The Summer Triangle, a large triangle of bright stars (Deneb, Vega, and Altair), lies straight overhead on September evenings in the United States. Delphinus, Sagitta, and Vulpecula all lie in or near the Triangle. While none of these constellations are large, they all hold one or more interesting double stars or deep sky objects.
Delphinus, the Dolphin, is the easternmost of these three constellations. Delphinus is made up of a distinctive little parallelogram or diamond of four stars, with a fifth star a short distance to the southwest. Gamma Delphini, the star at the northeast corner of the diamond, is a well-known double star. The primary component star is yellow, but stargazers disagree on the color of the secondary. Some see it as white or pale blue, but most say it is pale green. I have personally never seen any shade of green in this star. Gamma Del is not a particularly wide double, but you should be able to split it without using high magnification.
Struve 2725, another double star, lies about 0.25° southwest of Gamma Del. Struve 2725 is somewhat tighter and fainter than Gamma Del, and is not an outstanding double by itself, but it pairs nicely with Gamma Del. Moderate to high magnification (~150×) will nicely split both doubles while keeping them both in the same field of view.
Sagitta, the Arrow, lies west of Delphinus and just north of the bright star Altair. Sagitta is similar to Delphinus in size and in the brightness of its stars. This little constellation really does look like an arrow pointing east-northeast.
An intriguing star cluster cataloged as M71 lies almost directly in the middle of Sagitta. M71 is classified as a globular cluster, but it is so loose that it looks a lot like a small rich open cluster. Moderate to high magnification will easily resolve the cluster.
Vulpecula lies just north of Sagitta, but since it consists of only two dim stars, its deep sky objects are easiest to find by starting from Sagitta. The brightest deep sky object in Vulpecula is an open star cluster known as the Coathanger. True to its name, the Coathanger bears a striking resemblance to a real coat hanger. This cluster spans about 1.5°, so it makes an ideal binocular target. The Coathanger is bright enough that a few of its stars are easily visible with the unaided eye under moderately dark skies. This cluster lies about 4° northwest of the pair of stars marking the southwest end of Sagitta.
Vulpecula also holds one of the finest planetary nebulas in the sky, the Dumbbell Nebula (M27). This nebula lies about 3° straight north of Gamma Sagittae, the brightest star in Sagitta. While most planetary nebulas are tiny, M27 is one of the few that are large, and it is the only planetary that is both large and bright.
M27 is easily visible in 10x binoculars as a fuzzy spot of light that is clearly bigger than a star. This nebula is easy to observe with good-quality small telescopes, but larger telescopes and higher magnifications continue to reveal more detail. The brightest part of the nebula is shaped like a dumbbell or apple core, with fainter nebulosity filling in the sides and making the nebula round. Although this nebula is bright enough to easily observe without a filter, an OIII filter will help bring out detail, especially in the nebula’s fainter areas.