While the Milky Way along the backbone of the constellation Cygnus, the Swan, offers many fine targets for stargazers, the wings of the constellation are also well worth exploring, especially in the months of July through October when the constellation lies near the meridian. In this short tour, let’s tiptoe through the western wing of the Swan and inspect the remarkable Blinking Planetary, NGC 6826, and a few more intriguing deep-sky objects.
Before we get to the Blinking Planetary, let’s look at the brightest star in this part of the sky. It’s δ (delta) Cygni, a 3rd magnitude triple star system about 165 light years away. Such a bright star in a prominent part of the sky deserves a proper name, but most star maps just label it δ Cygni, though some call it Rukh or Al-Fawari. Future generations will surely assign another name to this star. When the wobbling Earth directs its axis towards δ Cygni in a little more than 9,200 years, it will be called, for a time, the North Star.
Have a look at the star with your telescope and you’ll see the main 3rd-magnitude component as a blue-white gem. The bone-white 6th-magnitude companion lies about 2.4″ away, which makes it challenging to discern in unsteady sky. You’ll need 75x or so to split this pair in a small telescope. The much fainter red dwarf companion shines at 12th magnitude and is very hard to pick out from the background stars.
OK, now let’s get to the Blinking Planetary. Cataloged as NGC 6826, it’s just southeast of the star iota (ι) Cygni, and just west of a line extended from kappa (κ) to iota (ι) with a length equal to the distance between the two stars. The 9th-magnitude planetary is fairly small, just 25″ in apparent diameter, so it appears nearly star-like at 50x. You can determine if you have indeed found the nebula by increasing magnification to enlarge the disk. At 120x or more, the nebula will reveal an obviously oval shape and a subtle blue-green color. The 10th-magnitude central star of NGC 6826 is quite obvious in a small telescope. This star is generating the nebula as it casts off its outer layers from its blazing hot central core.
The video below shows you the nebula through an image intensifier and gives you an idea of what it looks like at high magnification.
The Blinking Planetary is an object that most dramatically demonstrates the effect of averted vision. Stare directly at this blue-green planetary nebula for several seconds and you see only the central star. Look slightly to the side and the faint nebula around the star appears suddenly. When you switch from straight on to averted vision, the nebula appears to blink on and off. It’s darned impressive. Using a nebula filter (such as a UHC or OIII filter) increases the contrast of the nebula against the background sky, but ruins the blinking effect.
If you’re hungry for more stargazing, look for the lovely little open star cluster NGC 6811. It’s just west of the line between δ Cyg and ι Cyg and much closer to the former. The little cluster is most fascinating for the assortment of shapes it resembles. Some say it looks like a smoke ring, some say it resembles the Liberty Bell, and others see Nefertiti’s headpiece, for example. Crank your telescope up to a moderate magnification around 50-80x and observe the cluster closely and carefully. What shape do you see?
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