Gamma Delphini (γ² & γ¹ Delphini)
Coordinates, Gaia DR3 distance (115 ly), 8.9″ separation of K1 IV subgiant and F7 V dwarf, and observing guide for Gamma Delphini.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Combined apparent visual magnitude (V) | 3.87 mag | ± 0.01 mag | Johnson UBV photometry (γ² Del = 4.27 mag, γ¹ Del = 5.14 mag) | definitive | Hipparcos New Reduction Catalog |
| System distance (Gaia DR3) | 35.15 pc | ± 0.12 pc | Gaia DR3 astrometric parallax of γ¹ & γ² Del (28.45 ± 0.10 mas / 114.6 ly) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Visual γ²–γ¹ angular separation (2026 epoch) | 0.148 arcmin | ± 0.002 arcmin | WDS & Gaia DR3 astrometry (8.9 arcseconds at PA 265°; ~3,250-year orbit) | definitive | ESA Gaia Archive — Data Release 3 |
| Primary effective temperature (γ² Delphini) | 4930 K | ± 40 K | High-resolution spectroscopy (companion γ¹ Del = 6,290 ± 50 K) | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Gamma Delphini (Golden & Emerald Double Star) at RA 20h 46m 39.50s, Dec +16° 07′ 27.4″ within Delphinus, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Gamma Delphini (12 Delphini), marking the northeastern corner (the nose of the leaping Dolphin) of the compact diamond asterism known as 'Job's Coffin' in Delphinus, is one of the showpiece double stars of the summer and autumn sky. Shining at combined apparent magnitude 3.87 at a Gaia DR3 distance of 35.15 ± 0.12 parsecs (114.6 light-years), it was cataloged by James Bradley in 1755 and Friedrich Georg Wilhelm Struve as Struve 2727 (Σ2727).
The pair consists of two evolved stars ~2.5 billion years old orbiting their common center of mass every ~3,250 years along an eccentric path (semi-major axis ~330 AU): the brighter eastern component, Gamma² Delphini (magnitude 4.27), is a 1.72-solar-mass K1 IV orange-gold subgiant that has exhausted core hydrogen and swollen to 3.8 solar radii at 4,930 K, while the western component, Gamma¹ Delphini (magnitude 5.14), is a 1.57-solar-mass F7 V yellow-white turnoff star (2.1 solar radii, 6,290 K).
In the eyepiece, the juxtaposition of the 4,930 K golden subgiant beside the 6,290 K yellow-white dwarf triggers a famous physiological simultaneous-contrast effect on the human retina: while many observers see golden-amber and creamy white, others vividly perceive Gamma¹ Delphini as pale lime-green or aquamarine!
Practical Visual Observing Guide
- Look 10° northeast of Altair for the unmistakable four-star diamond of Delphinus; Gamma Delphini is the easternmost star of the diamond.
- Separated by 8.9 arcseconds due east-west (position angle 265°), Gamma Delphini splits crisply in any 50–80 mm telescope at 50×–100×.
- Right in the same low-power eyepiece field (14 arcminutes southwest of Gamma Delphini) sits Struve 2725 (Σ2725), a fainter 7.5- and 8.2-magnitude double star separated by 6.1 arcseconds—giving you a 'double double' field in Delphinus!
Catalog Cross-Identifications & Aliases
Common Aliases: γ Delphini · γ² & γ¹ Delphini · HD 197964 / HD 197963 · HIP 102532 · 12 Delphini
| Catalog Authority | Identifier |
|---|---|
| GAIADR3 | 1809644465314378752 |
| HIP | HIP 102532 |
| HD | HD 197964 |
| SIMBAD | * gam02 Del |
| WIKIDATA | Q13061 |
Related Objects, Comparisons & Guides
Albireo (Beta Cygni Color Double Star)
Coordinates, Gaia DR3 parallaxes of Beta Cygni A & B, 34.6″ angular separation, color contrast, and observing guide for Albireo in Cygnus.
Altair (Alpha Aquilae Rapid Rotator)
Coordinates, Hipparcos distance (16.73 ly), magnitude 0.76, 8.9-hour oblate spin imaged by CHARA, and observing guide for Altair in Aquila.
Epsilon Lyrae (The Double Double Star)
Coordinates, Gaia DR3 distance (160 ly), 208″ wide pair and 2.3″/2.4″ tight sub-pairs, and telescope resolution test guide for Epsilon Lyrae.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
Trigonometric Parallax, Parsecs & Gaia DR3
How trigonometric parallax (d_pc = 1 / p_arcsec), the distance modulus equation, Hipparcos, and Gaia DR3 microarcsecond astrometry measure cosmic distances.
Scientific Sources & Dataset Provenance
- ESA Gaia Archive — Data Release 3 (DR3 (2022-06-13)): Gaia Collaboration, Vallenari, A., et al. 2023, A&A, 674, A1 (Gaia Data Release 3) — European Space Agency / Gaia DPAC
- Hipparcos New Reduction Catalog (2007 New Reduction): van Leeuwen, F. 2007, A&A, 474, 653 (Validation of the new Hipparcos reduction) — ESA / van Leeuwen (2007)
- 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