Blinking Planetary Nebula (NGC 6826 / Caldwell 15)
Coordinates, Gaia DR3 distance (1.30 kpc), magnitude 8.8, rod/cone averted-vision blinking illusion, and observing guide for NGC 6826 in Cygnus.
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 |
|---|---|---|---|---|---|
| Integrated visual magnitude (V) | 8.8 mag | ± 0.1 mag | Integrated CCD aperture photometry | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric distance | 4240 ly | ± 130 ly | Gaia DR3 trigonometric parallax of 10.6-mag central star (1.30 ± 0.04 kpc) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Bright inner oval diameter | 0.45 arcmin | ± 0.05 arcmin | Main ionized shell (27″ × 24″; outer AGB halo spans 2.2′) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Blinking Planetary (NGC 6826 in Cygnus) at RA 19h 44m 48.15s, Dec +50° 31′ 30.3″ within Cygnus, 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
The Blinking Planetary (NGC 6826, Caldwell 15) is a famous 27 × 24 arcsecond planetary nebula located 4,240 light-years (1.30 ± 0.04 kiloparsecs) away in northern Cygnus, discovered by William Herschel on September 6, 1793. Its celebrated 'blinking' behavior is not an astrophysical pulsation at all, but a physiological quirk of the human retina: when you stare directly at the 10.6-magnitude central star (HD 186924) using color-sensitive foveal cone cells, the glare of the star overwhelms the surrounding 8.8-magnitude nebula so the shell seems to vanish; when you shift to averted vision a few degrees to the side, your hypersensitive peripheral rod cells instantly cause the bright green nebula to 'blink' back on.
In Hubble Space Telescope images, NGC 6826 is the textbook showcase for 'FLIERs' (Fast Low-Ionization Emission Regions)—two bright crimson knots of singly ionized nitrogen ([N II]) sitting at opposite ends of the nebula's major axis like ruby wingtips.
Because NGC 6826 fell directly inside the primary field of view of NASA's Kepler space telescope, continuous ultra-precise photometry of its 46,000 K O3f central star uncovered stochastic hours-long brightness variations driven by clumps in its fast radiation-driven stellar wind.
Practical Visual Observing Guide
- Easy to locate just 0.5° east of the wide, colorful binocular double star 16 Cygni (a famous pair of 6th-magnitude solar-twin stars separated by 39″, one of which hosts exoplanet 16 Cygni Bb).
- To trigger the 'blinking' illusion best, use an 80–150 mm telescope at medium magnification (80×–140×) WITHOUT any nebula filter, alternating rapidly between direct fixation on the 10.6-mag central star and averted vision.
- At higher power (200×–300×) in a 200 mm+ aperture, look for the brighter inner elliptical ring and the two tiny polar condensations (FLIERs) at the southeast and northwest tips.
Catalog Cross-Identifications & Aliases
Common Aliases: NGC 6826 · Blinking Planetary · Blinking Nebula · Caldwell 15
| Catalog Authority | Identifier |
|---|---|
| NGC | NGC 6826 |
| SIMBAD | NGC 6826 |
| WIKIDATA | Q488509 |
Related Objects, Comparisons & Guides
Eskimo Nebula (NGC 2392 / Clownface Nebula)
Coordinates, Gaia DR3 distance (1.76 kpc), magnitude 9.1, radial cometary filaments, X-ray binary core, and observing guide for NGC 2392 in Gemini.
Blue Snowball Nebula (NGC 7662 in Andromeda)
Coordinates, Gaia DR3 distance (1.76 kpc), magnitude 8.3, vivid O-III/He-II blue-green excitation, and observing guide for NGC 7662 in Andromeda.
Ring Nebula (Messier 57 in Lyra)
Coordinates, Gaia DR3 central star distance (787 pc), magnitude 8.8, and telescope observing guide for the Ring Nebula (M57) in Lyra.
Surface Brightness & Extended Objects Guide
Why surface brightness (mag/arcsec²) governs nebula and galaxy visibility more than integrated magnitude, and how exit pupil controls eyepiece contrast.
Apparent vs Absolute Magnitude Explained
Understand the logarithmic Pogson astronomical magnitude scale, apparent visual magnitude (m), absolute magnitude (M at 10 parsecs), and bolometric corrections.
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
- Revised New General Catalogue and Index Catalogue (RNGC/IC) (2024/2026 edition): Steinicke, W. 2010, Observing and Cataloguing Nebulae and Star Clusters (Cambridge Univ. Press); Verga, M. OpenNGC (CC-BY-SA 4.0 / data tables) — Wolfgang Steinicke / OpenNGC
- 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