OBSERVER’S CHALLENGE* – AUGUST, 2022
by Glenn Chaple
NGC 6772 Planetary Nebula in Aquila (Magnitude 12.7; Size 70” X 56”)
The July Observer’s Challenge featured the bright planetary nebula NGC 6210 in Hercules. This month, we visit another planetary nebula- one that, to put it bluntly, isn’t so bright. NGC 6772 is about the same size as M57, the Ring Nebula (70” X 56” to 86” X 62”), but is 4 magnitudes fainter (12.7 to 8.8). To see it visually, you’ll need a dark sky, reasonably large aperture scope, and (highly recommended) a nebula filter.
NGC 6772 is located in the southwest corner of Aquila at 2000.0 coordinates RA 19h14m36.4s, Dec -2o42’25.0”. Star-hoppers can find their way here by beginning 3 degrees southwest at 3rd magnitude lambda (λ) Aquilae (see Finder Chart B).
William Herschel may have overlooked NGC 6210, but his capable eye spotted NGC 6772 on the night of July 21, 1784. He described it as “very faint, round, nearly of equal light throughout, about 1’ in diameter, In the midst of numberless stars of the Milky Way,”
This planetary nebula proved to be a challenge when I tackled it on the night of June 25, 2022, with a 10-inch f/5 reflector. A limiting naked eye magnitude of 5 didn’t help. I was unable to see anything with an unfiltered view, Placing an O-III filter into a 13mm eyepiece brought out an extremely elusive roundish glow that I could only detect with averted vision. As Herschel had noted 238 years earlier, it was immersed in a field littered with faint stars.
Sources ascribe a distance of 4000-4200 light years to this planetary. Its true diameter may be in the order of 1.5 light years.
NGC6772 Finder Charts
Chart created using the AAVSO’s Variable Star Plotter (VSP). The location of NGC 6772 is marked with a crosshair. Numbers are stellar magnitudes, decimals omitted. The 3.4 magnitude star is lambda (λ) Aquilae. Stars plotted to 10th magnitude. North is up in this 3.5 X 3.5 degree field.
NGC 6772 Images
Image by Mario Motta, MD (ATMoB) taken with H alpha, S2, and O3 filters 1 hour each. With 32 inch scope, ASI 6200 camera.
Sketch by Glenn Chaple (ATMoB)