Slowly we leave the summer behind and within a short while the autumn knocks on the door. The constellations, characteristic for the summer are moving a bit further West each night an we meet constellations we haven't seen this year.
We start September with some interesting objects in and around Cygnus. A special duo on the Cygnus-Cepheus border are the spiral galaxy NGC 6946 and the open cluster NGC 6939. The open cluster is pretty faint but rich. Through small telescopes there are about a dozen stars to resolve. The bigger you're telescope, the more stars you will see sparkle. Only 39' SE of NGC 6939 we'll find the galaxy NGC 6946. Because of it's low surface brightness this galaxy is difficult to see when the sky isn't totally dark. Through small telescopes there is not more to see than an obvious spot. The larger you're aperture, the more details you perceive. Through medium sized telescopes there is a diffuse, oval spot visible with a thickening in the core. Try to observe these objects with a low magnification, so you can get both objects in one field of view. The big contrast gives an extra dimension to these objects!
One of the weirdest objects I've seen is The Blinking Planetary (NGC 6826), because of it's obvious blinking effect. This planetary nebula is visible as a star with, through small telescopes and averted vision, a green/bleuish halo around it. As soon as you look straight to the planetary, the halo will disappear. It can be a bit difficult to find this object. Look for two stars of magnitude 8.5 and 10.5. The fainter of these two stars is the planetary's central star. When you look to the brightest star, you suddenly see the halo around the central star. But when you look at this star, the halo disappears again. Switching between these stars causes the planetary to 'blink'. This effect shows up to more planetary nebulae with a prominent central star.
The open cluster NGC 6819 is a beautiful object. There are a lot of faaint stars in this cluster that makes a large contrast with the glow of the Milky Way. Because of this contrast, and because of the specific shape of the cluster that looks like a 'W', it's easy to find and reconize the cluster.
Next we take a look at another challenging object in Cygnus: Campbell's Hydrodgen Star (PK 64+5.1). This is the star of a small planetary nebula that makes its halo glow. Search with a large telescope and low magnification to an orange star (the colour is less obvious at high magnifications). If you have found the star and you magnify the object, the nebula becomes visible. Unfortunately filters don't have any effect on this planetary.
We leave Cygnus to observe two beautiful open clusters in constellation Lacerta. We start with NGC 7209. This cluster is visible through large binoculars as a long, faint, spot. Three stars of magnitude 8 to 9 are easily visible within this glow. Telescopes resolve the loose cluster and show a lot of faint stars.
More north of NGC 7209 we find another significant open cluster: NGC 7243. This cluster looks just like its neighbour through large binoculars as a long spot with three stars of magnitude 8 and 9. Despite the irregular shape and the glow of the Milky Way, this cluster is pretty good visible.
We aim our telescopes to the constellation Andromeda where we find a bright blue planetary nebula: The Blue Snowball Nebula (NGC 7662). Through binoculars this nebula is hard to distinguish from a regular star, except for its prominent blue/greenish colour. Through small telescopes it's already obvious why this is called the Blue Snowball. There is an almost perfect round, blueish nebula visible. It's hard (but not impossible!) to see the central star, because of its great brightness of the planetary nebula.
A real challenge is the galaxy NGC 7640, two degrees SW of the Blue Snowball. It's pretty big and has a low surface brightness. This makes the object hard to see. Through medium sized telescopes this object looks like a really faint stroke with a slight brightening in the centre.
The double star Almach is already visible with the naked eye, because of it's magnitude of 2. But it's not possible to separate this double star yet. Also through binoculars this is not possible. The duo is separated 10 arc seconds and it's easy to separate the pair through telescopes. The main star is orange, the fainter companion blue. The companion itself is also a double star. This binary is separated at only 0.5 arc seconds. That makes this double hard to split, even through 10 inch telescopes.
In constellation Triangulum we find The Triangulum Pinwheel Galaxy (M33), the third largest galaxy of the Local Galaxy Group. At a distance of 'only' 2.4 million light years this is, after the Andromeda Galaxy, the closest galaxy to earth. Because M33 has a low surface brightness, it's a pretty faint object and hard to find in smaller telescopes. The reason for this is that a lot of beginning stargazers expect to see a small, bright galaxy instead of a large faint one. So they simply overlook the object. You can observe this galaxy best on moonless nights.
Finally we discuss two objects in Pegasus. We start with the galaxy NGC 7331. This object is best observed through medium sized or large telescopes. It will be visible as an oval, relatively bright, spiral galaxy. This object is especially impressive through large telescopes. On the eastside there are four compagnion galaxies: NGC 7335, -7336, -7337 and NGC 7340. These galaxies are visible through large telescopes with averted vision.
We finish this month with the barred spiral galaxy NGC 7479. This galaxy with its special shape is already visible through medium sized telescopes, but you need a large opening to see details in this object. The spiral arms are also visible through the large telescopes.
