Thursday, October 25, 2012

A pair of planetary nebulae in Aquila

While I was observing the periodic comet 168/P Hergenrother during it's apparently short lived outburst, I also looked at deep sky objects as well. Sky conditions were poor but I still managed to see a good many old standbys as well as a few new objects along the way. Two objects I have observed before with my 10-inch F/4.5 Dob were the Aquila planetary nebulae NGC-6772 and NGC-6778. This time I brought the 15-inch to bear on them to see if there was anything different about these objects through the larger telescope.
 

NGC-6772 turned out to be more interesting through the 15-inch Dob than when I looked at it the last time with my 10-inch. Unlike the oblong faint patch of light seen through the 10-inch, some visible structure appeared, in the form of a darker central zone and brighter regions along the long sides of the nebula. No central star was evident, evidently its either very faint, hidden by the glow of the surrounding nebula or both. The poor skies that night and the proximity to my city meant it was very faint without a nebula filter, but when an O-III filter was used it became far easier to see. Averted vision definitely helped here. This is a planetary nebula for folks who venture out to dark sites, no doubt it would show up well through an 8 or 10-inch telescope if the skies are very dark given it's overall listed magnitude is about 14. Realistically, I would say it's closer to magnitude 13 with an apparent size of about one arc-minute along its long axis. For users of larger telescopes, it is a very nice planetary nebula.

NGC-6778 is three times smaller in apparent size with a diameter of some 20 arc-seconds, and listed as a full magnitude brighter than NGC-6772. As such it penetrates light pollution and haze much more easily than it's larger and fainter counterpart. As before I experimented with viewing it with and without an O-III filter, and preferred the filtered view. It was still quite obvious among the dense star fields without it. Again no obvious central star was seen, but I did see a roundish, somewhat ill defined and irregular disk. Other than that, it seemed featureless. The high surface brightness actually allowed me to find it from home with my 10-inch, and thus the view I got was similar to what I recall seeing through the smaller telescope.

Among other objects I observed was an intriguing collection of galaxies in Pegasus. I didn't get to make any sketches of them before the heavy dewing started, but I did look them over. Since I am going to the Deep South Regional Stargaze this year, I am going to give them a closer look and make sketches with the 15-inch Dob from skies far darker than anything I can find in my local area. That is assuming of course the weather co-operates, an iffy thing here on the Gulf Coast with hurricanes sometimes striking my area even as late as December. The Sky Commanders I have added to that telescope work magnificently and make observing very faint objects a lot more rewarding. While I can star hop to any thing on a chart, it is nice to have some help looking for those 14th magnitude faint fuzzies, and something that can tell you which one you are looking at.

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