Aquila, the Eagle, is a mid-sized constellation that lies right along the summer Milky Way just south of the zenith on September evenings in the mid-northern latitudes. Altair, the brightest star of Aquila, marks the southern corner of the Summer Triangle, an asterism (group of stars not classified as a constellation) that consists of the three brightest stars in the northern summer sky. On either side of Altair lie two somewhat dimmer stars, forming a distinctive line that’s vaguely reminiscent of Orion’s belt stars. The rest of Aquila consists of two outstretched “wings,” and a “tail” that points southwest down the Milky Way.
One of the more unique objects in Aquila is a dark nebula called Barnard’s E (cataloged as B142 and B143). Barnard’s E gets its name from its distinctive shape, which closely resembles the capital letter “E.” This nebula lies about 1.5° west of Tarazed, the star just to the northwest of Altair.
If you haven’t observed dark nebulas much before, it may take a bit to see Barnard’s E. Unlike bright nebulas, which emit or reflect light, dark nebulas are not illuminated; they just block out light from the stars beyond them. So, instead of looking for a visible cloud of gas, you’ll be looking for a mostly starless area in a field that’s otherwise rich with stars. Once you see the E, it should be fairly obvious. A relatively dark sky is critical to finding Barnard’s E; you’ll want to be able to see as many faint stars as possible to make the nebula stand out well. This nebula is large enough to be easily visible with binoculars. A telescope will also work for viewing Barnard’s E, but use very low magnification to allow you to see as much sky as possible around the nebula; this will make it more obvious.
Several planetary nebulas lie within the bounds of Aquila. One of the best of these is NGC 6781. This nebula lies almost exactly one-third of the way from Delta Aquilae (the star in the middle of Aquila) to Zeta Aquilae (the brighter of the two stars marking Aquila’s right wing). Planetary nebulas tend to be tiny; NGC 6781 is larger than most, although it’s small enough that you’ll want to use moderate to high magnification after you’ve located it. This nebula is almost circular, with a slightly brighter rim that extends most of the way around the nebula. You should be able to find NGC 6781 with a 6–8” telescope, but this nebula is faint enough that larger scopes will give much brighter and more detailed views of it. UHC or OIII filters will increase the contrast of this nebula.
Aquila also contains several open star clusters. Most of these are rather unimpressive, but NGC 6709 is one of the exceptions. This cluster is observable with binoculars as a faint fuzzy spot, perhaps with a couple of the brightest stars resolved. However, you will get your best view with a telescope at low to moderate magnification. NGC 6709 is not exceptionally rich, but it stands out nicely from the background starfield. Its stars are arranged in a roughly triangular shape. This cluster lies 5° southwest of Zeta Aql.
You can find M11, the Wild Duck Cluster, by starting from Aquila, even though it is techincally in Scutum. To find it from Aquila, first locate the star Lambda Aquilae, which marks the tail of the eagle. Two slightly dimmer stars curve westward from Lambda Aql, forming a short curved line. M11 is about 1.5° west of the western end of this line.