Amateur astronomers often refer to Summer as Galaxy Season and for good reason since there are so many galaxy groups to observe during the summer. I tend to think of it as Cluster Season and Nebula Season too because looking toward the center of the Milky Way there are so many clusters to see in our galactic halo. The same is true of H-II (molecular hydrogen) star-forming regions and planetary nebulae. There is much to see and enjoy in the summer sky.
Of course, we city dwellers rarely see any of these wonders unless we leave home to visit less populated sites. The imperfect alternative to travel to a dark site is narrowband astrophotography. Last night, with a gibbous moon in the southeast, I pointed my astrograph to a pair of beautiful nebule in the constellation Sagittarius. The larger one in the image below is M8, the Lagoon Nebula. It’s a stellar nursery and home to NGC 6530, the cluster of young stars in its periphery.
The other nebula is M20, the Trifid Nebula, named for its tri-partite appearance. It too is an H-II region with a nascent open cluster forming within it. The Trifid also had a cloud of dust that in this image would lie to the left of the reddish nebula. In a natural light image, this dust would appear blue because it is not emitting light but simply reflecting light from nearby stars. I have such an image, taken several years ago, from Casitas de Gila in New Mexico. Alas, my narrowband filter attenuates the blue wavelengths, and the lovely reflection nebula does not appear in my image below.
This image is the composite of 8, 360-second frames taken through the 130mm astrograph fitted with a quadband filter.
Below, I have cropped the image to emphasize each object.
Both of the objects could benefit from another four to six hours of imaging time, but that isn’t going to happen soon simply because our forecast here is for a week or more of clouds and, if we are lucky, some rain.