Amphitrite to try and convince her to become his wife. Among them was a dolphin, who won Amphitrite's trust with his charm and persuaded her to become Poseidon's wife.

In gratitude, Poseidon placed the dolphin in the night sky as a constellation.

The second interpretation is about the famous musician Arion, who traveled the world giving concerts and carrying a lot of money with him.

When the sailors of his ship found out about this, they wanted to rob him and throw him overboard. However, they allowed him to sing a last song before his supposed death. His singing attracted dolphins, safely bringing him to the shore, where he could get the sailors to justice.

To commemorate this event, a dolphin was placed in the sky.