Delphinus
What is Delphinus?
Constellations· Summer–autumn evenings (N) · tiny diamond. A small dolphin beside the summer Milky Way, just east of Altair. Its crisp diamond of four stars is easy to find again once you have learned it.
📍 Visible from where you are right now — computed in your browser
Stars of the figure
| Star | Magnitude |
|---|---|
| Rotanev | 3.6 |
| Sualocin | 3.8 |
| Aldulfin | 4.0 |
| Gamma Delphini | 4.3 |
The 4 brightest of the 5 stars used in the figure (5 lines). Lower magnitude means brighter.
Constellation basics
| Season | summer–autumn evenings (N) |
|---|---|
| Brightest star | Rotanev (β, 3.6) |
| How to find | small diamond east of Altair |
| Area rank | 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
The new star that rose in Delphinus in 2013
On 14 August 2013 the Japanese amateur astronomer Koichi Itagaki discovered a star in Delphinus where none had been seen before. Named Nova Delphini 2013, it brightened two days later to magnitude 4.3, visible to the naked eye. It sat near the little diamond beside the Summer Triangle, so it was easy to find, and many people saw the new star for themselves.
A nova is not a newborn star. It happens when gas from a companion piles up on a small, dense white dwarf until it explodes on the surface, making the star flare up for a while. This nova left an important scientific record: beryllium-7 was found in the gas blown out by the explosion. Over time, beryllium-7 turns into lithium.
The observation became the first direct evidence that nova explosions make lithium and spread it into space, the same element used in batteries. Scientists had long predicted that novae were one of the sources of the universe's lithium, and the proof came from this small constellation. The star has since faded again and can be seen only through a telescope.
The constellation in depth
Delphinus is one of the 48 constellations listed by the ancient astronomer Ptolemy. In Greek myth it is the dolphin that persuaded the sea nymph Amphitrite to marry Poseidon, god of the sea. Another story makes it the dolphin that carried the poet Arion to safety after he leapt from a pirate ship.
The names of its two brightest stars, Sualocin and Rotanev, hide a joke. Read backwards, they spell Nicolaus Venator, the Latin form of the name of Niccolò Cacciatore, an assistant at Palermo Observatory in Italy in the 19th century. He is believed to have slipped his own name into a star catalogue this way.
In East Asia the diamond was a completely different picture. Old Chinese star maps saw these stars as a gourd hanging from a vine, called Hugua, and the stars below were given a name meaning ‘rotten gourd’. From the same four stars, Greece imagined a dolphin from the sea and East Asia a gourd from the garden.
On evenings from July to October, first find bright Altair in the south. About 15 degrees to its left (east), roughly one and a half fists at arm's length, lies the small diamond. All four stars are around 4th magnitude, so the shape survives city skies. Set the Sky view to a summer evening and zoom in beside Altair to see the diamond and its tail star.
Frequently asked
- When can I see Delphinus?
- Delphinus is best seen in summer–autumn evenings (N).
- How do I find Delphinus?
- To find Delphinus, look for small diamond east of Altair.
- What is the brightest star in Delphinus?
- The brightest star in Delphinus is Rotanev, at magnitude 3.6.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.