M16, the Eagle Nebula, is a beautiful and often photographed object in the southern sky (when viewed from the northern hemisphere). It is the northern-most of a series of well known objects in the area, including M17, M18, M20, and M8. But in this photo M16 is in the lower right corner and the object in the upper left is farther north. What’s interesting about this is that although the object in the upper left is quite bright (and although smaller than M16, not particularly small compared to typical astronomical targets), it has no common name. In fact, so far I have not even been able to find a catalog designation for it. Below is the annotated results from Astrometry.net, a service that identifies objects in astro-photos:
In addition to several different names for M16, two NGC objects, both star clusters, are identified. But the bright nebula is not. I suspect that it is included in some catalog, but it is clearly not a well know object.
Perhaps part of the reason is that M17 is about the same distance away from M16 in the opposite direction. Indeed, if you were to do an internet search for “M16 widefield image” the results would include many images showing M16 and M17, and some showing a large portion of the southern Milky Way, but very few if any images showing these two objects. It might also be true that the “mystery object” is very hard to spot visually. This is a hydrogen-alpha narrowband image, which shows light that is very difficult for humans to see through a telescope (visual observing). M16 has a lot of light in the blue-green range (oxygen-III and hydrogen-beta), which is more easily seen. Remember that the vast majority of common objects in space were discovered (and named) through visual observation, not photography.
I had just one clear night recently to capture this image and used it to get just the H-alpha data, so I don’t yet know whether there is any O-III in the area. I hope to capture the O-III and S-II data soon. In the mean time, if anyone can identify this object, please let me know.