Key Takeaways:
- The planetary nebula NGC 6781, located in the constellation Aquila, is observable despite the constellation's relatively low density of prominent celestial objects.
- NGC 6781 is characterized as a near-perfect, expanding gas bubble approximately 2 light-years in diameter, resulting from the death of a Sun-like star.
- Observations through a 6-inch telescope reveal an irregular, oval-shaped nebula with a darker center and potential for discerning small dark blotches under favorable atmospheric conditions.
- Larger telescopes (16-inch or greater) allow for observation of detailed ring structure within NGC 6781, including a brighter southern rim and a fainter, broken northern edge; the central white dwarf star may also be visible under exceptional viewing conditions.
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.
