Key Takeaways:
- The planetary nebula NGC 6781, located in the constellation Aquila, is observable near Delta Aquilae and possesses a magnitude of 11.4 and an apparent diameter of 109 arcseconds.
- NGC 6781 is characterized as an expanding, approximately 2 light-year diameter, gas bubble expelled from a deceased, Sun-like star, undergoing decomposition by energetic photons from nearby stars.
- Observations through a 6-inch telescope reveal a soft, irregular, oval-shaped nebula with a darker center and potential for discerning subtle dark blotches under optimal seeing conditions.
- Larger telescopes (16-inch or greater) reveal a brighter southern rim and a broken, fading northern edge of the ring structure; a magnitude 16.2 central white dwarf star may be detectable under exceptional conditions with the use of nebula or OIII filters.
Although Aquila ranks 22nd in size among the 88 constellations, it contains no Messier objects or emission nebulae and few bright star clusters. Still, you’ll want to point your telescope 3.8° north-northwest of magnitude 3.4 Delta Aquilae to observe the wonderful planetary nebula NGC 6781. It glows at magnitude 11.4 and has a diameter of 109″.
NGC 6781 is an almost perfect bubble of gas cast off by a single, formerly Sun-like, star that has died. The bubble continues to expand; it measures some 2 light-years across. Energetic photons from nearby bright stars decompose the gas bubble. A similar process occurs within the Eagle Nebula (M16) in the constellation Serpens.
Through an 6-inch telescope at a magnification of 100x, NGC 6781 stands out well against a rich, star-filled background. The disk appears soft, irregular, and oval-shaped with a slightly darker center. If the seeing at your observing site is good, look for small, dark blotches over NGC 6781’s face.
If you’re able to observe this planetary through a 16-inch scope, lucky you will see lots of structure in NGC 6781’s thick ring. This feature’s southern rim appears brightest. The northern edge is broken and gradually fades into the background. To see the ring best, use a nebula or an OIII filter. Through this size or larger telescope, you might detect the central star, a bluish white dwarf, which glows weakly at magnitude 16.2 if your sky conditions are excellent.
