What kind of star is Sadr?
Sadr, catalogued as Gamma Cygni (γ Cyg), appears in the official constellation Cygnus. Its apparent visual magnitude is 2.23, while its estimated distance is roughly 1,800 light-years; parallax uncertainty is large. Astronomers classify the object as F8 Ib. These labels describe temperature, luminosity class or system components; they should not be read as a claim that every naked-eye point is a single isolated star.
Gamma Cygni is an F8 supergiant whose small SIMBAD parallax corresponds to roughly 1,800 light-years, but that value is highly sensitive to astrometric uncertainty. The star is many times the Sun's mass and tens of thousands of times as luminous, with an expanded atmosphere showing pulsational and wind-related variability. Sadr appears superimposed on the IC 1318 emission-nebula complex, often called the Gamma Cygni Nebula. Distance estimates indicate that the star and much of the ionized gas may occupy the same broad star-forming region, but photographs combine structures at different depths and should not imply that Sadr alone powers every visible arc. Dense Milky Way dust creates the dark lanes dividing the red nebula into distinctive lobes.
The coordinate pair RA 20h 22m 13.70s, Dec +40° 15′ 24.0″ fixes the object's direction on the celestial sphere for the J2000 reference epoch. Right ascension works like celestial longitude measured in hours, while declination works like latitude north or south of the celestial equator. Proper motion and improved measurements can refine catalogue positions, but these coordinates are sufficiently precise for a finder chart or planetarium search.
Sadr data at a glance
| Proper name | Sadr | Catalogue designation | Gamma Cygni (γ Cyg) |
|---|---|---|---|
| Constellation | Cygnus | Apparent magnitude | 2.23 |
| Spectral or system type | F8 Ib | Estimated distance | roughly 1,800 light-years; parallax uncertainty is large |
| Right ascension (J2000) | 20h 22m 13.70s | Declination (J2000) | +40° 15′ 24.0″ |
Values are rounded for an observer-friendly overview. Consult the linked SIMBAD record for component-level identifiers, bibliography, measurement provenance and newer catalogue values.
The name Sadr
From Arabic ṣadr al-dajājah, “the breast of the hen,” describing its central place in the Swan or Hen figure.
The Arabic name identifies the bird's breast, exactly where the arms of the Northern Cross intersect. This central geometry made Sadr an enduring navigational marker. Modern narrowband astrophotography has made its surrounding nebula far more familiar, sometimes causing the extended complex to be misleadingly treated as if it were simply the star's personal shell. Older atlases emphasized the Swan's anatomy; modern images instead make Sadr a gateway to understanding the layered Cygnus X region.
Modern professional catalogues retain identifiers such as the Bayer designation alongside a proper name. The International Astronomical Union standardizes which name belongs to which component—an important distinction for systems whose combined light looks like one star from Earth.
How to find Sadr
Find the Summer Triangle, then trace Cygnus from Deneb toward Albireo. Sadr is the central star where the Cross's wings meet. Binoculars show an exceptionally rich field; the nebula requires a dark sky, wide-field telescope and often a UHC filter or long-exposure imaging.
A northern star, circumpolar from high latitudes and best on summer and autumn evenings. Visibility on a particular night still depends on latitude, season, time, horizon obstructions, weather and local light pollution. Use the interactive atlas below to check the surrounding field before observing.
Observation checklist
- Best from June through November evenings.
- Use binoculars first for the rich surrounding star clouds.
- A UHC filter can improve parts of IC 1318 under dark skies.
- Photographic red nebulosity is much fainter visually than images suggest.
Interesting facts about Sadr
- Sadr marks the centre of the Northern Cross.
- It is a distant yellow-white supergiant.
- IC 1318 surrounds it in projection and broad physical region.
- Dark dust lanes divide the emission complex.
- Its distance and luminosity remain uncertain because the parallax is small.
Continue from Sadr into the night sky
Use the Cygnus constellation guide to place this star within its larger pattern. When you are ready to observe, compare dark-sky places, find a nearby observatory, or follow our practical guide to finding a star in the night sky. Symbolically registered names are kept separately in the searchable Star-Register catalogue.
Sources and further reading
Measurements are rounded for readability. Multiple systems, variable stars and distant supergiants can have component-specific or model-dependent values. Survey panels show photographic sky fields, not the physical surface of the star.