NGC 6891
Planetary Nebula in constellation Delphinus
From Wikipedia, the free encyclopedia
NGC 6891 is a bright, asymmetrical planetary nebula located in the northern constellation of Delphinus.[4][5][6] It was discovered on 22 September 1884, by Scottish astronomer Ralph Copeland, who observed it using visual spectroscopy with a 6.1-inch refractor at the Dun Echt Observatory in Aberdeen, Scotland.[7][1]
| Nebula | |
|---|---|
| Planetary nebula | |
Hubble Space Telescope image of NGC 6891 | |
| Observation data: J2000.0 epoch | |
| Right ascension | 20h 15m 08.84s[1] |
| Declination | +12° 42′ 15.6″[1] |
| Distance | 12,400[2] ly |
| Apparent magnitude (V) | 12.51±0.23[3] |
| Constellation | Delphinus |
| Designations | PN G054.1-12.1, PK 54-12.1, IRAS 20127+1233[1] |
Characteristics
NGC 6891 displays a triple-shell structure, consisting of a bright inner nebula, an attached intermediate shell, and a detached outer halo.[8] High-resolution imaging reveals filaments, knots, and intricate details in the interior surrounding the central white dwarf star named HD 192563, along with at least two ellipsoidal shells oriented differently and a spherical outer halo expanding faster than the inner regions.[9] The bright optical regions have an apparent diameter of approximately 15 arcseconds.[7] The nebula shows evidence of multiple mass ejection episodes from its progenitor star.[8][4]
Observation
NGC 6891 has an apparent visual magnitude of around 10.5 to 12 and appears as a small, bluish disc in amateur telescopes of 6 inches (150 mm) aperture or larger, with the central star faintly visible under good conditions.[3] It lies near the celestial equator in Delphinus and is observable from both hemispheres.[6] The nebula has been imaged in detail by the Hubble Space Telescope, contributing to studies of planetary nebula structure, formation, evolution, and distance determination.[4]