Delphinus (The Dolphin) Constellation Guide
Delphinus IAU constellation (189 sq deg, rank 69): September diamond asterism ('Job's Coffin') east of Altair, led by Rotanev (+3.64) and Gamma Del.
Sky Navigation & Astrophysical Context
Leaping just east of the Summer Triangle across 189 square degrees of the northern sky, Delphinus is one of the most charming and instantly recognizable miniature constellations from Ptolemy's Almagest. Its four head stars—Sualocin (Alpha Delphini, +3.77), Rotanev (Beta Delphini, +3.64), Gamma Delphini (+3.90 combined), and Delta Delphini (+4.43)—form a tight 2°-wide diamond lozenge known since the 19th century as 'Job's Coffin,' with Epsilon Delphini (Aldulfin, +4.03) extending southwestward as the Dolphin's tail.
The curious proper names Sualocin and Rotanev originated as an astronomical riddle in the 1814 Palermo Star Catalogue: British astronomer Thomas Webb discovered in 1859 that spelled backward, they read 'Nicolaus Venator,' the Latinized name of Niccolò Cacciatore, assistant and successor to Giuseppe Piazzi at the Palermo Observatory.
At the northeastern nose of the diamond shines Gamma Delphini, one of the finest showcase double stars in the northern sky (+4.27 K1 IV orange-gold subgiant and +5.14 F7 V yellow-white dwarf separated by 9.2 arcseconds), while southern and eastern Delphinus contain the remote globular clusters NGC 6934 and NGC 7006 and the blue-green planetary nebula NGC 6891.
Equatorial Center Position & Transit Altitude
Delphinus is centered near Right Ascension 20h 41m 24s, Declination +11° 40′ 12″ (The Dolphin).
Practical Star-Hopping & Observing Tips
- Look 12° northeast of brilliant Altair (Alpha Aquilae) to spot the miniature kite diamond of Job's Coffin and its tail star Epsilon Delphini.
- Point any 60 mm+ telescope at Gamma Delphini (the eastern tip of the diamond) at 60×–100× to resolve its golden and pale yellow-green components.
- Sweep 4° south of Epsilon Delphini to find the 9th-magnitude globular cluster NGC 6934.
Notable Celestial Objects in & Near Delphinus
| Object | Family | Classification | RA (J2000) | Dec (J2000) | Min. Instrument |
|---|---|---|---|---|---|
| Dumbbell Nebula (Messier 27 in Vulpecula) | nebulae | Planetary nebula (bipolar lobe system viewed equator-on) | 19h 59m 36.34s | +22° 43′ 16.1″ | 7×50 binoculars |
| Altair (Alpha Aquilae Rapid Rotator) | stars | Rapidly rotating A-type main-sequence star (Delta Scuti variable) | 19h 50m 47.00s | +08° 52′ 06.0″ | Naked eye |
| Gamma Delphini (Golden & Emerald Double Star) | multiple-stars | Physical visual binary of a K1 IV orange subgiant and an F7 V yellow-white dwarf | 20h 46m 39.50s | +16° 07′ 27.4″ | Naked eye; any 50–60 mm telescope at 50×+ splits the 8.9″ pair |
Scientific Sources Cited
- IAU Official Constellation Boundaries & Designations (IAU 88 Recognized Constellations): Delporte, E. 1930, Délimitation scientifique des constellations (IAU / Cambridge University Press) — International Astronomical Union (IAU)
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg