While at the Black Forest Star Party this past September, John Causland challenged me to track down some relatively obscure planetary nebulae that you may wish to check out for yourself. They are NGCs 6803, 6804, and 6807, all within a few degrees of one another in Aquila. Now. I know that it’s early fall, and Aquila (the Eagle) is normally thought of as a summer constellation, but it’s still more than high enough in the sky in October or even in November to try to hunt these guys down. They’re all magnitude 12.0 (visual) or brighter, and all three appear on chart 16 of Sky Atlas 2000, so you don’t need more sky atlas than that. But I suspect that you may find at least two of them quite a challenge to find, regardless of the size of your telescope.
NGC 6804 is the easiest to spot, at magnitude 12.0 and a diameter around 31 arc seconds. You’ll find it about 20 minutes of right ascension (about 4.5 degrees) nearly due west of Altair, the brightest star in Aquila. In my 13”, it’s small, not very bright, and featureless. The central star is listed at magnitude 14.4, and so it should be visible in larger scopes. But I did not note seeing the central star in my log entry dated July 1993 from Peach Mountain, nor did I record what difference any filters made. I guess I’ll have to try observing NGC 6804 a third time.
NGC 6803 is only about a degree almost due north of NGC 6804. It is a little brighter, at magnitude 11.4, but much smaller, only six arc seconds in diameter. Also, I did not know it at the time, but according to The Deep Sky Field Guide to Uranometria 2000, it has a “smooth disk with a brighter central region,” so it appears smaller visually. While scanning the area in my 13” at low power, I saw nothing that looked like a planetary nebula - just a lot of faint stars. So, I tried my OIII filter, passing it in and out between my eye and eyepiece. After carefully comparing the view with and without the filter, one of those little faint stars did not dim when the filter was present. Sure enough, there it was! Not much to see, though. I tried switching to higher power to see if I could see any detail, but even at about 300x, all it looked like was a slightly out of focus, greenish star.
John had challenged me with spotting NGCs 6804 and 6803, but I noticed NGC 6807 on the chart, about 3.5 degrees SSE of NGC 6804. So, I thought as long as I’m in the neighborhood, I’d check it out. Just as with NGC 6803, as I scanned the field at low power, I saw nothing that looked like a planetary. So again, I tried to “blink” it in using the OIII filter, which revealed its hiding place. Gotcha! Just like NGC 6803, NGC 6807 is tiny, star-like, and free of detail, even at high power. I found out later that it is magnitude 12.0, with an angular diameter of only two arc seconds. Now that’s small!
So, if you own a moderately large scope, and a narrowband light pollution reduction filter, and don’t mind getting off the beaten track, then you may wish to take a few minutes to hunt down these three planetaries. They’re not impressive visually, but they’re an accomplishment to find just the same. If you do manage to locate them, try putting higher power on them - I’d be interested in hearing what you see.