NGC 6826 is a magnitude +8.8 planetary nebula located in northeastern Cygnus. It's a compact object that blinks on and off when observed, hence the name Blinking Planetary. Most planetary nebulae exhibit this type of behaviour but with NGC 6826 it's particularly obvious. When you look directly at the central star the nebula tends to fade away but glancing towards the edges - using averted vision - it suddenly re-appears. Switching back and forth rapidly between averted and direct vision causes the nebula to dramatically blink on and off.
NGC 6826 was discovered by William Herschel on Sep 6, 1793. It's number 15 in the Caldwell catalogue and is best seen from northern locations during the months of June, July, August.
The Blinking Planetary is positioned 11 degrees northwest of Deneb (α Cyg - mag. +1.25) and 1.35 degrees east of theta Cyg (θ Cyg - mag. +4.5). It can be seen with popular 7x50 or 10x50 binoculars, although it appears only like a dim star. Through a small scope, such as an 80mm (3.1-inch) refractor, NGC 6826 appears evenly illuminated but small. The main section of the nebula spans just 27 by 24 arc seconds and is therefore smaller than the apparent diameter of the planet Jupiter. However, it responds well to power and the magnitude +10.6 central star is easily visible. Within a degree of NGC 6826 is double star 16 Cyg, consisting of two white 6th magnitude stars.
Through a 200mm (8-inch) scope NGC 6826 appears bright and blue-green in colour. High magnifications of the order of 250x display an elongated shelled structure. With direct vision the central star is prominent but averted vision brings out the nebula and at the same time reducing the dominance of the star. A nebula filter like an Olll helps increase the visibility of the disk but tends to dim the central star. With large backyard scopes the planetary is well defined and the blinking effect obvious.
NGC 6826 is estimated to be 2,200 light-years distant. There is deal of uncertainty about this figure and it could be as close as 2,000 light-years or as far away as 5,000 light-years. The Hubble Space Telescope spectacularly imaged it revealing two bright patches on either side, which are known as Fast Low-Ionization Emission Regions, or FLIERS. They appear to be relatively young, moving outwards at supersonic speeds.
NGC 6826 Data Table
|Object Type||Planetary Nebula|
|Distance (light-years)||2,000 -> 5,000|
|RA (J2000)||19h 44m 48s|
|DEC (J2000)||50d 31m 31s|
|Apparent Size (arc secs)||27 x 24 (main section)|
|Radius (light-years)||0.25 -> 0.65|
|Notable Features||Has a bright central star at mag. +10.6|